Probably the first scientific studies on digestion were done by Ivan Pavlov who became famous for his 'salivating dogs'. Pavlov showed that the digestive enzymes released and the amount of acid secreted depends on the type of food.

His experiments with rats showed that starches are digested in about two hours, proteins are digested in about four hours but a protein-starch mixture could still be digesting 13 hours later. With dogs, again the protein-starch mixture took over twice as long compared to the same food consumed separately.

Pavlov also showed that food taken on top (i.e. before digestion has completed) can lead to fermentation. This happens when you eat fruit after a meal; many people say that it gives them gas.

What could account for Pavlov