Hay’s separation diet goes back to the US surgeon and general practitioner William Howard Hay (1866-1940). Hay suffered from a kidney disease that was incurable at the time, and he supposedly cured it with his new nutritional concept. In the German-speaking countries the Haysche separation food was made well-known particularly by the physician Ludwig Walb (1907-1992). Today, internist Thomas Heintze, an associate of Walb, continues the work. Walb and Heintze have adopted Hay’s recommendations for the most part, but have also modified some of them. The alternative form of nutrition “Trennkost” probably has the most followers in Germany after the vegetarian diet. Their number is estimated at 1 to 1.5 million.
Principles and goals
According to Hay’s theory of the chemical laws of digestion, carbohydrates and proteins (protein) cannot be optimally broken down and absorbed at the same time in the human digestive tract. The resulting prolonged residence time of the food pulp in the digestive tract leads to increased fermentation and acid formation, which in turn results in “gastrointestinal autointoxication” and “hyperacidity”. Therefore, the best-known basic principle of the Food Combining Diet is the separation of carbohydrate-rich and protein-rich foods within a meal. Furthermore, according to Hay, the usual “Western” mixed diet causes “overacidification” (acidosis) of the body. This, according to him, is the main cause of all diseases and, in addition, it also affects the mind, causing slow thinking, poor judgment, weakness of thought, lack of concentration and pathological fatigue. Hay blames “hyperacidity” on excessive consumption of proteins and refined and denatured carbohydrates, delayed digestion, and improper dietary composition. To maintain acid-base balance, Hay recommends a diet consisting of 80% base-forming foods and 20% acid-forming foods. Heintze recommends a ratio of 75% to 25% in terms of base-forming and acid-forming foods. The base-forming foods should be consumed predominantly raw, since the protective substances they contain are destroyed during processing. In addition, raw vegetables and whole grain products should stimulate intestinal activity. In addition, foods should be organically grown whenever possible, contain no preservatives, colorings, sweeteners or flavorings, and be eaten fresh, in their natural state or prepared in a way that preserves their value. In summary, the goals of Hay’s Food Combining Diet, which is primarily health-oriented, are:
- Prevention of diseases
- Therapy of diseases, such as rheumatism, colitis.
- Creating optimal conditions for the digestive enzymes
- Preventing the “overacidification” of the body
- Increasing the viability
Operating principle
Several studies in humans have shown that consumption of a meal simultaneously rich in carbohydrate and protein does not prolong the passage time of the food pulp in the gastrointestinal tract, does not cause intestinal autointoxication due to fermentation, fermentation or putrefaction, and does not otherwise lead to disturbances in the digestive process. Thus, Hay’s rationale for separating carbohydrate-rich and protein-rich foods in a meal is scientifically refuted. Moreover, the fact that breast milk, the only food consumed by infants, contains both carbohydrates and proteins also argues against the thesis that humans cannot optimally utilize carbohydrates and proteins at the same time. However, there is evidence that the separation of carbohydrate- and protein-rich foods may make physiological sense in terms of postprandial (“after-meal”) insulin secretion. In a study involving 30 obese women, eating a separation diet produced significantly more favorable fasting insulin levels after 12 weeks, as well as an average 2 kg greater weight loss. The influence of food on the acid-base balance is well known. According to the current state of science, a long-term excessive acid load is probably associated with health risks. However, the thesis that a disturbance of the acid-base balance is the main cause of all diseases is not true.Acids and bases are constantly produced in the body. These must be in balance so that all metabolic processes can run normally.The formation of acids or protons (H+) occurs mainly through the degradation of sulfur-containing amino acids (methionine, cystidine), cationic amino acids (lysine, arginine) and phosphorus-containing compounds. In contrast, the metabolism of anionic amino acids (glutamate, aspartate) and the degradation of organic acid salts (lactate, citrate, malate) lead to the formation of base equivalents (hydroxyl ions, OH-). With the usual protein-rich mixed diet, which is at the same time relatively low in organic acids of plant origin, about 50 mmol protons are formed net per day. However, the body’s excretion capacity for acids and bases, especially via the kidneys, is many times higher, so that the excretion capacity cannot be exhausted even by an extremely unbalanced diet. It is still largely unknown what role the connective tissue plays in the regulation of the acid-base balance. Disorders of the connective tissue metabolism are responsible for a number of diseases, especially vascular diseases and rheumatic complaints. The theory is that excess acids are temporarily or permanently retained in the connective tissue during transport from the cells to the blood and vice versa. The resulting latent acidosis or tissue acidosis is in turn said to result in various metabolic disorders. However, scientific proof for this thesis has not yet been provided.
