- Foods with which concentrated protein foods should not be combined:
The first and most important rule of food combining is to avoid mixing of concentrated protein and carbohydrate foods. Protein concentrated foods demand the longest digestive time. Stomach keeps them for hours (usually 3 to 6 hours, based on complexity/type of protein present) until the gastric juices have performed its task. On mixing of concentrated protein foods with starch-concentrated or sugar-concentrated foods, fermentation is likely to occur. Indigestion and gas problem are the common symptoms of it.
Animal-food proteins require very high concentration of hydrochloric acid in gastric juices. The presence of fermented carbohydrates greatly inhibits the gastric digestion of these proteins inside the stomach, leading to the production of more gas and increased discomfort. Eating meat, potatoes, bread and sweets should, therefore, be especially avoided.
- Foods with which concentrated protein foods should be combined:
Animal-food proteins are best digested when eaten with fresh vegetable salad. Vegetarian/primary protein foods such as nuts, seeds, and soybeans combine very well with other options also, like oranges, pineapples, grapefruit or lemons. They are also fairly good with fruits like grapes, pears, apples, apricots, berries or peaches. The presence of vitamin C in them aid in protein digestion.
- Foods with which high-fat content foods should not be combined:
Another important rule of food combining is to avoid mixing of high-fat foods with concentrated proteins. The presence of high fat in food inhibits the secretion of gastric juice through the small wall, thus decreasing the gastric catabolism, by the degree of liquid concentration in the stomach. Also, the fat will remain undigested in the stomach until gastric juices complete their work on the complex protein molecule.
It is important to know that this avoidance rule is primarily for free fats like oil, butter or fat surrounding fried foods, which inhibits the gastric juice secretion by coating gastric mucosa. The fat which is found in the primary protein foods will be held in suspension, awaiting catabolism in the intestine, without impeding gastric action.
- Foods with high carbohydrate content should not be mixed with acidic foods:
Carbohydrates need ptyalin enzyme in the saliva, as the food is chewed. Ptyalin converts the complex starch molecules into simpler sugars. But for proper functioning ptyalin requires a neutral or slightly alkaline surroundings/medium. Eating of acidic foods restricts the functioning of ptyalin.
As a precautionary measure, we should avoid having acidic fruits (mainly citrus fruits) in the same meal containing sweet fruits or starches. E.g. avoid tomatoes with starches like potatoes or bread. Refined sugar products are also considered as acidic inside mouth and in the bloodstream. Sucrose acidifies the saliva often leading to tooth decay.
The best practice of eating is to have a simple one item diet at one time, e.g. fruit meal for breakfast, a starch meal with salad and no- starchy vegetables for lunch, and a protein meal with a salad and non-starchy vegetables for dinner. Otherwise, try to have foods with starches, fats, and sugars with green vegetables which aid in keeping the medium alkaline or neutral during digestion. Similarly, proteins can be taken with acidic fruits and vegetables, as they require an acidic or neutral medium for their digestion.