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  • Dr. Sarah Penney, ND

What do gut bugs have to do with weight?

Updated: Feb 10, 2020

The age old race to find a magic tool that will slash body weight is still raging on. The weight loss industry flip-flops regularly between touting herbs, different diets and exercise regimes as the next best thing – with some claims backed by research and some lacking any evidence at all. One area of science that has flourished in the last decade to include evidence about weight loss is the study of our gut bacteria and how it influences our health. We have billions of bacteria in our gut – impressive in both amount and diversity. They may play a role in proper immune function, hormone production in the body, mental emotional health, and even health outcomes like autoimmune diseases. And now, research is focusing how these guests in our gut can play a role in our body’s weight management.


Our gut is populated with bacteria as soon as we are born – and goes on to develop into a unique balance of ‘good’ bacteria, ‘ bad’ bacteria and ‘neutral’ bacteria. Often digestive concerns or other health issues are thought to arise after antibiotic use or a viral gut infection that kills off our ‘good’ bacteria and allows our ‘bad’ bacteria to overgrow. The balance of gut bacteria and presence of bacterial strains are different between each person, and early research looking into gut bacteria and obesity found marked differences in these bacterial populations between normal weight and overweight individuals. Individuals who are overweight tend to have a shift towards a specific bacterial balance, and less variety in their gut bacteria. This balance may predispose to more efficient energy and calorie absorption from the diet, predisposing to obesity (1). Animal studies suggest that modifying gut bacteria in mice can promote either weight gain or weight loss, making this an interesting target to treat human obesity.


Probiotics are bacterial strains that can have beneficial effects on the body, and oral administration is thought to influence the bacterial balance in our gut in different ways. These strains can either be consumed in different foods (yoghurt, sauerkraut, fermented soy like tempeh) or taken in supplement form. Supplements allow us to study the effect of a high dosage (higher than you might find in foods) of specific strains on health. Interestingly, certain probiotic strains seem to be useful for certain conditions – one might be helpful to treat IBS, while another may be beneficial for anxiety. Research is ongoing into what strains may assist in weight management, and the results so far suggest it is a treatment worth looking into.


An analysis published in 2018 looked at 15 different clinical trials including 957 overweight participants, aged 18 – 75 years, using a variety of bacterial probiotic supplements in food and capsule form for weight loss. The participants consumed the probiotics anywhere from 3 to 12 weeks. This review concluded that throughout the studies, there was a significant decrease in body weight and fat percentage in the participants consuming probiotics compared to participants in these studies who did not receive probiotic treatment. (2) Another study published in 2016 looked at the effect of treatment using a specific strain of probiotic called Bifidobacterium animalis for the treatment of obesity. Two hundred and twenty five overweight volunteers were randomized to receive treatment with the probiotic alone, the probiotic and a fiber supplement, the fiber supplement alone or no treatment (placebo). Researchers found that after 6 months, abdominal fat loss was much more pronounced in the treatment group that received probiotic alone or probiotic and fiber compared to no treatment. They also found that caloric intake in the probiotic groups seemed to decrease by about 300 calories per day. Inflammatory markers were also measured and showed a decrease in the probiotic treatment groups. (3)

Although the mechanism of exactly how probiotics may effect weight management is still unclear, this early research seems to suggest that targeting the balance of gut flora may be a promising approach for these issues. As a Naturopathic Doctor, I approach weight management as a multi-factorial issue and would consider gut flora balance along-side nutritional counselling, food sensitivity detection, stress management, sleep management, exercise patterns and other lifestyle factors. The improvement of health concerns including weight loss rarely result from simply taking a supplement, but rather a multi-systemic treatment approach that gives more effective results.

Dr. Sarah Penney, ND, MSc





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