Your gastrointestinal tract (GIT) is the first line of action that comes into play once food is eaten, and this acts like a food processor for digesting, absorbing and assimilating whatever is eaten. The whole process of digestion begins from the moment food enters the mouth, passing through the long muscular tube which comprises the mouth with the salivary glands, stomach, small and large intestines, meandering through the colon, liver, pancreas and the gall bladder. All of these organs are somehow involved in the digestive process once food is ingested. So you can imagine how important it becomes that the type of food we eat, works in sync with these organs in their own respective areas. The GIT has a sensory mechanism by which it reacts to the type of food ingested or even in the form or combination it is ingested, e.g. a carbohydrate based food with fat one or a protein based one etc. By virtue of this sensory mechanism the GIT can reject or react to the food through vomiting, allergic reaction, nausea or diarrhea.