There is no exact science to find out how long it will take for your body to digest food. Hydration and digestive health affect how long it takes your body to digest food. Food moves faster through the digestive track when the body is hydrated. You can estimate how long it will take based on the make-up of the food you eat. For most healthy adults, digestion takes between 24 and 72 hours. Carbohydrates digest faster than proteins, and proteins faster than fats.
Carbohydrates, or sugars, are the main source of energy for your body, which is why they are the first to be absorbed. There are two types of carbohydrates: simple carbohydrates and complex carbohydrates. Fruits and vegetables are simple carbohydrates that process in only one step. Enzymes turn sucrose into fructose and glucose, which is absorbed into the blood stream in the small intestine. Complex carbohydrates, like rice and oatmeal, take longer to digest. In two steps, they are broken down in the mouth and stomach and then into absorbable particles in the small intestine. It takes approximately four to five hours for the stomach to empty completely into the small intestine. The enzyme insulin helps digest sugars; patients with diabetes need to ingest insulin to digest carbohydrates in four to five hours.
Proteins support the building and rebuilding of muscles and tissue. Protein-rich food include meat, eggs, beans and nuts. In a well-balanced meal containing carbohydrates, protein and fat, the protein and the fat will slow down the overall time it takes to digest your food. In the mouth and stomach, enzymes have already started to break down protein molecules. Food can spend up to four hours in the small intestines. In that time, proteins are broken down. Proteins can have between two and 200 amino acids. The more amino acids, the longer it takes to break down the protein.
It takes eight hours for food to pass from the mouth to the large intestine or colon; fats take between six and eight hours. Examples of food containing fats include meat, nuts, oils and avocados. They are the most complex of the molecules. They protect cells, prevent inflammation and are essential for brain development. In addition, they store extra energy. Fat molecules are made of fatty acids -- either saturated or unsaturated. Bile from the liver breaks the fats into droplets small enough to be broken down by enzymes and absorbed. Patients with gallstones that block the flow of bile to the small intestine will have trouble digesting fats.
Alcohol enters the bloodstream first because there is nothing to break down. To slow down the absorption of alcohol, drink it with a meal. Hard liquor is naturally carbohydrate-free. The carbohydrates in beer and wine are residual from the fermented food used to make the drink. For example, a 147ml. glass of wine contains 5 grams of carbohydrates and 13 grams of alcohol.
Fibre is not digested by the body, so it spends the longest time in the digestive tract. Once carbohydrates, protein and fats are absorbed in the small intestine, fibre, waste and water move to the large intestines. Unless you have a digestive disorder like Irritable Bowel Syndrome, the water is reabsorbed. Fibre is important because it helps move waste along the large intestine, preventing constipation.