The Principles Of Digestive Physiology Which Decree Correct Food Combining

The Basis Of The Food Combining System

The food combining system, as a whole, is simple and easy to understand. It logically evolved from

the study of gastric physiology and the actions of enzymes and digestive juices. Hygienic food selection and the principles or food combining are based on the nutritional needs of humans and the limitations of our digestive systems.

It is not what we eat, but what we digest and assimilate, that determines the nourishment our bodies receive. Food combining is based on the discovery that certain combinations of food may be digested with greater ease and efficiency than others.

Correct food combinations result in an immediate improvement in health by lightening the load of the digestive organs. Better nutrition is assured, and there is better digestion, less fermentation and putrefaction, more comfort, less distress and less gas.

So-called food allergies often disappear as a result of proper food combining. (See article in the Case History section of this lesson. This article was written by Richard Hill, a young man who had to learn the hard way.)

Fermentation causes irritation and poisoning. Proper food combining removes fermentation as a cause of indigestion (though there are many other conditions that can cause digestive problems, such as overeating; eating hurriedly or when tired, worried, angry, fearful, grieved, etc.; or when you are in pain or have a fever or inflammation).

The successful results obtained through the utilization of me food combining rules can be explained and substantiated by the facts of physiological chemistry, particularly the chemistry of digestion.

No food program, nor any food combining program, will cure disease. Healing can be effected only by removal of the causes of disease. Incorrect food combinations can be an important cause.

What Is Food ?

Food is any substance which is eventually convertible into such end-products as tissues, body fluids, etc., and can be utilized by the organism in the performance of its functions. To be correctly classified as a food, a substance must:

  1. Be capable of liberating energy when oxidized;
  2. Be capable of being utilized  for growth, maintenance and repair;
  3. Be capable of being stored within the body and
  4. Produce no nutritionally significant toxic effects

For example, some plants contain large amounts of oxalic acid (see definition) and should not be used as food. Many plants which contain smaller (nutritionally insignificant) amounts of oxalic acid are excellent foods. On the other hand, tobacco, which is a plant, contains proteins, carbohydrates, minerals, vitamins and water, which are the constituents of food. But tobacco also contains considerable quantities of poisons. Dr. Shelton says that one of these is one of the most virulent poisons known to science. Therefore, tobacco cannot be a food.

Nutrients in foods are chemical substances of known composition and structure, classified as carbohydrates (such as sugar, starch and glycogen); lipids (fats); proteins (amino acids linked together); salts (minerals); and vitamins, needed in small quantities (or, traces) by the body. In addition, foods contain indigestible materials—cellulose (fiber).

Water, oxygen and vitamins, together with proteins, carbohydrates, fats and minerals, form the constituents of the body—the blood, tissue, bones, organs, muscles and so forth. Foods must be taken into the digestive tract and prepared for use by the organism before their constituents may be used by the body.

The Best Food Is Raw Food

In our discussion of food combining, cooked foods and flesh foods will be mentioned. Uncooked foods from the plant kingdom constitute the ideal Hygienic diet, for those not yet ready to use exclusively raw plant foods, information on food combining of other foods is included.

People with impaired digestion may have been advised to avoid raw food. If serious pathological conditions exist, or if there are organic limitations caused by surgery, it would probably be advisable for such people to seek the help of a Hygienic doctor. Most such people can be helped by Natural Hygiene, but some of them may need careful supervision in changing from conventional eating and living patterns.

People whose digestive impairments limit the use of uncooked food should utilize raw foods to whatever extent they can while they aim for restoration of as much normal function as possible. The rational approach to such restoration of normal function is not drugs or surgery, but rest and fasting, followed by a gradual implementation of improved eating and living practices, adapted to the limitations of that individual.

The goal should be the gradual achievement of a diet predominating in uncooked foods, because the nutrients available in raw foods are several hundred percent greater than those remaining after food has been cooked or otherwise processed. More details about the damage done by cutting, cooking, seasoning and flavoring food will be given in future lessons.

Raw foods improve the total inner environment. Sluggish bowels begin to move, eventually cleaning out waste that may have been lodged in the folds of the intestine for months. The layer of mucus that forms in the intestines when cooked food predominates is removed, greatly increasing efficiency in the absorption of nutrients.

Food wastes don’t stay in the bowel long enough to putrefy. The transit time of raw food in a healthy body is 20 to 24 hours, while cooked food may take three days or longer.

Many scientific researchers arid medical doctors now, recognize the value of raw food, both in health maintenance and for improvement or remission in chronic illnesses.

John M. Douglass, M.D., internal medicine specialist at the Southern California Permanente Medical Group in Los Angeles says, “It’s a sad commentary that we think we can compensate with a pill for all the heat-labile nutrients and enzymes that are lost in cooking.”

He says also that experience shows that the raw food diet works for many diabetics, although it’s not always easy for them to follow and must be planned carefully.

Dr. Paul Kouchakoff, medical researcher of the Institute of Clinical Chemistry, Lausanne, Switzerland, revealed circa 1930 that after eating cooked food, the human body develops leucocytosis, the abnormal proliferation of white blood cells. Leucocytes are created and rushed to the intestine. When he fed patients on an 80 percent raw diet, no leucocytosis developed.

More details about Dr. Kouchakoff’s experiments, and other reports about the phenomenally superior value of raw food, will be given in future lessons. The above preliminary information is included in this lesson so the student may, at the outset, be motivated to apply his newly-acquired knowledge of food combining principles to the best food available, which, undeniably, is food that is utilized in its unchanged raw state.

The 80 percent raw food diet: For those who are not yet ready, or willing, to change to an all-raw diet, a good start would be the achievement of an 80 percent raw diet. For most people, this is not difficult to achieve. It can be appetizing, interesting, varied, satisfying and economical.

The information in the two lessons on food combining will contain all the details you need about utilizing both raw food and (if you use it) cooked food, so that you may work out your goal of eventually achieving an all-raw diet, even if you must take a roundabout route by first implementing the 80 percent raw diet.

The best and quickest way to achieve an 80 percent raw diet is to never eat cooked food more than once a day, and as part of only one meal. One should try for more and more days on raw food only. Even the people who are coping with digestive problems may eventually achieve these goals as they learn to apply the principles of Natural Hygiene to their own needs.

