Changes in the intestinal microbiota would explain the benefits of protein diets on weight.

Why it matters
The gut microbiota plays many roles in our health, especially in obesity. The microbiota of obese people is indeed 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 behind this weight loss? Is it linked to changes in the gut microbiota? This is what scientists at the University of California at Los Angeles sought to know 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 intake of protein ( 15% protein, 55% carbohydrates and 30% fat).

Results: the diet rich in protein allowed more diversity of the intestinal flora than the diet with 15% protein. By examining the microbiota changes from the baseline, the researchers also found that the high-protein diet changed the composition of the microbiota more than the other.

However, the two regimens allowed an enrichment in Akkermansia bacteria and bifidobacteria, and a decrease in Prevotella.

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

By the way, along with the high protein diet, there were also:

• a decrease in another bacterium of the genus Prevotella: Prevotella_2. This bacteria is associated with cardiovascular risk. This could explain that a high protein diet is more favorable for the heart,
• an enrichment in Gemella bacteria: 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 that allows them to still have lactase (the enzyme used to digest lactose, the sugar in milk) at age adult. These people have more bifidobacteria in their microbiota. In this experiment, more than 500 people with this allele followed weight loss diets. It turned out that these people lost the most fat on a high protein diet. Bifidobacteria are therefore perhaps a target of high protein diets.

In conclusion, weight loss has an effect on the composition of the gut 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, especially on kidney health, if it is not followed properly. The Atkins diet remains the most studied diet with the strongest level of evidence. But it is also possible to change the composition of the microbiota in order to promote weight loss without going through the protein diet.