An important rule for food combining is to avoid mixing carbohydrates and acid fruits in the same meal. The starch-splitting enzyme ptyalin in the saliva plays an important role as the food is chewed. It converts the complex starch molecules into simpler sugars. Ptyalin requires a neutral or slightly alkaline medium for proper functioning and this is the normal condition of the saliva in the mouth. However, when acid foods are taken, the action of ptyalin is halted. It is, therefore, necessary to avoid acid fruits in the same meal as sweet fruits or starches. Thus tomatoes should not be eaten with starches especially potatoes or bread. Refined sugar products are also acidic, both in the mouth and in the bloodstream. The acidifying of the saliva by sucrose is one of the main causes of tooth decay. It can also cause severe damage to the digestion. In a nutshell, starches, fats, green vegetables and sugars may be eaten together as they require either an alkaline or neutral medium for their digestion. Similarly, proteins, green vegetables and acid fruits may be eaten together as they require an acid or neutral medium for their digestion. But starches and proteins, fats and proteins and starches and acid fruits should not be eaten together as a general rule, if the best results are required from the ingestion of the food eaten. This in brief is the whole basis for successful food combination.