Food Classification

Foods vary widely in character and nutritional constituents. In order to intelligently implement the principles of food combining, reference points are necessary. A food classification chart will be included with Lesson No. 23, listing and classifying specific foods. In this current Lesson No. 22, we will classify the broad categories in which foods can be placed.

This classification of food categories will provide clarification and greater understanding of our discussion of the principles of digestive physiology and chemistry that decree correct food combining.

Proteins: All foods contain  some protein,  and the amounts of protein in different foods vary widely. We classify as protein foods those that contain a comparatively high percentage of protein—these are the concentrated protein foods. Such foods include:

  1. Nuts and edible seeds
  2. Soybeans
  3. Animal proteins
  4. Cheese
  5. Eggs
  6. All flesh foods (except fat)

The less concentrated proteins include avocados, olives, coconuts and milk. Combination foods (starchy proteins, to be combined as starch) include legumes, grains, peanuts and chestnuts: Green vegetable proteins (to be combined as starch) include peas in the pod, lima and other beans in the pod, and mature green beans in the pod. Sprouts contain significant amounts of protein, especially in the early stages. (More about sprouts later in this lesson and in Lesson No. 23)

Bananas (1.1 percent) contain almost as much protein as avocados (1.3-2.2 percent) and olives (1.4 percent). Dried fruits (2-5 percent) may contain twice as much protein as avocados. Broccoli (3.6 percent), brussels sprouts (4.9 percent), collards (4.8 percent), sweet corn (3.5 percent), kale (6 percent) and a number of other vegetables contain more protein than avocados.

Romaine lettuce (1.3 percent) contains valuable protein. None of these foods are classified in the protein category, but should, nevertheless, be regarded as excellent sources of protein.

Starches: The carbohydrates are the starches and sugars. The combination foods (starchy proteins) referred to under the protein category are classified as starches for purposes of food combining. These include dried and fresh legumes, grains, peanuts and chestnuts.

The starchy vegetables are potatoes, mature corn, parsnips and salsify, as well as Jerusalem artichokes; the mildly starchy vegetables are carrots, globe artichokes, beets, winter squash and several others (complete list in the classification charts in Lesson No. 23).

Nonstarchy and green vegetables: Lettuce, celery, cabbage, broccoli, summer squash, turnips, green beans, kale and a long list to be found in the classification charts.

Fats: The recommended fats are nuts, seed and avocados. No other fats are recommended. (See charts)

Fruits: Divided into three categories—sweet fruits, subacid fruits and acid fruits. Bananas, persimmons, sweet grapes and fresh figs, as well as all dried fruit, are in the sweet fruit category. Sweet apples, sweet peaches, pears, sweet cherries, some grapes and several other fruits are subacid fruit. Citrus, pineapples, strawberries and all tart fruits are in the acid fruit category. (See classification charts for complete listings.)

Tomatoes: Acid fruit without the sugar content of other acid fruits. Used with vegetable salad or any green nonstarchy vegetables, but not at a starch meal. May be used with nuts or seeds, as well as with avocados.

Melons: Watermelon, canteloupe, honeydew and many others. (See charts)

Syrups and sugars: All kinds of sugar, syrup and honey—not recommended.

The Chemistry And Physiology Of Digestion

For food to be utilized by the body, it must first undergo a series of processes which we call digestion. After we perform the only really voluntary actions involved in the process of nutrition—putting the food into our mouths, chewing and swallowing—the balance of the digestive process is the function of the autonomic or involuntary nervous system.

The changes which foods undergo are largely effected by enzyme and digestive juices. The conditions under which “such action” can occur are sharply defined, and this is the logical foundation of the food combining system. Physiologists have ascertained the details of the chemistry of digestion through long and painstaking labors. It has remained for the Natural Hygienists to make practical application of this great fund of vital knowledge.

Knowledge of the physiology and chemistry of digestion can lead us all to a food program that will insure better digestion and better nutrition.


Enzymes are proteinaceous organic catalysts in all living organisms, both plant and animal. Our digestive juices contain enzymes that accelerate chemical reaction by catalytic action, without themselves being used up in the process.

Digestive enzymes can be used over and over again but eventually are replaced by the body. There are many different kinds of enzymes, and digestive enzymes are not the same as the enzymes in raw, unprocessed food. Digestive enzymes break down the complex substances we ingest into simple components that can be utilized by the body.

There are five types of digestive enzymes in the human body.

  1. Hydrolases facilitate hydrolysis, the breakdown of substances in water within the body.
  2. Adding enzymes build proteins by adding amino acids, one by one.
  3. Transferring enzymes transfer organic substances from one compound to another so the body may use them in various ways.
  4. Isomerases, or rearranging enzymes, rearrange molecules  in  organic  substances;  they  also  rearrange amino acid enzymes.
  5. Oxidases, or oxidizing enzymes, are released in the presence of oxygen and rapidly bring about a change in the color of food. They act on foods in the mouth while one is masticating or whenever the food is exposed to oxygen. These enzymes are also present in apples and other fruits. They are released when the fruit is cut and react so as to rapidly bring about, a change of color to brown.

It is not necessary to memorize the names of these enzymes, but the information about the, action of the different types of digestive enzymes will help you to understand the underlying rationale of food combining.

Each digestive enzyme is specific in its action. It acts only upon one class of food substance. Each stage in the digestion of food requires the action of a different enzyme, and the various enzymes can perform their work efficiently only if the preceding work has been properly performed.

Body chemistry is, to a large extent, determined by the the food we eat. When certain foods are eaten regularly, the digestive enzymes and secretions are of a character to handle those foods. When the diet is altered, more and more of the digestive juices secreted will be of a character to digest the foods in the new diet, and less and less of the digestive juices will be of the character to digest the foods in the old diet.

The type of digestive juice fitted for the digestion of one type of food is of no value in digesting another type of food. Therefore, it is essential that food be taken in combinations that do not interfere with enzymatic action.

The Process of Digestion

Digestive speed and efficiency vary with individuals and circumstances. However, certain general statements can be made. Fruits pass through the stomach quickly; low-protein and low-starch vegetables also pass through the stomach rapidly, with little change; vegetables containing much starch must be retained in the stomach longer, for more thorough digestion; and proteins require a still longer time »for gastric digestion.

Fruits may remain in the stomach for thirty to sixty minutes, low-protein and low-starch vegetables a little longer, concentrated starches about two hours and concentrated proteins approximately four hours. Some foods may take five or six hours or more to leave the stomach. Some examples are combination starch/protein foods like legumes (including beans), grains, cooked cabbage and flesh foods.