Implementation
Food selection
Hay describes a diet of raw vegetables, fruits, and nuts as ideal. Walb and Heintze refer to the whole-foods orientation chart for food choices.Milk can be used in any form, although it is said to flush out toxins when eaten with acidic fruits and vegetables, especially in the morning. Cheese, as a strong acidifier, should be consumed infrequently. For fats, cold-pressed vegetable oils rich in polyunsaturated fatty acids should be preferred, as well as unbrowned butter and fresh cream. Salt and hot spices should be used only very sparingly. Fresh garden and wild herbs, on the other hand, can be used abundantly. Consumption of high-energy alcoholic beverages should be kept to a minimum (e.g., 1 glass of beer/day, ½ glass of wine/day), with beer going with the starch meal and wine going with the protein meal. Refined, denatured, and highly processed foods, especially those containing additives, should be avoided. Pork and legumes are completely discouraged. Other foods not recommended according to Hay’s Food Combining Diet are:
- White flour, white bread, white flour pasta, polished rice, sago, peanuts, white sugar, sweets, jam, jelly, preserves (= predominantly carbohydrate foods).
- Legumes, hydrogenated fats, finished products such as mayonnaise, black tea, large amounts of coffee (max. 2 cups / day), cocoa, vinegar essence (= neutral foods).
- Pork, raw protein, fatty sausage, smoked or cured meats, preserves, rhubarb (= predominantly protein foods).
Special features
Guidelines of Hay’s separation diet according to Heintze (2005) are:
- Separation of protein-rich foods from carbohydrate-rich foods within a meal.
- Classification of foods into the 3 groups concentrated carbohydrate-rich, neutral, and concentrated protein-rich (see Table 1).
- All neutral foods can be combined with both high-carbohydrate and high-protein foods
- Consumption of only one type of protein (meat or fish, max. 60-100 g/day) per meal.
- Classification of foods into alkalizers and acidifiers (see Table 2).
- The ratio of base-forming and acid-forming foods should be 75% to 25%.
- The protein meal should be taken at noon, the carbohydrate meal in the evening
- Between the individual meals should be breaks of three to four hours
- Taking the last meal not after 6 p.m.
- Use of natural and, if possible, regional and seasonal foods from organic farming
- Consume only as much as is necessary to sustain life
- Eat slowly and at rest, as well as chew thoroughly.
- For the purpose of rapid satiety, a portion of raw vegetables or salad should be consumed before each main meal
Tab.1: Classification of food according to Walb and Heintze
| Predominantly carbohydrate-containing foods | Neutral foods | Predominantly protein hydrate foods |
| All cerealsz. B. Wheat, spelt, rye, barley, oats, corn, brown rice. | The following fats Vegetable oils and fats, cold-pressed oils from seeds and sprouts, such as sunflower oil or walnut oil, butter | All cooked meats (except pork)e. E.g. roast, steak, minced meat dishes, rolled roast, goulash, beef boiled ham. |
| All whole grain productsz. E.g. wholemeal bread, wholemeal rolls, wholemeal pasta, wholemeal semolina, wholemeal cake. | All acidified dairy productsz. E.g. curd cheese, kefir, buttermilk, whole milk yogurt, sour cream, sweet cream, heavy cream cheese (> 60 % fat i. Tr. ), cream cheese | All cooked poultry varietiesz. E.g. turkey breast, grilled chicken, poultry sausage. |
| The following vegetablesPotatoes, Jerusalem artichoke, batata, salsify. | The following vegetables and lettuceArtichoke, eggplant, leaf lettuce, cauliflower, broccoli, watercress, chicory, Chinese cabbage, lamb’s lettuce, fennel, kale, cucumber, carrot, kohlrabi, pumpkin, dandelion, Swiss chard, bell bell pepper, parsnip, hot peppers, radish, radish, Brussels sprouts, beet, red cabbage, white turnip, sauerkraut, celery, asparagus, spinach (raw), rutabaga, tomato (raw), white cabbage, savoy cabbage, zucchini, onion | All kinds of cooked fishz. B. trout, halibut, herring, cod, salmon, mackerel, plaice, pollock, tuna, shellfish and crustaceans |
| The following fruitsFig, date, banana, non-sulfurized dried fruits such as raisin, apricot, plum. | The following other foodsyolk, ripe olives, agar-agar, nuts, almonds, blueberries, vegetable broth with granules | The following other foodsCheese up to 55% fat in dry matter such as Harzer, Tilsiter or Gouda, milk, eggs, tofu, tomato (cooked), spinach (cooked) |
| The following sweetenersbees honey, maple syrup, apple and pear syrup, frutilose. | The following spicesFull sea salt, herb salt, celery salt, garlic, paprika, nutmeg, bell pepper, curry, basil, wild and garden herbs | Acidic fruit that can be combined with high-protein foodsRenary fruit, pome fruit, stone fruit, citrus fruit, tropical fruit. |
Table 2: Classification of foods into alkalizers and acidifiers.
