A protein meal of meat, cheese or eggs, is broken up by the teeth and passed down to the stomach. In response to the arrival of the protein, the stomach lining produces a strong acid, and enzymes which digest protein in acid solution, and a thick sticky mucus to protect the lining of the stomach from attack by its own enzymes. These enzymes snip the long protein molecules in our food into shorter chains and then into individual amino acids.
A meal of protein may take several hours for complete digestion before passing on into the small intestine. Here the stomach acid is neutralised by bile salts from the liver. The pancreas now adds further protein digesting enzymes to complete the digestion of protein and the soup of amino acids is now absorbed through the villi that line the small intestine and are passed on into the blood stream.
A meal of starch is partly digested in the mouth where chewing mixes enzymes in the alkaline saliva with the food. The starch molecule is split into sugar molecules. A starch meal does not stimulate the stomach to produce acid, or protein digesting enzymes, and the food is passed on to the small intestine within an hour. In the small intestine, further enzymes are added in an alkaline solution that complete the breakdown of starches into sugars. These are also absorbed through the villi that line the small intestine and pass into the blood stream.
This system only works efficiently if starch and protein appear as separate meals. The food combining lifestyle puts this scientific knowledge into practice.
If starch is mixed with protein, the enzymes in the stomach are diluted and the stomach feels full for longer because digestion of protein is inefficient. Acid is being produced for every mixed meal, which puts the stomach under stress. The acid has to be neutralised by the bile salts for every meal, which puts the small intestine under stress.