Most digestion occurs in the stomach and small intestine. Digestion, especially starch digestion, actually begins in the mouth, with mastication and insalivation of the food. This sends the proper signals for the release of the digestive juices suited to the character of the food eaten. Digestive juices are present in the saliva and in the gastric secretions of about five million microscopic glands in the walls of the stomach.

The digestive glands supply different enzymes and juices of varied strength and character and with specific timing, depending on the different foods ingested. The digestive juices may be more or less liquid, of varying degrees of acidity or alkalinity and with complex and elaborately contrived variations.

After food is masticated, insalivated and swallowed, gastric digestion is initiated. Involuntary movements of the stomach slowly mix the food with gastric juices secreted by the glands in the walls of the stomach. Pepsin, a protein-splitting enzyme, and hydrochloric acid are separated, as
well as lipase, a fat-splitting enzyme, mucus and diluting juice, along with other factors needed in the digestive process.

An alkaline secretion protects the walls of the stomach from the acids. Mucus is a natural lubricant that is secreted by the cells of the mucous membranes lining all of the hollow organs of the body. It keeps the body tissues moist and prevents them from drying and cracking.

A brief review of the process of digestion will help in understanding the food combining rationale. Gastric secretion is continuous (except during fevers, gastric inflammation, pain or strong emotions; fasting is indicated when any of these conditions are present). Of course, gastric secretion is unnecessary when no food is taken.

Hunger and the sight, smell, taste or thought of food stimulate gastric secretion. Usually about three pints of gastric juice is secreted every twenty-four hours and about half this amount is required to digest a hearty meal. If you eat more than two hearty meals daily, your account will be overdrawn.

As the process of digestion continues in the stomach and the food is mixed with the digestive juices, water (from the body’s reserve supply) is added to the mixture in a process called hydrolysis. During hydrolysis, digestive enzymes separate carbohydrates into simple sugars, and proteins into their constituent amino acids.

Since digestion is a mechanical as well as a chemical process, some cellulose is an important part of the diet. Although cellulose cannot be digested by humans (no enzyme secreted by humans is capable of splitting cellulose), it serves as bulk in the propulsion of food through the digestive tract. Cellulose also provides the bulk needed in the efficient elimination of food residues.

Juices and refined foods contain little cellulose. However, too large a quantity of cellulose is also undesirable. Therefore, we should use fresh fruits and, when using vegetables, strive to obtain the young, tender vegetables, as these contain smaller amounts of cellulose.

Food residues, fibrous materials and particles not thoroughly masticated proceed on to the colon. Peristalsis (wave-like muscular contractions) propels the food mixture back and forth in the stomach. Periodically, the most liquid portion of the mixture is discharged into the duodenum where it meets a very acid fluid. The resultant semi-liquid mixture, known as chyme, then proceeds further—into the small intestine—where it meets a very alkaline mixture of pancreatic juice, additional digestive enzymes and bile. (Bile is secreted by the liver and stored in the gallbladder to be used when needed, particularly for emulsifying fats).

The intestinal glands secrete a juice containing enzymes similar to pancreatic enzymes. Virtually all absorption should occur by the time the food passes through the small intestine, and the residue proceeds into the large intestine (the colon).

Through all these processes, the peristaltic contractions continue, longitudinally and circularly, and propel the chyme along the alimentary canal. As you can see, foods are not digested when they have passed out of the stomach. A large part of the work of digestion takes place in the small intestine. But the role of gastric digestion is an important one in preparing the food for the next stage in the digestive process.

Coffee, tea and other such toxic infusions cause a premature emptying of the stomach and thus cause foods to leave the stomach before gastric digestion is complete.

Digestion is governed by physiological chemistry, and this must be considered in the planning of meals that are compatible with the physiological limitations of the digestive glands and their secretions. This lesson will help in understanding the principle that the digestion of different foods requires digestive juices of different characters.

The study of the processes of digestion reveals the specific action of the digestive enzymes, the careful timing of their secretion and the adjustment of the strength and character of the digestive secretions to the character of the food upon which they are to act. Carbohydrate foods receive a juice rich in carbohydrate-splitting enzymes, protein foods receive protein-splitting enzymes, and so forth.

Starch Digestion

Starch digestion begins in the mouth with the action of the enzyme ptyalin (alpha amylase) which converts (or else begins the process of converting) starches into sugar during mastication and insalivation. The salivary secretions accompany the food to the stomach and salivary digestion of starches continues in the stomach for a long time, if the food was eaten under correct conditions.

If ptyalin is the only agent in the body capable of initiating starch digestion (and this is not certain), or whether it is simply the body’s first opportunity to initiate starch digestion, we must not disregard its importance. The chewing process in the mouth should mix food with saliva, but people have the tendency to swallow the mass too quickly to permit the enzyme to complete its action. This necessitates the continuation of the salivary action in the stomach.

It is important that starches be eaten dry, not moist. So, you should eat steamed or baked potatoes dry rather than in potato soup. The eating of liquids with starches promotes the tendency to swallow moist starch without thorough mastication, insalivation and emulsification, processes that are particularly needed for the digestion of starches. Drinking liquids or eating liquidy foods softens the food artificially and may also cause you to eat more food than if you had eaten it dry. Drinking at meals dilutes the digestive juices and also prevents thorough mastication and insalivation of the food.

If the ptyalin is destroyed or its action is inhibited and the digestion of starch is interrupted, the partially digested (and probably somewhat fermented) starch proceeds to the duodenum, where further starch-splitting enzymes are secreted. Starch that escapes digestion in the stomach may later be acted upon by pancreatic and intestinal enzymes, provided too much fermentation has not already occurred. It is also very possible that the interrupted gastric digestion may never be completed.

Ptyalin requires either an alkaline or neutral medium. Ptyalin is destroyed by even a mild acid. If fruit acids—or any acids—are taken with carbohydrates, especially with such as potatoes, beans, bananas or dates, digestion will be inhibited or prevented and fermentation may occur. Oxalic acid diluted to one part in 10,000 completely arrests the action of ptyalin. Significant amounts of oxalic acid are contained in rhubarb, spinach, Swiss chard, beet greens and purslane.

