The theory of food combining is based on the fact that each type of food requires different lengths of time, different enzymes and different pH balances (the degree of acidity or alkalinity of the digestive juices) for proper digestion.
Some foods, like nut and seed proteins, require an acid environment. Other foods, such as starches (winter squash, yams) and acid fruits (oranges, pineapple), break down more easily in an alkaline environment.
Combining foods that require different digestive environments causes indigestion (gas, constipation, diarrhea, nausea, bloating, fatigue) and results in incomplete digestion. Incomplete digestion forces your body to spend more energy creating more digestive enzymes (and even white blood cells), thereby robbing it of the energy it needs to create tissue-building, metabolic enzymes.
For example, many people say that watermelon gives them indigestion. Since watermelon digests in only 20-30 minutes, when it enters your stomach filled with slower digesting food, it gets held up in its digestive process and ferments. This fermentation causes gas and discomfort.
However, watermelon eaten on an empty stomach does not create digestive distress, and because of its rapid transit, your stomach will be free to digest other foods within half an hour. As a result, one of the food combining rules is: Eat melons alone.
Not everyone agrees that food combining is an important issue. For instance, some feel that if you eat primarily enzyme-rich raw food, the food will digest itself making food combining rules unnecessary. Instead, food combining principles are much more relevant when food is cooked because then your body has to work harder to manufacture the necessary digestive enzymes.
It is important to listen to your body. By experimenting with the food combining principles, including single-food meals (mono-meals), you will learn through experience what is best for your own metabolism and digestion.