The Ultimate Guide to Digestion: Understanding It Better to Improve It

Digestion encompasses all the transformations that food undergoes in the human digestive tract. The digestive tract includes the mouth, esophagus, liver, stomach, gallbladder, small intestine, large intestine, and anus. Indeed, when we consume food, through the process of digestion, this food is transformed into nutrients and waste. The nutrients are used by the cells, and the waste is evacuated through the anus and kidneys.

How does digestion work?

Digestion is the transformation of the food consumed and takes place in several stages. These include:

The mechanical digestion stage

This begins with chewing. At this stage, the food is ground and reduced to small pieces in the mouth under the action of the teeth and saliva. The chewed food is sent to the pharynx. At this level, under the effect of the enzyme called amylase, the chemical transformation begins and continues its circuit towards the esophagus to land in the stomach, thanks to the muscular contraction of the digestive system.

The stage of gastric digestion

This is the stage where the small intestine and stomach work at full capacity to recover all the nutrients the body needs from the consumed food. In the stomach, the food, under intense mixing action, is transformed into a homogenized slurry called chyme. Gastric juice is involved in the breakdown of the proteins contained in the food to obtain amino acids. Then, the result is transported to the small intestine for another stage of digestive transformation. The transition from the stomach to the small intestine can sometimes take time if you have consumed a rich and copious meal. It is important to avoid intestinal overload at all costs.

The intestinal digestion stage

In the small intestine, under the action of other types of enzymes, the chyme is further broken down in the duodenum. Nutrients needed by the cells of the human body are extracted in the small intestine.

At the intestinal digestion stage, the following are involved :

• Pancreatic juice (which contains enzymes such as amylases, lipases, peptidases, and proteinases),
• Intestinal juice ( necessary for the breakdown of large molecules by enzymes such as sucrases and phosphatases)
• Bile (a unit of digestive juice that absorbs fats).

Bile, stored in the gallbladder, is a byproduct of liver secretion and contains bile salts. These salts facilitate the emulsification of all the lipids contained in the food to be digested.

The colonic digestion stage

The colon is the receptacle of intestinal digestion. During intestinal transit (which lasts between 6 and 12 hours, nutrients are absorbed by the cells, and the rest is conveyed to the colon. In the colon, a viscous liquid (which is a collection of fiber or animal residues) is mixed with the remains evacuated in the colon. The bacteria in the colon transform the residues that have not been digested into fecal matter, which will be evacuated through the anus. When the stool is evacuated, digestion is complete.

Digestion time varies depending on several parameters. On average, this time is estimated at 24 hours. In short, it takes the human body 24 hours to completely transform food into nutrients and waste.

The digestive cycle path in duration is as follows:  

• A few seconds: In the esophagus, it takes just a few seconds for the food bolus to be transformed and transported to the stomach.  

• 4 hours: Digestive transformation in the stomach lasts approximately 4 hours. In the stomach, enzymes and gastric juice are used to complete gastric digestion. The chyme is then transported to the small intestine.  
• 4 hours: When the chyme reaches the small intestine, pancreatic juice, intestinal juice, and bile must act to transform the chyme into nutrients and viscous liquids. The transformation takes an average of 4 hours. After 4 hours of transformation, the large intestine takes over.  
• 4 p.m.: The large intestine takes longer to digest the processed food that has reached it. It takes an average of 16 hours to complete its digestive work. The anus extends the terminal phase of the large intestine: digestion ends when the human evacuates the stool, which represents waste that the body does not need.

Digestion time in infants

The digestion time for infants cannot be the same as that of an adult or a baby. First, it is useful to remember that an infant is between 30 days and 23-30 months old. Beyond that, they are considered babies.  

If it is recommended to feed the infant exclusively with breast milk until 6 months of age, it is primarily to facilitate the infant’s digestion and especially to educate the digestive system to function normally.

An infant’s digestion time will depend on their age. Between 0 and 6 months, infants may require breastfeeding or formula every 3 or 4 hours. Breast milk is digested more quickly (on average, 3 hours) than formula, which is digested every 4 hours. Beyond 6 months, an infant’s digestive system begins to regulate, particularly with the introduction of new food categories.  

Digestion, therefore, takes place on average between 6 and 12 hours per day. This is because the stomach takes up more space and more time to process food.

Parents are therefore advised to pay particular attention to their infant’s digestion. Between vomiting, bloating, and repeated bouts of colic, infants sometimes experience digestive problems.

Some foods are digested more quickly than others. That’s why dietitians recommend specific food categories for fast and efficient digestion.

Fruit juices and vegetable juices

It is observed that on average, it takes 15 minutes for a fruit juice to be completely digested. Indeed, fruit juices and vegetable juices – once introduced into the mouth – do not undergo 100% of the digestive mechanism. Be careful: they go through the entire digestive cycle, but the duration of assimilation and digestive metabolism is reduced.

Digestion of raw fruits

When you consume whole fruits raw, cooked, or pre-cooked, digestion takes longer than juices.

• Cucumber, pepper, and spinach take at least 30 minutes to digest.
• Apples, pears, and bananas take at least 45 minutes to digest.
• Carrot or beetroot takes at least 60 minutes to be metabolized or assimilated.

Note that when these fruits – even if they are in raw form – are at least crushed before being eaten, digestion time is reduced.

The time for digesting legumes, cereals, and dried fruits

• The digestion of legumes, cereals, or, for example, artichokes takes on average 90 minutes to complete.
• The digestion of dried fruits and assimilated fruits (especially pumpkin seeds, sunflower seeds, or sesame seeds) takes at least 2 hours.

Digestion time of animal products

Dairy products in general, meat, and fish require at least 4 hours of digestion time.

For good digestion, it is important to favor lacto-fermented foods. Indeed, this type of food contains probiotics and prebiotics, which are nutrients that facilitate good digestion and a fairly dynamic intestinal transit. Among the lacto-fermented foods, it is necessary to recognize:

• vegetables,
• sourdough bread
• yogurts

The fiber in fruits is softened when the fruit is cooked. This fiber helps with digestion.

Bad foods for digestion

When food takes longer to digest, it is considered bad food because all the body’s organs have to work beyond their capacity. These foods sometimes damage certain organs, such as the liver, for example.

Foods that make gastric emptying difficult include:

• Cooked fats
• Meats

• Some fried foods
• Alcohol…

These foods—and many others—make digestion difficult (4 hours of digestion time). Exercising and exercising can help with the digestion of these foods.