The acetic acid in a teaspoonful of vinegar can suspend salivary digestion. Tannic acid (in coffee and tea) inhibits starch digestion, as do drug acids. The combination of citric, malic and oxalic acids in tomatoes (which are released and intensified by cooking) interferes drastically with starch digestion.

People take oranges and grapefruit as part of a meal that includes cereal and/or bread, later complain that they feel great distress after such a meal and conclude that they cannot eat citrus fruit. Such a conclusion is based on their experience of a wrong combination—not of a wrong food. Fermentation frequently does occur as a result of eating acids with carbohydrates. All students of food combining know that this combination produces bad effects such as gas, sour stomach (hyperacidity) and contributes to great difficulty in digesting starches.

When foods are eaten in such incompatible mixtures, and the efficiency of digestive enzymes is inhibited, it is subjected to decomposition in the digestive tract. If the digestive enzymes cannot perform their intended functions of breaking down and hydrolyzing the food (adding water from the body’s reserve supply), bacterial decomposition may occur, resulting in fermentation and the production of alcohol and acetic acid.

Sugar, particularly, will readily ferment into alcohol, especially when combined with acids or protein. Natural combinations of citric acid or malic acid or other natural fruit acids combined in the whole fruit with fructose (also called levulose or fruit sugar) do not cause fermentation unless eaten with starches.

Alcohol, acetic acids and putrefying substances are byproducts of decomposition.

Putrefaction may be defined as the decomposition (as opposed to digestion) of protein matter by micro-organisms, producing malodorous and toxic substances.

Fermentation is the decomposition of sugar and starch, and their conversion by microorganisms into carbon dioxide, alcohol and acetic acids. Dr. Shelton says that digestion reduces food to the diffusible state without depriving it of its organic qualities, while fermentation renders food diffusible by reducing it to an inorganic and useless state. Digestion puts food in a solution, but fermentation disintegrates it.

A simple way to avoid production of these poisonous substances in the digestive tract is to learn, and implement, the Hygienic rules for food combining. They are perhaps of even greater importance than food selection. Persistent adherence to food combining principles has been known to reduce, or even eliminate, many digestive, nasal, skin and other problems, even in some people who have not changed to the Hygienic diet. It is obvious that elimination of incompatible food combinations is a giant step in the right direction.

Efficient digestion and good health can be possible only when we eat in such a way as to offer the least hindrance to the work of digestion.

Protein Digestion

The digestion of carbohydrates is so different from that of protein that, when they are mixed in the stomach, they interfere with the digestion of each other. Protein digestion starts in the stomach and acid enzymes are secreted when protein is eaten. Proteins require an acid medium for digestion so, upon ingestion, hydrochloric acid is secreted in order to activate pepsinogen; this immediately stops the digestion of starches.

Almost all foods contain some protein but, when we speak of protein foods in our study of food combining, we are referring to concentrated proteins like nuts and seeds, cheese, flesh foods, etc. (See Classification of Foods in Lesson No. 23 for help in identifying concentrated protein foods, concentrated carbohydrate foods, etc.)

The normal digestion, absorption and metabolism of protein requires thorough mastication of food, in order to break it down for propulsion through the digestive tract, and for action by the digestive enzymes. As previously indicated, hydrochloric acid and pepsin (and other acid gastric juices) are secreted for the initial phases of protein digestion in the stomach, and other enzymes, such as trypsin, continue the digestion in the small intestine in a slightly alkaline medium. Protein-digesting enzymes are also secreted by the pancreas.

Before the body can use proteins, they must be reduced to their constituent amino acids (the building blocks of protein). The body must break down the complex proteins in foods and synthesize its own protein out of the amino acids. Food combining rules are of major importance in the consumption of protein, since the complexity of this food element would seem to suggest that it be eaten only under ideal conditions.

Free hydrochloric acid to the extent of only 0.003 percent is sufficient to suspend the starch-splitting action of ptyalin. Only a slight further increase in acidity not only stops the action, but destroys the enzyme. All physiologists agree that even a mild acid destroys ptyalin. It has never been shown that saliva is capable of digesting starch without the presence of ptyalin.

The function of the gastric protein-splitting enzymes, such as pepsin, are prevented by an alkali. The physiologist Stiles says, “The acid which is highly favorable to gastric digestion is quite prohibitive to salivary digestion. The power to digest proteins is manifested only with an acid reaction and is permanently lost when the mixture is made distinctly alkaline. The conditions which permit peptic digestion to take place are, therefore, precisely those which exclude the action of saliva.”

The presence of undigested starch in the stomach interferes with the digestion of protein. Physiologists have shown that undigested starch absorbs pepsin, which is necessary for the digestion of protein.

Dr. Richard C. Cabot of Harvard wrote: “When we eat carbohydrates, the stomach secretes an appropriate juice, a gastric juice of different composition from that which it secretes if it finds proteins coming down.”

Combination Foods

Single articles of food that contain starch-protein combinations (grains, legumes, and a few others) are less difficult for the body to handle than when two foods are eaten with opposite digestive needs. The body is able to adjust its juices, both as to strength and timing, to the digestive requirements of combination foods.

The first response by the body is the releasing of an almost-neutral juice for digestion of the starch. After gastric digestion of starch is completed (about two hours), hydrochloric acid is secreted for digestion of the protein. The two processes do not go on simultaneously—rather, the secretions are minutely adjusted, in both character and timing, to the varying needs of the body to digest the complex food substance.

Such complex food substances are not ideal foods. They are usually cooked, and the fact that they require such complicated adjustments puts an additional strain on the body. Simple uncooked foods are easier for the body to process and offer the least hindrance to the work of digestion.

Beans: “Because of their complex character, beans, a protein-starch combination, tax the digestive powers more than simpler foods, but the gas, discomfort and other trouble that so commonly follow, eating them is not due so much to the beans themselves as to the company they keep.

Baked beans are preferable to beans that are boiled and taken saturated with water. If taken thus relatively dry, well chewed and eaten in proper combinations, beans are readily digestible.” This article about beans, which was published by Dr. Shelton in 1971, is evidently a somewhat revised opinion. In his Volume II of The Hygienic System, published in 1935, he suggested that beans should not be used.

I personally was formerly unable to tolerate lentils or beans of any kind, even when sprouted. I eliminated all legumes from my diet for about six months, after which I carefully experimented with small amounts, properly combined, until I seemed to build up my ability to digest them. Today I can eat sizeable servings of cooked or sprouted legumes (which I seldom do) and I have no problem with them.

