Why protein diets make you lose weight

Why it matters

The gut microbiota plays many roles in our health, and in particular in obesity. The microbiota of obese people is often unbalanced. Hence the idea that the intestinal flora is involved in controlling an individual’s weight.

Diets high in protein and low in carbohydrates, such as the new Atkins diet, have been shown to be effective for weight loss. But what is the mechanism that explains this weight loss? Is this linked to changes in the intestinal microbiota? This is what scientists from the University of California at Los Angeles sought to find out in a study published in the journal Nutrients.

The study

For eight weeks, 80 overweight or obese people followed a low-calorie diet, either with high protein (30% of energy intake in protein, 40% in carbohydrates and 30% in fat), or with the usual protein intake (15% protein, 55% carbohydrates and 30% fat).

Results: the high-protein diet allowed more diversity of intestinal flora than the diet with 15% protein. By examining the changes in microbiota compared to the initial situation, the researchers also found that the high-protein diet modified the composition of the microbiota more than the other.

However, both diets allowed an enrichment of bacteria Akkermansia and bifidobacteria, and a reduction in Prevotella.

In the microbiota, the predominant genus of Prevotella East Prevotella_9. This bacteria is associated with obesity, diabetes and the progression of fatty liver disease. The disappearance of this bacteria thanks to low-calorie diets could partly explain the benefits of these interventions.

Furthermore, with the high protein diet, there was also:

• a decrease in another bacteria of the genus Prevotella : Prevotella_2. This bacteria is associated with cardiovascular risk. This could explain why a high protein diet is more favorable for the heart,
• an enrichment of bacteria Gemella : these bacteria are normally present at the beginning of the gastrointestinal system, and less in the colon. The diet must have allowed an extension of the colonization zone of the bacteria. But the role of this bacteria in obesity is unknown.

Bifidobacteria are often considered probiotics. In their discussion, the authors mention another interesting study on people with a particular variant of the LCT gene which allows them to still have lactase (the enzyme allowing the digestion of lactose, the sugar in milk) in adulthood. These people have more bifidobacteria in their microbiota. In this experiment, more than 500 people with this allele followed weight loss diets. It appeared that it was with a high-protein diet that these people lost the most fat. Bifidobacteria are therefore perhaps a target of high-protein diets.

In conclusion, weight loss has an effect on the composition of the intestinal microbiota which could explain the benefits of high-protein diets.

In practice

It is better to consult your doctor or a health professional before starting a protein diet because it can have long-term consequences, particularly on kidney health, if it is not followed properly. The Atkins diet remains the most studied diet and with the highest level of evidence. But it is also possible to change the composition of the microbiota in order to promote weight loss without resorting to a protein diet.