Vegetable proteins are less assimilated by the intestine, according to a study

The proportion of people adopting a meatless diet is gradually increasing. Out of ecological principle, out of respect for animal welfare, to limit their expenses or to preserve their health, these people are turning to vegetable alternatives, based on soy and wheat proteins. However, the nutritional quality of these products is still the subject of debate within the scientific community. A new study reveals that the proteins in plant substitutes are not as well assimilated as those in meat.

According to an Ifop survey conducted in 2020 on behalf of FranceAgriMer, 68% of respondents believe that we consume too much meat in France and 56% believe that meat production has a negative impact on the environment. However, only 2.2% of those surveyed said they had adopted a meat-free diet. However, almost a quarter of them have voluntarily reduced their consumption, thus becoming flexitarians. But reducing your meat intake or not eating it at all means you’re cutting out an important source of protein from your diet.

However, proteins are essential for the body: not only do they play a structural role (at the level of muscles and skin), but they are also involved in a large number of biological functions, such as immunity, digestion or transport. of oxygen Therefore, a healthy adult under 60 years of age should consume 0.83 grams of protein per kilo of body weight every day, according to ANSES. Plant-based protein foods have become common, but it is not clear how much of this nutrient reaches human cells.

The meat substitutes considered “healthier”

Apart from animal proteins (found in meat, fish, eggs and dairy), the plant foods richest in protein are oilseeds, legumes and cereals. Therefore, foods sold as meat substitutes are often made from soy or wheat. Sausages, minced steaks, nuggets, breaded chops now exist in a 100% vegetable version.

To mimic the look and texture of real meat, the botanicals are dehydrated, pulverized and mixed with seasonings. These blends are then heated, moistened and processed through an extruder. Consumers of these products often think that they are healthier than animal meats. And for good reason: consumption of red meat and cold cuts is associated with an increased risk of colorectal cancer. Also, the plants used to make meat substitutes are low in “bad” fats (so-called saturated fats).

However, laboratory tests have shown that the plant proteins in alternatives do not break down into peptides as well as those in meats. Researchers at Ohio State University explored the question: They set out to test whether human cells could take up as many peptides from a meat substitute as the peptides from a piece of chicken.

The substitute was produced by extrusion, using soy protein and wheat gluten. They then compared the physicochemical properties, digestion in vitro and the cellular absorption of the peptides released by each of these two foods. The results show that the proteins of the vegetable substitute are not as accessible to the cells as those of the meat.

Larger and less soluble proteins

In appearance, the two materials were similar: when cut, the meat substitute had long, stringy pieces, like real chicken. ” The meat analog showed greater hardness, but a lower degree of texturization than the chicken. “, specify the researchers. The team then cooked pieces of these two “meats”, then ground them before breaking them down using a human digestive enzyme, to simulate the processes of chewing and digestion.

A meat substitute (left) resembles chicken meat (right), but its proteins are not as well absorbed by human cells. © J.Agric. food chemistry

Tests in vitro they were then carried out on cultures of Caco-2 cells, used as models of intestinal epithelial cells, to estimate the amount of peptides that cross this dummy intestinal wall during transit (set here at 4 hours). The researchers report that no cytotoxicity or inflammatory response was observed, both in the case of the surrogate and in the case of the chicken. However, the surrogate showed decreased peptide permeability across Caco-2 cells, they note.

The substitute peptides had a higher molecular weight and were less soluble in water than those from chicken. Because of this, they were also not taken up by the cells. The intestinal cells had absorbed about 2% less protein in the case of the substitute. The difference may seem small, but the researchers point out that they only used a simplified model of the intestinal wall here: in the real intestine, peptides must also pass through a layer of mucus before reaching the epithelial cells; assimilate into reality.

According to the team, these results could eventually be used to develop healthier products. In particular, it would be necessary to identify ingredients that could help stimulate the absorption of peptides from plant-based meat substitutes. In the meantime, these meat substitutes remain a good source of protein and can be used as part of a balanced diet, the researchers conclude.

Source: D. Chen et al., J. Agric. food chemistry