Foods with Different Digestive Requirements

When two foods are eaten that have different or even opposite, digestive needs, the precise adjustment of digestive juices to meet requirements becomes impossible. Eating proteins with carbohydrates (sugar or starch) produces the same abortive situation as combining acids with carbohydrates, since protein digestion requires the secretion of acid enzymes and juices. All acids, including those in food and the acid protein-digesting juices, destroy ptyalin, the starch-digesting enzyme.

Arther Cason, M.D., D.P.H., F.R.S.A. (London), writing in the April, 1945 issue of Physical Culture, mentions two groups of experiments made by him and his aides which showed that eating protein and carbohydrate at the same meal retards and even prevents digestion. He made control tests in which digestive rates were recorded, and a final analysis of the feces was made.

He says, “Such tests always reveal that the digestion of proteins when mixed with starches is retarded in the stomach; the degree varying in different individuals, and also in the particular protein or starch ingested. An examination of the fecal matter reveals both undigested starch granules and protein shreds and fibers, whereas, when ingested separately, each goes to a conclusion.”

As indicated by Dr. Cason, there is an individual variation in the response to certain food combinations. This would seem to account for the fact that certain people exhibit overt symptoms from the use of certain food combinations, while others do not. However, the mere fact that overt symptoms are not observed is not proof, per se, that the food is being properly utilized.

Potatoes are said to be the least objectionable of any starch to be used with protein. Dr. Shelton is of the opinion that it is the rapidity with which potato starch digests that makes its combination with protein less objectionable than the combination of other starches with protein. Potato starch digests in ten minutes under ideal conditions and it would seem that the potato starch digests before the gastric juice can accumulate in quantity sufficient to interfere.

Even so, Hygienists have rarely been observed to use potatoes with nuts—either potatoes or nuts are so satisfactory as, an accompaniment to a salad that most of us would ask, “Why would we need both ?”

Food Combining Rules

Acid-Starch Combinations and Protein-Carbohydrate Combinations

The preceding discussion leads up to the presentation of the first two food combining rules, which I consider to be by far the most important of all these rules and the ones which should be thoroughly understood and implemented at all possible times.

  • Never eat carbohydrate foods and acid foods at the same meal.
  • Never eat a concentrated protein and a concentrated carbohydrate at the same meal.

The purpose of this lesson is to help you to understand the reasons for these rules; Lesson No. 23 will help you to learn to implement them.


Protein-Protein Combinations

  • Never consume two concentrated proteins at the same meal.

Two concentrated proteins of different character and composition (such as nuts and cheese) should not be combined. Gastric acidity, type, strength and timing of secretions for various proteins are not uniform. Since concentrated protein is more difficult to digest than other food elements, incompatible combinations of two different concentrated proteins should be avoided. Some people with impaired digestions find it necessary to limit themselves to only one variety of nuts/and or seeds at a sitting, but other people may find, upon experimentation, that two or three varieties of nuts or seeds may be used at the same meal, if desired.

Protein-Fat Combinations

  • Do not consume fats with proteins.

Our need for concentrated fat is small and moil protein foods already contain a good deal of fat. Most nuts contain about 10 percent to 20 percent protein, and about 45 percent to 70 percent fat. Avocados contain about 1.3 percent protein (Florida varieties) to about 2.2 percent or a little more (California varieties) and 11 percent to 17 percent fat. Most other protein foods are high in fat, including cheese, eggs and flesh foods. The only protein foods not high in lat are legumes, skim milk cheese and lean meat.

Fat has an inhibiting influence on digestive secretion and lessen the amount and activity of pepsin and hydrochloric acid, necessary for the digestion of protein. The fat may lower the entire digestive tone more than 50 percent. Since most proteins already contain a good deal of fat, it would certainly be contraindicated to add more to the meal.

Fats in Combination with Other Foods

  • Use fats sparingly.

Fats also delay the digestion of other foods and, if used with starch, it will delay the passage of the starch from the stomach into the intestine. Fat not only inhibits the secretion of gastric juice—it also inhibits the physical actions of the stomach. Too much fat taken with a meal results in acid eructations and a burning sensation in the throat.

When fats (avocados or nuts) are eaten with green vegetables, preferably raw, the inhibiting effect of fats on gastric secretion is counteracted and digestion proceeds quite normally. The use of fat (avocados) with starch is considered acceptable, provided a green salad is included in the meal.

Avocados: Though not a high-protein food, avocados contain more protein than milk. They are high in fat and the small percentage of protein they do contain is of high biological value. They are best used with a salad meal. Since they are so high in fat that they tend to slow down the digestion of foods normally requiring a shorter digestion time, they are perhaps only a fair combination with subacid and acid fruit.

They are usually considered a poor combination with sweet fruit, especially dried sweet fruit. However, let us consider some recent work on this subject.

In an article on this topic, Dr. Vetrano says that exceptions may sometimes be made in combining avocados with fresh sweet fruit, such as bananas, but that avocados should not be combined with dried sweet fruit, unless it has been soaked overnight. She also says, “Eating avocados with salad enhances their digestion. The next best combination for the avocado is taking it with subacid or acid fruit.

The fat in the food does not seem to interfere with the emptying time of the stomach and we have excellent results with this combination. The protein, which is about 2.1 to 2.5 percent, is not sufficient to interfere with the digestion of fruit. It is even better when lettuce leaves and celery are eaten with the fruit and avocado. By diluting the fats and the sugars with the lettuce, the emptying time of the stomach is not depressed.

Those who have weak stomachs with poor muscle tone would probably do better by taking avocado only with vegetable salads. If lettuce is taken with a sweet fresh fruit and avocado, even these digest well. It is probably best to never combine avocado with sweet dried fruit unless it is just a small amount of both eaten with a great deal of vegetables.”

Since the avocado is low in protein, it may also be used with potatoes or other starch foods. Some
people like to use avocado with the potato instead of using butter. However, I must reiterate, the best way to use avocado is with the salad.

Avocados should never be used with nuts, which are also high in fat, nor should they be used with melons.

The only fats we have considered here are nuts (a protein/fat food) and avocados (a low-protein/fat food). Other fats will be listed in the food classification chart in Lesson 23, but they are not recommended for regular use. Most of them should never be used.

Acid-Protein Combinations

  • Do not eat acid fruits with proteins.

