Some Lactobacillus Probiotic Strains Are Linked to Weight Gain, Some to Weight Loss


Probiotics are microbes (usually bacteria; sometimes fungi) that give the host some physiological benefits. This can include promoting a healthy weight, whatever that weight might be — could be a gain or loss, depending on what’s the “healthy weight” for a person. 

Lactobacillus species are probiotics. They are found in small amounts in fermented milk products (e.g., cheese and yogurt) and in large amounts in probiotic supplements (i.e., powdered/capsuled). 

“Compounds with antibiotic activity and bacteria with probiotic activity have been widely tested as growth promoters,” says Didier Raoult, MD, PhD, who specializes in infectious disease research in Nature. “The probiotics used in agricultural industries are mainly Lactobacillus.”

Weight Gain Doesn't Mean Fat Gain

Dr. Raoult was later criticized for his misleading viewpoint that indirectly links Lactobacillus to obesity or unhealthy weight. 

“In the livestock industry, probiotics are used to promote growth and lean mass, not adiposity,” argues Gregor Reid, a distinguished professor of microbiology, immunology and surgery at Western University, and the endowed chair in Human Microbiome and Probiotics at the Lawson Health Research Institute. 

“These observations are consistent with weight gain resulting from improved gut function and resistance to infection rather than from a metabolic imbalance that causes obesity,” the professor adds.

First Evidence of Lacto-Obesity Link

A few years after Professor Reid’s critique, Dr. Raoult led a study — that was published in Nature International Journal of Obesity (2011) — detailing the first linkage between certain Lactobacillus species and obesity in humans.

Dr. Raoult and his team quantified the abundance of a few gut microbes in obese and lean individuals. They revealed Methanobrevibacter smithii, Bifidobacterium animals, Lactobacillus paracasei, and Lactobacillus plantarum as markers of healthy weight, whereas Lactobacillus reuteri as a marker of obesity.

Still, associations are mere associations. They don’t indicate the direction of causality. It could be that obese individuals’ gut microbiota are more permissive to L. reuteri colonization, or their diet favors the growth of L. reuteri, or they acquired a taste preference for dairy products containing L. reuteri.

Some Lactobacillus Are Just Different

To look at causation, a randomized controlled trial (RCT) is best. Dr. Raoult thus led another team in 2012 to conduct a meta-analysis that screens all relevant studies in academic databases and harmonizes their data to draw a consensus. They identified 17 human RCTs and 51 studies on farm animals. The results were as follows,

1. Lactobacillus acidophilus administration resulted in significant weight gain in humans and in animals.
2. Lactobacillus fermentum and Lactobacillus ingluviei were associated with weight gain in animals.
3. Lactobacillus gasseri was associated with weight loss both in obese humans and in animals.
4. Lactobacillus plantarum was associated with weight loss in animals.

This meta-analysis shows the effects of Lactobacillus on weight change depending on the species (or strains/types of Lactobacillus). “Attention should be drawn to the potential effects of commonly marketed Lactobacillus-containing probiotics on weight gain,” Dr. Raoult et al. concluded.

On a closer look at their data, however, only two RCTs — one in infants and one in lean adults — showed that L. acidophilus resulted in weight gain. The weight gain was also minor and remained within the normal range. 

A further 2017 meta-analysis update from a different team on the same Lactobacillus research topic found that 9 RCTs reported minor weight and fat loss at <1kg — of which 3 RCTs were with L. gasseri-fermented milk. Other weight loss-associated Lactobacillus species include L. fermentum, L. plantarum, L. rhamnosus, and L. amylovorus.

But there are 2 RCTs — different from the 2012 meta-analysis ones — that reported minor weight gain at <1kg in overweight-to-obese adults. Again, weight and fat gain were minor at. One RCT was with L. acidophilus yoghurt, and the other with L. reuteri capsule. 

As mentioned above, L. reuteri is the one gut bacterium that was found in higher levels in obese than lean adults.

One key limitation the authors admit is that “most studies did not evaluate the food intake of the participants, which can be a bias, especially in those studies in which the Lactobacillus vehicle had caloric content (yoghurt and fermented milk).”

Statistical vs. Real-Life Significance

The 2011 association study and both the 2012 and 2017 meta-analyses yield consistent results. It appears that L. acidophilus and L. reuteri are linked to weight gain whereas L. gasseri is to weight loss in humans.

But all weight gain or loss by Lactobacillus was only <1kg difference. Despite that results are statistically significant, their “effect size” or real-life applications or significance is close to nil. 

This makes it clear that probiotics are meant for a healthy gut, not necessarily for weight control. And perhaps you should check what strains of Lactobacillus are in your probiotic supplements. 

Comments / 3

Published by

MSc Biology | 9x first-author academic papers | 280+ articles on coronavirus | Independent science writer


More from Shin

Comments / 0