How to Modify Your Gut Bacteria to Lose Weight

February 3, 2022 , ,

Did you know that our microbiome, which is the set of bacteria present in the gastrointestinal tract, can affect our ability to lose weight?

weight loss meal plans

The microbiome includes trillions of bacteria and archaea of more than a thousand different species.  Research indicates that the diversity of these microbes may have a preventive effect on long-term weight gain. The species of bacteria present in the gut microbiome differs from one person to another. For example, most studies have noted that the Firmicutes/Bacteroidetes ratio is significantly higher in obese subjects. In addition, studies have shown correlations between an increased amount of Bacteroidetes in the stool and weight loss, and between Firmicutes and the development of obesity.

Several potential mechanisms of action help explain how the gut microbiome can affect weight management. The gut microbiome plays a role in inflammation and metabolism, among other things, via the production of short-chain fatty acids (SCFAs). Gut dysbiosis, i.e. an alteration in the balance of bacteria in the gut, can promote weight gain. Studies have shown that exposure to antibiotics at two-years of age increases the likelihood of developing obesity later in life, and that alterations in the gut microbiome after antibiotic use can lead to weight gain. Gut dysbiosis, linked to an increase in the Firmicutes species, has been associated with changes in digestive hormones (gastrin, cholecystokinin, somatostatin and ghrelin), which can lead to decreased satiety and increased appetite and caloric intake.

Just recently, researchers at the University of Washington in the United States demonstrated via a clinical study that the composition of the gut microbiome can help predict the potential for weight loss. To understand the effect of gut bacteria on weight loss, the researchers looked at 105 overweight people, all enrolled in a one-year weight loss program. They found that people who had lost weight (at least 1% of their body weight on average each month) had more beneficial bacteria in their gut. While these results will need to be verified with a wider group of subjects, they hold great promise for people looking to lose weight without regaining it because, unlike genes, a person’s gut microbiome can be altered. Ways to alter the microbiota may include dietary changes, taking probiotic and prebiotic supplements, and more advanced treatments like fecal transplantation.

Probiotic supplements and weight loss

A meta-analysis including 12 randomized controlled studies with a total of 821 subjects was conducted to examine the effect of probiotic supplements on body composition in overweight or obese adults. Adults who received probiotics showed significant reductions in body weight, BMI, waist circumference, and fat percentage, when compared to adults in the control group.

A systematic review including 14 clinical studies also showed that probiotic supplements have the potential to help weight loss and fat loss in overweight subjects. The results suggest that the beneficial effects depend on the strain of probiotic chosen. Probiotics that can be useful for weight loss include several species of Lactobacillus such as L. gasseri, L. rhamnosus, L. amylovorus, L. plantarum, L. curvatus, L. acidophilus and L. casei. Beneficial effects on weight and fat mass seem to occur when probiotics are taken for at least 12 weeks. The beneficial effect of these microorganisms could be associated with a modulation of the altered gut microbiome in overweight subjects. Further studies are needed to determine the best strains for weight loss, dose, and duration of treatment to achieve beneficial results.

In Canada, for adults, UltraFlora Control, Genestra Brands HMF Metabolic and FloraVantage Control are among the leading probiotic supplements whose effectiveness for weight loss is supported by at least one good quality controlled clinical study.

Food and the gut microbiome

Westernization of dietary habits has led to microbial dysbiosis. A high-fat and low-fiber diet has been shown to reduce intestinal microbial diversity, protective gut bacteria and SCFA. In contrast, a high-fiber diet that includes a variety of plant-based whole foods (fruits, vegetables, whole grains, nuts, seeds and legumes) increased microbial diversity and was associated with reduced weight gain in humans, independently of energy intake. In this sense, studies suggest that a vegetarian diet as well as the Mediterranean diet promote a balance of bacteria that is favorable for weight loss (an increase in Bacteroidetes and decrease in Firmicutes).

If you want to lose weight, our Mediterranean diet meal plans can help you with their balanced meals, which are rich in plant-based whole foods, that will nourish your gut microbiome.


  • Aoun, Darwish et Hamod (2020) The Influence of the Gut Microbiome on Obesity in Adults and the Role of Probiotics, Prebiotics, and Synbiotics for Weight Loss. Prev Nutr Food Sci; 25(2): 113–123.
  • Diener et coll (2021) Baseline Gut Metagenomic Functional Gene Signature Associated with Variable Weight Loss Responses following a Healthy Lifestyle Intervention in Humans. mSystems 6:e00964-21.
  • Wang et coll. (2019) The Potential Role of Probiotics in Controlling Overweight/Obesity and Associated Metabolic Parameters in Adults: A Systematic Review and Meta-Analysis. Evid Based Complement Alternat Med; 2019: 3862971.
  • Crovesy et coll. (2017) Effect of Lactobacillus on body weight and body fat in overweight subjects: a systematic review of randomized controlled clinical trials. International Journal of Obesity; 41:1607–14.
  • Skokovic-Sunjic (2021) Clinical Guide to Probiotic Products Available in Canada 2021 Edition.


Kathryn Adel
Kathryn completed degrees in kinesiology and nutrition, as well as a Masters in Sports Nutrition. She is a member of OPDQ and of the Academy of Nutrition and Dietetics. She ran track and cross-country at a national level. Kathryn specializes in sports nutrition, weight loss, diabetes, as well as heart and gastrointestinal health. Kathryn is experienced with the low FODMAP diet and she completed the Monash University low FODMAP dietitian's training.

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