Citrus, (tomatoes: see discussion), pineapple, strawberries and other acid fruits should not be eaten with nuts, cheese, eggs or meat. Acid fruits inhibit the flow of gastric juice. The digestion of protein requires an unhampered flow.

This is one rule that has given rise to some disagreement and controversy. Although Dr. Shelton includes in this rule the prohibition of citrus and tomatoes with nuts and cheese, he goes on to say that nuts and fresh cheese do not decompose when used with acids, but have their digestion delayed. He also says that acids do not inhibit the flow of gastric juice any more than does the oil of nuts or the cream of cheese.

Many Hygienists use tomatoes with nuts and believe they cause no problem. Citrus fruits present a different situation, due to the sugar in the fruit, which can ferment if its digestion is delayed by the nuts. Various experiments with the use of citrus fruits combined with nuts have produced differing results. Some Hygienists continue to use citrus with nuts.

If sweet oranges are used at the same meal with nuts, the precaution of waiting thirty to sixty minutes after eating the citrus is sometimes observed. Grapefruit might be better suited to combining with nuts, since it usually has a much lower sugar content.

Citrus fruit is best used alone but may be combined with other acid fruits; nuts are best used with salad.

Dr. Shelton modified this rule somewhat on Page 52 of Food Combining Made Easy: “Although green vegetables form the ideal combination with nuts, acid fruits form a fair combination with these foods and may be taken with them.”

Dr. Percy Howe, of Harvard, says: “Many people who cannot eat oranges at a meal derive great benefit from eating them fifteen to thirty minutes before the meal.”

Dr. Vetrano is convinced from her experience at the Health School that nuts should not be used with citrus fruit and she discontinued this practice some years ago.

A corollary of this same subject is the use of some subacid fruits with nuts or cheese-primarily tart or semi-sweet apples, although some other fruits which are usually considered subacid are sometimes used in this way. The same principles would apply as with the use of oranges with nuts, provided the sweeter subacid fruits, such as Delicious apples, are not used.

Such acid-protein combinations as sour salad dressings and acid fruit drinks used at conventional meals serve as a check to hydrochloric secretion.

Sugar with Starch, Protein and Acid Fruit

  • Do not combine sweet fruits with foods that require a long digestive time-foods such as proteins, starches and acid fruits.

The sugars in sweet fruit should be tree to leave the stomach quickly, in perhaps fifteen or twenty minutes, and are apt to ferment if digestion is delayed by mixture with other foods.

Sugar-starch combinations cause additional problems.

When sugar is taken, the mouth quickly fills with saliva, but no ptyalin is present. Ptyalin is essential for starch digestion. If starch is disguised by sugar, honey, molasses, syrup or sweet fruit, the signals are scrambled and digestion is impaired.

Monosaccharides and disaccharides ferment more quickly than polysaccharides. (See definitions) No digestion of sugars takes place in the mouth or stomach; fermentation is inevitable if sugars of any kind are delayed in the stomach awaiting the digestion of starch, protein or acid fruit.

Sugar also has a marked inhibiting effect on the flow of gastric juice and on gastric motility. No other food depresses the action of the stomach and the desire for food as does sugar.

Starch-Starch Combinations

  • Eat but one concentrated starch at a meal.

This rule is probably more important as a means of avoiding the overeating of starches than as a means of avoiding bad combinations. But it is true that starch foods may differ greatly. If two different starches are eaten together in small quantities, this is thought to not cause problems.

Slightly starchy vegetables may be combined with more starchy vegetables (e.g. carrots with potatoes), but not with combination foods (starch/protein foods) such as grains and legumes.

Acid Fruits, Subacid Fruits, Sweet Fruits

  • Acid fruits may be used with subacid fruits.

This is an acceptable combination, though some subacid fruits are rather high in sugar and the acid fruit may delay the sugar’s normally quick exit from the stomach. However, there is no sharp line of division between the acid and subacid fruits. If combining subacid fruit with acid fruit, it is better to use only the less subacid fruit.

The acid fruits are those with the tart flavors, for example, citrus, pineapple, strawberries, and certain varieties of apples and other fruits. Tomatoes are also considered acid fruit (without the sugar content of other acid fruit). Tomatoes should not be combined with subacid fruit, nor any other kinds of fruit.

They are best combined with the salad at a meal at which no starchy foods are served. Do not use acid fruits with sweet fruits, as previously indicated.

Acid fruits are best used alone (a single variety), but if used in combination with other acid fruits, this is considered an acceptable combination.

  • Subacid fruits may be used with sweet fruits.

There is no sharp line of division between subacid fruits and sweet fruits. When using subacid fruits with sweet fruits, it is best to use the sweeter varieties of subacid fruit. The subacid fruits are those that possess a slightly acid flavor (but not tart), such as pears, certain apples, grapes, etc. Grapes, for example, can be acid, subacid or sweet. The sweet fruits are those that are rich in sugar and taste sweet-bananas, persimmons, sweet grapes, and so forth, and all dried fruit.

Some people prefer to eat bananas alone, but most people have no difficulty in combining them with subacid and other sweet fruit at a fruit meal. Dr. Shelton says, “While I have found that bananas combine fairly well with dates, raisins, grapes and a few other sweet fruits and with green leafy vegetables, such as lettuce and celery, I have noted that they digest best if eaten alone. This calls, to mind the fact that Tilden, also, after much testing of the matter, reached the conclusion that bananas are best eaten alone.”

Dried sweet fruits should be used sparingly. Use but one kind at a meal, in small amounts, combined only with subacid fruit and/or fresh sweet fruit and/or with lettuce and/or celery. Overeating of dried fruits .will often bring on symptoms similar to a “cold”.

The sugar concentration is naturally greater in fruits which have been dried. Some dried fruits, esp. dried apricots, should be soaked overnight to replenish the missing water. Dates are usually used without soaking, figs or raisins can be used either way. If they are rather hard, soaking will soften and improve them.

Dr. Vetrano recommends using as little soaking water as possible, soaking one side at a time, so all water will be absorbed, thus avoiding loosing flavor and nutrients. It is important that the water used for soaking be distilled water.

Sweet fruits combine fairly well with subacid fruits, provided the subacid fruits are on the “sweet side,” for example, use Delicious apples, not Macintosh or Jonathans, with sweet fruit.

It is best to have these fruits at a fruit meal combining only with lettuce and/or celery. Since fruits are usually high in acids or sugars, they do not combine well with other foods.

