Can gut bacteria make you fat?

The pounds seem to fall off for some people on a diet, while others have a much harder time losing weight – with a tsunami of research performed in the multi-billion dollar weight loss industry to provide answers for those who pile on the pounds. To this end, a simple solution to a problem affecting millions of people worldwide may come in the guise of the microfauna currently residing in our guts.

These microorganisms, also known as the gut microbiota, play a vital role in our bodies. Not only is it a significant player in our immune system, but it also regulates our metabolism and helps us absorb nutrients – meaning, in turn, it can influence our weight. However, mapping the myriad of signaling pathways and mechanisms underlying this bacterial phenomenon has proven challenging, with variables such as bacterial growth rates, dietary efficiency, and immunomodulation posited to be involved.

Now, a study from researchers at the University of Washington shows that the presence of certain species of gut microbiota in people dieting directly affected how many pounds they were able to shed. Christian Diener, Ph.D., lead study author, feels this is exciting because it shows that “Your gut microbiome can help or cause resistance to weight loss, and this opens up the possibility to try to alter gut bacteria to impact weight loss.”

Previous research has shown that specific bacteria present in probiotics help lose weight – with the gut microbiota correlated to body mass index (BMI) and metabolic health markers. Additionally, studies in mice have also uncovered a link between the microbiome and weight gain. However, this link is unclear with many other variables suspected to be involved in weight loss and gain, such as genetics, prior health status, age, physical activity, and diet. Ergo many factors can affect a host of gut microbiota species to regulate whether a person is lean or obese. However, the exact functional determinants underlying this phenomenon remain unclear.

The lab attempts to understand the possible interactions between BMI, dietary patterns, metabolic health, and the gut microbiome in their study. And how these factors may be associated with changes in weight and metabolic health following personalized, healthy lifestyle interventions. To achieve this, the researchers looked at 105 overweight people enrolled in a year-long weight loss program. Interestingly, instead of a specific diet or exercise program, this scheme involved a behavioral coaching program integrating advice from a dietician and nurse.

To track the interaction of the gut microbiota with other factors that caused their weight loss, the researchers recorded various markers related to diet and weight. To do this, they recorded participants’ starting body mass index (BMI) and levels of specific markers of metabolism in the blood – such as cholesterol levels. Stool samples were also collected at the beginning and end of the study to determine the microbial levels present in each participant’s gut. Of the original single-arm, 48 volunteers lost more than 1 percent of their body weight per month over a 6 to 12 month period. In contrast, the remaining fifty-seven individuals who did not lose any weight also had a stable body mass index (BMI) over the same period. The researchers analyzed blood metabolites, blood proteins, clinical labs, dietary questionnaires, and gut bacteria once the results highlighted the physical discrepancies between the two groups.

The scientists then compared the data gained from people who had lost weight to those whose weight remained unchanged. They observed that various blood markers related to metabolism were only minimally different between those who did and didn’t lose weight. However, when it came to the species of bacteria contained within the guts of the two groups, there was a noticeable difference. Namely, people who lost more weight had more beneficial bacterial enzymes in the intestine. Gut microbes produce these enzymes to help break down complex carbohydrates, like those found in whole grains, into simple sugars – making them easier to digest and potentially less likely to be stored as fat. The team also found that the growth of bacterial colonies, particularly the bacteria Prevotella, helped produce higher levels of healthy substances like short-chain fatty acids, substances known to reduce inflammation, which may also help to facilitate weight loss.

After allowing for age, sex, and BMI, the researchers identified 31 variables associated with weight loss in the stool. These included polysaccharide and protein degradation genes, stress-response genes, respiration-related genes, cell wall synthesis genes, and gut bacterial replication rates. A notable observation was that the ability of the gut microbiome to break down starches increases in people who did not lose weight as the body could absorb more of these molecules. Another crucial finding saw an increase in the number of genes that help bacteria proliferate and assemble cell walls in people who lost more weight. Together, results suggest that the microbiota may influence host weight loss responses through variable bacterial growth rates, dietary energy harvest efficiency, and immunomodulation.

Looking forward, the researchers state that if these findings are verified, they could be very promising for people looking to lose weight and keep it off. With this in mind, the next step will be investigating methods to modify the gut microbiota to cause the host to lose weight. They theorize that they could do this by administering probiotics and prebiotics or performing more advanced treatments such as fecal microbiota transplantation – a procedure in which stool from a healthy donor is placed in a patient to alter the gut microbiome. “At a minimum, this work may lead to diagnostics for identifying individuals who will respond well to moderate healthy lifestyle changes, and those who may require more drastic measures to achieve weight loss,” said ISB Assistant Professor Dr. Sean Gibbons, corresponding author on the paper. “By understanding which microbes and metabolic processes help promote weight loss in the gut microbiome, we can begin to design targeted prebiotic and probiotic interventions that might push a weight-loss resistant microbiome to look more like a weight-loss permissive microbiome.”

Source: ScienceDaily

Image created by Allison Kudla, PhD / ISB and vrx123 and Atlas / Adobe Stock

Readers can find the study in the opensource journal mSystems.

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