It takes from 24 to 72 hours to digest fish, which contains proteins and fats. Generally, food takes six hours to move through the stomach and small intestine. Nutrients and water are absorbed in the large intestine, and the residue is excreted through the colon and rectum after 24 hours.
The digestion and assimilation of food is a slow process. Carbohydrates are digested quickly, but proteins and fats take longer. Fruits and vegetables take less time for digestion, while fish and meat take longer.
Food must be broken down into simple components for digestion and assimilation to take place. The pancreas, liver and gall bladder help digest and assimilate nutrients from food.