Fruits with Vegetables

  • Do not combine fruit with any vegetables except lettuce and celery.

It is best not to combine fruits with vegetables (especially cooked vegetables), proteins or starches because if such a combination of food is eaten, the digestion of the fruit will be delayed and subject to fermentation. Lettuce and celery, however, may be combined with any fruit except melon, and will cause no problem.

Dr. Vetrano says, “Taking green uncooked vegetables with a fruit meal is perfectly all right. Even though some charts state that subacid and sweet fruits combine fair to poorly with green uncooked vegetables, the feeding practices at the Health School indicate that these are good combinations, indeed, even enhancing digestion of the fruit in some conditions of impaired digestion.”


  • Salads combine very well with proteins or starches.

Any nonstarchy vegetables may be combined with proteins or starch, except tomatoes, which should especially not be used with starches. The green leafy vegetables combine very well with most other foods. They are excellent food and should be used in the diet.

Lettuce and other green and nonstarchy vegetables leave the stomach with little change—they pass through the stomach rapidly unless delayed by oily dressings or foods that require a more thorough gastric digestion. Lettuce and celery are good combination with fruit because all of these foods require little gastric digestion.

However, even if these vegetables are held up in the stomach with other foods, as when using salad with nuts, there is no fermentation.

Eating a large salad of fresh raw vegetables (three or four varieties) daily is an excellent practice. Dr. Shelton says, “A large bowl of salad each day is required by everyone.”

Take Melons Alone

  • Do not consume melons with any other foods.

This rule has been somewhat under question in recent years. I personally have found that eating melons alone is an excellent practice, and have even found it advisable not to mix two different varieties of melon at the same meal.

Many people who have complained that melons did not agree with them have no trouble handling them when eating only melon at a meal. Yet, certain Hygienic professionals are offering some post-fasting people more than one variety of melon at a meal (even melons in combination with grapes or other subacid fruit) and some Hygienists follow this practice. If you want to experiment with these combinations, do it sparingly and carefully. But if you have a history of digestive problems, don’t do it at all.

Melons are more than 90 percent liquid and leave the stomach quickly if not delayed and fermented by combining with other foods. Dr. Vetrano says, “Melons are best taken alone because the sugar and other nutriments are in a less stable form than the nutrients of other fruits.

Orange juice may be kept in the refrigerator for an hour with little change in flavor, but if you refrigerate watermelon juice for only ten minutes, its flavor, color and composition markedly change. It decomposes much more quickly than other fruits. Consequently, if it is held in the stomach awaiting the digestion of other foods, it will decompose (ferment) and cause a great deal of gastric distress. Eating watermelon with nuts can really be troublesome.”

Dr. Shelton says, “Because of the ease with which melons decompose, they do not combine with any food, except, perhaps, with certain fruits. We always feed them alone, not between meals, but at meal time.”

He also says, “It is probably a great misfortune that we do not always feel the direct effects of imprudent eating immediately following a meal. For example, there are large numbers of people who have discomfort, even great discomfort following a meal in which melons are eaten with other foods, but there are many others who do not. This latter group can see no connection between their life of imprudent eating and the breakdown of their health in later years. Their apparent impunity prompts them to defy all the same rules of life.”


  • Alfalfa sprouts may be combined as a green vegetable.

Other sprouts should properly be classified in the same category as the original seed, even though the sprouting process has somewhat lowered the protein and carbohydrate content.

During the sprouting process, the carbohydrate and protein components of the sprouting seed tend to diminish, and the composition becomes more like a green vegetable instead of a legume, grain or seed. However, this is not uniformly the case. Sprouts which progress to the green leaf stage, such as alfalfa and mung beans, are high in chlorophyll, and alfalfa sprouts, particularly, may be freely combined as a green vegetable. Mung bean sprouts still retain enough of the property of legumes so that they are best eaten without other proteins or starches. These sprouts may be included in the low protein/starch category.

Lentils, soybeans, garbanzos and other miscellaneous beans and grains should be allowed to sprout only very briefly, until just a small sprout is showing—no longer than the seed, at most.

The change in character is therefore much less than for those sprouts which are sprouted to the green leaf stage. Sprouts are high in protein in these early stages. They should therefore be classified, with some expectations, according to their original food categories, namely, as protein or combination protein/starch foods.

Sprouted sunflower seeds may, of course, continue to be classified as protein. In the case of lentil, soybean and garbanzo sprouts, they could be classified as low protein, since the starch tends to diminish and the protein remains in significant amounts in the early stages of sprouting.

I would classify sprouted grains as combination foods, their original category, to be combined as starch.

My experimentation with these sprouts, and my research on the subject, leads me to these conclusions as the best way to classify and combine them. More detailed information about sprouts and sprouting will be given in a future lesson.


Milk, Yogurt and Clabber

  • Milk is best taken alone.

This rule is included because it is one of Dr. Shelton’s food combining rules, and because this lesson on food combining may be helpful to those still on a mixed diet. Hygienists do not drink milk. Adults do not need any kind of milk. Infants need their mother’s milk; if this is not available, they need a substitute. (More about this in a future lesson.)

Dr. Shelton says that the use of acid fruits with milk does not cause any trouble and apparently does not conflict with its digestion. This would also apply to clabber (sour milk) or yogurt, which may be preferable to milk for adults.

Many adults (and some children) lack the enzymes lactase and rennin necessary for the digestion of milk. Lactase catalyzes the conversion of lactose (milk sugar) to the glucose and galactose which can be utilized by the body. Rennin is a milk-coagulating enzyme, which many adults no longer secrete.

This is also the reason that cheese is considered preferable to milk, although no dairy products are recommended for regular use.

The thymus gland, which also has a function involved in the digestion of dairy products, reaches its maximum development during early childhood, and usually degenerates and becomes vestigial in adults.

None of these products are recommended. If any milk products are used, they should be raw (unpasteurized) and should not be used on a regular basis. Yogurt cultures, particularly, can inhibit the body’s own natural production of beneficial intestinal flora.

Dr. Shelton says that either sweet milk or sour milk (clabber) is a fair combination with acid fruit or subacid fruit, and that clabber is even a fair combination with dried sweet fruit.

Dr. Vetrano says that occasionally there are sick people with gastrointestinal problems who must temporarily be placed on milk, if they cannot take a fast of sufficient length for complete healing.

