Weight loss: Protein-rich diets may change gut bacteria, reduce fat

This short-term experimental study lasted four weeks and included 16 mice.

For the first two weeks, the mice were fed a regular carbohydrate diet. The researchers then switched the mice to four distinct protein diet groups for the remainder of the study:

• standard protein diet
• 10% aromatic amino acid
• 10% branched-chain amino acid diet
• 5% aromatic amino acid and 5% branched-chain amino acid diet

The volume of each diet was the same and contained an equal amount of protein.

The researchers collected daily fecal samples and took weekly body composition measurements to monitor changes in body fat and muscle mass.

They extracted DNA from the fecal samples and analyzed it to observe how the mice’s gut bacteria changed throughout the study.

The study found that the gut microbiota responded differently to each type of diet, showing significant changes from the carbohydrate diet to the four different protein diets.

Using machine learning, researchers could predict with 97% accuracy which protein diet the mice were consuming just by looking at their gut bacteria.

For MNT, Adejumo elaborated on which protein diets specifically resulted in the greatest fat mass and body weight reductions.

“A combination of 5% branched-chain amino acid with 5% Aromatic amino acids resulted in the lowest body weight, whereas [10% aromatic amino acid diet] had the lowest percentage of fat mass but the highest weight increase,” he said.

“These results imply that beyond the type of diet, the type of gut microbiome that metabolizes the diet is much more important. The gut microbiome metabolism of the diet has the biggest impact on the host body composition.”
— Samson Adejumo, lead researcher

“The result of weight [and] body composition is unexpected because branched-chain amino acids are involved in muscle protein building and we would expect that an increase in [branched-chain amino acid] intake will increase lean mass and not fat mass,” he said.

Further research is needed to confirm if the protein diets caused all the observed changes in body composition and gut bacteria in mice.

However, the predictable patterns identified by the researchers suggest a link between the protein diets and changes in the gut microbiome.

Adejumo explained how the observed changes in gut microbiota may relate to body composition and weight loss.

He said aromatic amino acids, primarily involved as precursors of neurotransmitters, are essential for maintaining the body’s normal biological functions.

“In contrast, branched-chain amino acids are involved in maintaining muscle function and producing proteins in muscle development.”

He further explained:

“Changes in the gut microbiome reflect the bioavailability of the essential ingredients to the gut microbiome. Whenever a gut microbiome can utilize the diet ingredients, it will positively affect the body composition particularly, the fat mass and lean mass.”

In essence, changes in gut microbiota can be influenced by the types and quantities of protein consumed, subsequently affecting body composition. This also implies that a healthy gut microbiome may be crucial for maintaining optimal body composition and weight.

MNT also spoke with Alyssa Simpson, RDN, CGN, CLT, a registered dietitian, certified gastrointestinal nutritionist, and owner of Nutrition Resolution in Phoenix, Arizona, who was not involved in the study.

“Changes in gut microbiota can significantly influence body composition and weight loss by altering how efficiently calories are extracted from food,” she stated.

She suggested, for example, that a higher ratio of certain bacteria may enhance calorie absorption, potentially contributing to weight gain.

Additionally, Simpson noted that “certain bacteria produce lipopolysaccharides that may promote inflammation and fat accumulation, whereas beneficial bacteria may contribute to maintaining gut barrier integrity and regulating appetite through hormone and neurotransmitter production.”

According to Simpson, more research is needed, but diets rich in certain proteins, particularly plant-based proteins, have been shown to improve human gut health and body composition.

“Plant-based protein diets promote gut health by supporting beneficial bacteria and regular bowel movements. They are generally lower in calories and saturated fats compared to animal-based diets, potentially aiding in weight management and reducing body fat.”
— Alyssa Simpson, RDN, CGN, CLT

Plant-based diets are also rich in dietary fibers, promoting the growth of microbial species that ferment fiber into beneficial metabolites like short-chain fatty acids, which are associated with numerous health benefits.

Even though the body produces them, she also suggests getting dietary sources of amino acids like glutamine and arginine, which “contribute to maintaining a robust gut barrier, preventing harmful substances like lipopolysaccharides from entering the bloodstream and potentially influencing body composition.”

For those looking to enhance gut microbiome, overall health, and body composition through diet, Simpson recommends prioritizing “a rich variety of plant-based foods like fruits, vegetables, nuts, seeds, whole grains, and legumes.”

She also advises “moderate protein intake to maintain muscle and metabolic health without excessive unhealthy fats.”

Most importantly, “select a dietary approach that suits your personal preferences, health objectives, and lifestyle for sustainable results,” Simpson emphasized.

Adejumo said, as a next step, “we plan to do some functional analysis and perform some mechanistic experiments to be able to improve overall health.”

“We also intend to formulate our diets with single amino acids to fully understand the effect of individual amino acids on diet and identify specific gut microbial strains involved in protein fermentation,” he added.

While more research is needed and animal studies don’t directly translate to humans, learning how dietary protein fermentation affects gut bacteria could help inform the creation of personalized diets that modify the gut microbiome to promote better health and weight management outcomes.

“This concept of personalized nutrition holds promise for broader integration into healthcare practices, potentially revolutionizing how dietary advice is tailored to optimize health outcomes in diverse populations,” Simpson concluded.