Disintegration of food in the gastrointestinal tract: what do we know and where are the gaps?
Résumé
Digestion provides nutrients and energy essential to the survival and growth of the organisms. It
also leads to the release of components (bioactive peptides, fatty acids, minerals…) that can have a
positive or negative effect on human health. So far, the digestive tract has very often considered as
a black box with a poor understanding of the mechanisms of food breakdown and more research is
needed on this topic if we want to better understand the effect of food on human health. One of the
key step of the gastrointestinal digestion is the gastric phase. When the bolus enters the stomach, acid
and digestive enzyme secretions will initiate hydrolysis of the macronutrients. Gastric emptying will
be modulated by the caloric content of the meal and its osmolarity. Recent evidences have shown that
the structure the food will adopt in gastric conditions is also an essential factor and more research
is needed to determine how this structure is formed, how the digestive enzymes will diffuse, get
access and hydrolyse their targets… We also need to get a better understanding on to what extent
stomach contractions affect the breakdown of food matrices of different viscosities and structures.
After gastric digestion, food constituents will be transferred into the small intestine where most of
the dietary proteins and lipids will be digested thanks to highly efficient digestive enzymes (trypsin,
chymotrypsin, pancreatic lipase) and bile salts and then further absorbed. More research is needed
in order to determine the exact protective role played by the mucus layer, the structure needed for a
nutrient to be absorbed, the interactions that occur between nutrients in the lumen, the half-life of
food constituents when they will enter the bloodstream… Finally, undigested dietary components
will reach the large intestine. We still don’t know precisely the relative amount of food proteins and
lipids that will reach the colon, how it will be handled and affect the intestinal microbiota and what
will be the consequences for human health. Although the whole digestive process has been studied
for years, gaps in knowledge on the precise mechanisms of food disintegration in the gastrointestinal
tract are still numerous and deserve a better attention if we want to clarify the impact of food on
human health.