More information about the inadvisability of using fermented foods like yogurt, clabber or cheese will be included in a future lesson.

Good, Fair, Poor and Bad Combinations

When we say that foods are fair combinations, this means that they are permissible for those with unimpaired digestions. Good combinations are good for the weakest digestion.

Poor combinations should never be employed, unless, perhaps, they are used occasionally by people with the best digestions. Some combinations are so bad that no one should ever use them.

Examples of these precepts will be given in Lesson No. 23.


The Crux Of Food Combining

If we want to eat several foods at the same meal, it would seem logical that trouble could be avoided, or at least minimized, by ingesting together those foods which are compatible; that is, those which require approximately the same conditions for digestion—including length of time, type of enzymes and digestive juices, and degrees of alkalinity or acidity.

When foods are eaten in incompatible combinations and fermentation results, alcohol is produced in the digestive tract, with the same consequences as imbibing it and with the same potential for liver damage.

The existence of such a still in your body may not be illegal, but it is certainly contrary to the laws of

It is important to remember that all of the senses have a role in digestion. Seeing, smelling, touching, tasting—and even thinking about food—all help in sending the proper signals for the secretion of the digestive juices and their adaptation to the character of the food.

Complicated mixtures of food interfere with this process of digestion, make it less efficient and may cause digestive problems. When we compound the problem by adding seasonings, the true taste of the individual foods is further disguised. This makes it extremely difficult for the digestive system to supply secretions that can cope with such meals and digestion is inhibited and impaired.

The glands react to the foods eaten to the best of their ability. They interpret the signals they receive and supply the best secretions they can muster to preserve the health and the integrity of the organism. When a saturation point is reached, due to continuous bombardment from intolerable food combinations, the ability of the overworked digestive system to make the necessary adaptations is reduced or destroyed, and disease is the result.

Optimal digestion requires that we eat in such a way as to offer the least hindrance to the work of digestion by making the best use of our knowledge of the chemistry and physiology of digestion and of the limitations of the human digestive system.

Raw, fresh, whole, ripe fruit; chlorophyll-, vitamin- and mineral-rich raw, leafy green vegetable, sprouted seeds and raw, unsalted nuts and seeds are essential and valuable—they are the best of foods. Eat them in accordance with food-combining rules, masticate them thoroughly, don’t complicate them with oily dressings, and your body will easily accommodate this food program and progress toward optimal health.

People with serious digestive problems should consult a Hygienic professional and probably undertake the healing that only a prolonged, supervised fast can produce. Afterwards, they too can look forward to utilization of the Hygienic food program on their way to better health.

Dr. Shelton’s Original 9 Food Combining Rules

  1. Never eat carbohydrate foods and acid foods at the same meal.
  2. Never eat a concentrated protein and a concentrated carbohydrate at the same meal.
  3. Never consume two concentrated proteins at the same meal.
  4. Do not consume fats with proteins.
  5. Do not eat acid fruits with proteins.
  6. Do not consume starches and sugars together.
  7. Eat but one concentrated starch at a meal.
  8. Do not consume melons with any other foods.
  9. Milk is best taken alone or let alone.

Food Combinations Discussed in This Lesson

  1. Acid-carbohydrate combinations.
  2. Protein-carbohydrate combinations.
  3. Protein-protein combinations.
  4. Protein-fat combinations.
  5. Fats in combination with other foods.
  6. Acid-protein combinations.
  7. Sugar with starch, protein and acid fruit.
  8. Starch-starch combinations.
  9. Acid fruits with subacid fruits.
  10. Subacid fruits with sweet fruits.
  11. Fruits with vegetables.
  12. Salads with most foods.
  13. Melons best used alone.
  14. Sprouts—Combinations.
  15. Milk, Yogurt, Clabber—Combinations.

Question & Answers

I've heard that food combining is an individual matter. Why can't I ignore it unless and until I have symptoms?

That's the rationale of many people, especially people who stay on conventional diets and eat junk foods. Is it better to avoid damage to your body, or would you rather wait until damage is done, and then try to correct it? Most people already have damaged their bodies long before symptoms appear. It would be much more prudent and sensible to take the best possible care, as soon as you can, of the only body you will ever have in this life, rather than to wait until the road back is long and arduous, and when you would probably have to start with a prolonged fast.

You say an occasional deviation is not too important. How often is occasional?

"Occasional", or infrequent, means different things to different people. A man once said to me, "I eat meat occasionally," and when I asked him how often, he said he eats it once a day. If you do something unwise even once a week, I would call that regularly rather than infrequently. Once a month is less frequently, of course, and might be tolerated fairly well by a healthy body. Actually, the degree of harmfulness of a dietary indiscretion depends on the extent of your deviation and the state of your health. Are you speaking of bending the food combining rules, or do you mean going to a restaurant and gorging on a conventional meal? And, what is even more important, can you afford to deviate? If you are having problems, you would be foolish to do things that can only make those problems worse. For most people who feel they can "afford" to "deviate" "occasionally", it would be best to save such deviations for occasions when they find themselves in unusual situations when such a choice is the lesser evil.

You say not to have more than one concentrated food (protein, starch, sweet fruit) at a meal. Is it all right to have some meals without any concentrated food?

Yes, an excellent choice for the first meal of the day (for most people) is melon or juicy fruit only. Yet, some concentrated foods, especially concentrated proteins, have a place in the food program (See Mono Diets, Lesson No. 23). Starch meals are less important, and dried sweet fruit should be used sparingly. Including concentrated protein foods (usually nuts and seeds) in some of the meals enables the body to obtain a balance of the nutrients it needs. (See sample menus, Lesson No. 23)

I seem to lose weight on an all-raw-food diet, but hold a better weight if I eat some cooked food.

Usually, persistent adherence to an all-raw-food diet eventually results in improvement of assimilation, and one gradually puts on, and retains, more weight. However, if you have a tendency to be thin, or if some impairments cannot be completely overcome, you may have to settle for a leveling off at a weight lower than you prefer. If you feel well, the best thing to do is ignore your weight. In some instances, for emotional or physical reasons, it may be advisable to use a small percentage of cooked food. But most people will be much better off if they can decide to stay with an all-raw-food diet. Those who are convinced that they maintain better weight, feel better or have more energy if they use some cooked starches, legumes or grains, will probably be happier on an 80-90 percent raw-food diet.

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