Excess body fat has become one of the country’s most prevalent health problems—affecting roughly 2 out of every 3 adults and 1 out of every 3 children in the United States.^1,2 Far from a “cosmetic” problem, being significantly overweight increases the risks of suboptimal health conditions and disorders.^3,4 Additionally, carrying extra weight can affect a person’s energy levels, mobility, and overall quality of life.⁵ For all these reasons, finding effective ways to maintain a healthy body mass index has necessarily become one of this country’s top priorities.  

Although we all know the importance of lifestyle factors such as diet and exercise for maintaining a healthy body weight, you may be surprised to learn that genetics, hormones, and the trillions of microorganisms living in your gut (otherwise known as your gut microbiota) also seem to play significant roles. In this article, we review some of the most compelling evidence supporting a link between healthy gut microbiota and weight management.

Research Supporting a Link Between Gut Health and Weight Management 

In one of the first studies to document a link between gut microbiota and body composition, a group of researchers set out to compare the gut bacteria of obese and lean mice from the same litter. In addition to differences in the types and proportions of bacteria present, these researchers noted important differences in how efficiently the two body types harvested energy (calories) from food.⁶ The researchers also transplanted gut microbes from the obese mice into their leaner counterparts and found that within two weeks of transplantation, the lean mice had increased their fat stores and developed issues regulating blood sugar—despite being fed a reduced-calorie diet.⁶

Together, these findings suggest that the types of bacteria present in an organism’s gut microbiota can affect how efficiently energy from food is stored or expended, and ultimately, the likelihood of weight issues.⁶

Further support for the role of gut bacteria in weight management comes from a different study showing that the relative proportions of two dominant bacterial groups, the Bacteroidetes and the Firmicutes, varied significantly between obese and lean humans.⁷ More specifically, obese individuals were found to have lower proportions of Bacteroidetes than leaner individuals; however, an increase in the proportion of Bacteroidetes to Firmicutes bacteria was observed in obese individuals who made efforts to lose weight. 

These findings suggest that manipulating the composition of the gut—as well as the proportions of gut microbes—may have therapeutic implications for weight management.⁷

Probiotics and Gut Health 

One way to alter the microbial proportions and composition of the gut is by incorporating probiotics and prebiotics into the diet. Probiotics are live microorganisms (bacteria and yeasts) that confer health benefits to the host when taken in sufficient amounts.⁸ Prebiotics, on the other hand, refer to non-digestible carbohydrates that selectively induce the growth or activity of beneficial microorganisms (i.e., probiotics).⁹ Both probiotics and prebiotics can be attained through either food sources or supplements.

Importantly, a growing body of research suggests that supplementing with probiotics and/or prebiotics can help support intestinal health and a healthy body weight.¹⁰

Studies Looking at the Effects of Probiotics on Weight Management 

In one study, researchers investigated the effects of prebiotics and probiotics on intestinal health and weight management by randomly assigning significantly overweight participants to receive either: 1) prebiotic dietary fiber (12g/day), 2) probiotic bacteria (10 billion CFU of a strain of Bifidobacterium animalis), 3) a combination of prebiotic fiber + probiotic bacteria, or 4) a placebo.¹¹ The data indicated that the groups receiving either probiotics or ‘probiotics + prebiotics’ reduced their body fat mass, body weight, waist circumference, and food intake significantly more than individuals receiving the placebo. 

Individuals in these groups also showed positive changes related to gut barrier function and inflammation—two important markers of intestinal health. Notably, the positive changes in body mass index and intestinal health were most pronounced in the group receiving the probiotics and prebiotics, suggesting that the two worked particularly well together.¹¹

In a different study investigating the effects of probiotics on weight loss and maintenance, significantly overweight participants were randomly assigned to take either a probiotic + prebiotic supplement containing 324 million CFU of Lactobacillus rhamnosus with oligofructose and inulin (as a prebiotic), or a placebo for 24 weeks.¹² Participants were also asked to follow an energy-restricted (low-calorie) diet for the first 12 weeks, followed by an unrestricted diet the following 12 weeks. At the end of the first two-week period, women in the probiotic + prebiotic formulation group had lost significantly more weight than women in the placebo group and continued to lose weight during the unrestricted period—despite the relaxation of calorie restrictions. Conversely, women in the placebo group actually gained weight during the unrestricted period.¹²

In addition to weight loss, women receiving the probiotic + prebiotic formulation saw significant changes in their circulating leptin concentrations (a hormone made by fat cells and believed to help inhibit hunger and regulate energy balance). On the whole, the results from this study show that a probiotic formulation containing lactobacillus rhamnosus and prebiotics helped women to achieve satiety and sustainable weight loss.¹²

Are Probiotics Effective for Everyone?

Something to consider when evaluating the research on probiotics and weight management is that the majority of studies to date have been conducted using obese participants, who we understand to have different microbiota than people of average weight.^6,7 However, in recent years, the results from several randomized control trials show similar probiotic benefits for weight management in non-obese individuals, suggesting that people of average or above-average body weight can also benefit from supplementation with probiotics.^13–15

In one such study, participants were randomly assigned to receive 20 billion CFU of a strain of Bifidobacterium breve, or a placebo. Despite both groups having similar body fat mass and body fat percentage at the beginning of the study, the individuals in the probiotics group had significantly lower body fat mass and fat percentage halfway through the intervention, and at the end of the intervention.¹³

Although more research is needed to understand how different probiotic strains and combinations of strains affect the non-obese microbiota, preliminary research suggests that probiotics and prebiotics can help individuals of different body types achieve and maintain a healthy body weight. However, which probiotic strains provide the most definitive benefits towards this end is still under investigation. 

Conclusion

Since discovering a link between gut microbes and body composition fifteen years ago, research investigating the gut microbiota’s influence on metabolic health has greatly advanced our understanding of how probiotics and prebiotics can help support a healthy body weight.^6,7,10 In light of these promising findings, we encourage individuals struggling to maintain a healthy body weight to speak with their health care provider about whether integrating probiotics or prebiotics into their diet could help.