| Alkalizing foods | Acid-forming foods |
| Vegetables, root vegetables, vegetable fruits, leafy vegetables, salads | Animal protein such as meat, fish, sausage, offal |
| Soybeans, soy milk, coconut milk. | Vegetable protein such as corn, rice, wheat, rye, oats, barley, amaranth, whole grain flours |
| Milk, whipped cream | Extract flours in white pastry, bread, pasta |
| Boiled potatoes | Dairy products such as cottage cheese, cheese |
| Chestnuts | Industrial food, ready-made food, canned food, ketchup, ready-made salad dressings |
| Ripe fruit, dried fruit | Drinks such as cola, lemonade, syrup, juices, cocktails |
| Almonds, almond milk | Refined oils and fats |
| Wild herbs such as stinging nettle, dandelion, arugula, purslane, wild garlic | Factory sugar, fructose, confectionery, chocolates. |
| Aromatic herbs such as cress, chives, chervil, coriander, mint, marjoram, thyme. | Citrus fruits like grapefruit |
| cold pressed vegetable oils, olives | stimulants such as coffee, alcohol, nicotine |
Nutritional evaluation
Advantages
The high proportion of plant-based foods, with a preference for whole grains and minimally processed foods, can ensure a high intake of vitamins, minerals, and fiber. The nutritional errors often associated with an average mixed diet, such as excessive fat, sugar and salt consumption, are avoided. In addition, due to the low consumption of meat, the intake of saturated fatty acids, cholesterol and purines is low. The required interval of 3 to 4 hours between meals results in 4 to 5 meals per day, as also recommended by the DGE. In addition, Hay’s Food Combining Diet is relatively low in energy due to its lacto-vegetable focus, which is advantageous with regard to a desired weight reduction.
Disadvantages
Separating carbohydrates and proteins within a meal can sometimes be difficult in practice. In addition, the nutritionally valuable legumes, which are rich in carbohydrates and protein, are not recommended in Hay’s separation diet. The separation principle also results in preventing optimal complementation of plant and animal foods, since some carbohydrates together with protein foods contain a biologically valuable protein. Such combinations are, for example, cereals with milk (muesli) and potatoes with eggs.The practical implementation of the recommendation with regard to base-forming and acid-forming foods can have an unfavorable effect on food choices, so that cereals and cereal products, dairy products such as cheese, fish and meat are consumed only in small quantities. This, in turn, risks insufficient intake of some micronutrients such as vitamin B complex (especially folic acid), vitamin D, calcium, magnesium, iron, selenium, iodine, or omega-3 fatty acids.
Contraindications
Hay’s Food Combining Diet is of limited use, especially for children, pregnant women and nursing mothers, due to the risk of deficiency of vitamin B complex (especially folic acid), calcium, magnesium, iron, selenium, iodine and omega-3 fatty acids.
Conclusion
In its practical design, Hay’s Food Combining Diet represents a predominantly lactovegetable form of nutrition with moderate fat and energy content and high fiber content, which is partially based on the recommendations of whole-food nutrition. A need-based supply of essential nutrients is possible with a broad selection of foods, so that Hay’s Food Combining Diet is basically suitable as a permanent diet. However, in order to avoid an undersupply of micronutrients, care should be taken to ensure adequate consumption of cereals and cereal products, dairy products and fish. Non-evidence-based studies suggest that Hay’s Food Combining Diet can have a positive effect on various diseases, such as rheumatic diseases, skin diseases, obesity, lipid metabolism disorders or hypertension. However, the positive effects of the Food Combining Diet are probably due to the high-fiber, low-fat, low-meat and low-cholesterol diet and not to the separation of carbohydrate- and protein-rich foods and the high proportion of base-forming foods. In addition, Hay’s Food Combining Diet is based on numerous statements that are false or scientifically unsubstantiated. In addition, the allocation of foods to the groups seems partly arbitrary. For example, cream cheese and cottage cheese are assigned to the neutral foods instead of the protein-rich foods, or tomatoes and spinach belong to the group of neutral foods when raw, but to the group of protein-rich foods when cooked.
