Food digestion times can vary, even considerably, from individual to individual, depending, for example, on the ability to chew slowly, gastric acidity and intestinal motility.
For non-athletes, however, consuming foods that are not easily digestible in large quantities can cause unpleasant sensations in the stomach and intestinal tract (heaviness, acidity, cramps, etc.)
In general, digestion times increase proportionally to the fat content of food, while they decrease when food is carefully chewed, properly cooked or has a liquid consistency. Among the various cooking methods, the most challenging from a digestive point of view are frying and grilling (in particular if there are carbonized parts).
To get an idea of the importance of adequate chewing, just think that fruit and vegetable smoothies are digested much more quickly than the whole raw material. Obviously there are exceptions; whole milk, for example, requires quite long digestion times despite being liquid.
Also, food combinations should not be underestimated, since digestion times become longer when different food categories are consumed in the same meal. On an empty stomach, for example, water leaves the stomach almost immediately, while when it is consumed during meals it remains for a long time. If drunk in large quantities, it also dilutes gastric juices excessively, increasing digestion times. A similar argument can be made for fruit that - if consumed at the end of a meal as usual - prolongs the stay of the bolus in the stomach (not by chance it is recommended as a snack and for breakfast; for further information, see the principles of the dissociated diet). The exception that confirms the rule is given this time by pineapple and papaya, rich in proteolytic enzymes such as bromelain and papain, which facilitate the digestion of proteins.
Finally, it is logical to expect that quantities also greatly influence digestion times; a chocolate, for example, is digested much more quickly than a chocolate cake.
As an indication light meals require gastric digestion times of 2 or 3 hours; normal meals remain in the stomach for 3 or 4 hours, while particularly elaborate menus take up to 5 or 6 hours before arriving in the small intestine.
Gastric digestion times of some foods (indicative data)
| Food | Quantity | Food | Quantity |
| 20 minutes - 2 hours | 2-3 hours | ||
Beer Broth without additions Cocoa without additions Coffee without additions Boiled milk Tea without additions Eggs with milk Light wine Vegetable or fruit smoothies Watermelon / melon Fruit Skimmed milk | 200 g 200 g 200 g 200 g 100 - 200 g 200 g 100 g 200 g 200 g 200 - 400 g | Beer Cocoa with milk Coffee with cream Boiled milk | 300 - 500 g 300 g 200 g 300 - 500 g |
| 3 - 4 hours | 4 - 5 hours | ||
Beef Ham Boiled pigeon Roast pigeon White bread Boiled rice Boiled carrots Salted caviar Boiled cabbage Boiled carrots Boiled spinach Cucumbers in salad radishes apples Jams Banana | 250 g 160 g 230/260 g 195 g 150 g 150 g 150 g 12 g 150 g 150 g 150 g 150 g 150 g 150 g 150 g 150 g | Salted anchovies Roast hare Smoked language Roasted goose Roasted partridge Roast pigeon peas Roasts Lentils Fries Sauerkraut Fat meats Lard, butter | 200 g 250 g 250 g 250 g 250 g 210 g 200 g |
Always as a general indication, the ingested food reaches the final stretch of the small intestine within 6-8 hours; the elimination of waste and indigestible residues starts about 24 hours after swallowing and may take a few days to complete.
The average passage time of undigested food residues in the human intestine is 50 hours in humans and 57 hours in women, with wide intra and interindividual variations (minimums well below 20 hours and maximums above 100 hours).
