Could weight loss be as simple as taking the right probiotic supplement? Based upon a growing body of evidence, the answer is a definite YES!

The term probiotic is used to describe the beneficial bacteria that inhabit the human intestinal tract. The word is derived from Greek and literally means “for life.” Probiotics include not only the freeze-dried bacteria in capsules available at your health food store, but also fermented foods such as yogurt, sauerkraut, and kefir. Many of these foods rich in probiotics are still of great importance to the diets of most of the people in the world.

A possible link to gut flora and obesity was first discovered by comparing intestinal bacteria in obese and lean individuals and there were significant differences. That led to studies in animals that found that switching the bacterial flora from the colons between fat and skinny mice would reverse their condition. In other words, when skinny mice were inoculated with the bacteria flora of the fat mice, they became fat mice themselves and vice versa.

There are now a few human studies showing that probiotic supplementation can promote weight loss including a recent double-blind, placebo-controlled trial.

Background Data:

The gut bacterial flora is affected by several factors including diet, antibiotic use, other drugs, and various environmental factors. In particular, an altered gut flora (dysbiosis) produced by a diet high in fat or low in fiber has been suggested as one of the causes of the development of obesity and the increased risk of developing insulin resistance. But, the relationship between gut flora and obesity looks like it develops very early in life and that may play a role in setting the stage for a lifelong battle against obesity for many people.

A 2011 study conducted at the Turku University Hospital in Finland provides some additional food for thought. In the study, 159 women were randomized to either Lactobacillus rhamnosus (10 billion colony-forming units) or a placebo for four weeks before expected delivery and six months postpartum. The children were followed over their first ten years. It was found that this short-term probiotic supplementation had a protective effect against excessive weight gain over the first years of life.

As to how does gut bacteria influence weight loss, there are several mechanisms that are now well established. Interestingly, they all impact an enzyme called AMP-activated protein kinase or AMPk for short. The activity of this hormone goes a long way in explaining why some people have no problem maintaining their ideal body weight, while others seemingly fight a major battle to lose weight and keep it off.

Overall, the activity of AMPk plays a major role in determining our body fat composition and especially the amount of visceral “belly” fat that we carry. The most important influencer of AMPk activity ultimately appears to be the sensitivity of the cell to the hormone insulin. Hence, with insulin resistance there is reduced AMPk activity.

Insulin resistance is closely tied to abdominal obesity. As the number and size of fat cells increase, they lead to a reduction in the secretion of compounds that promote insulin action, including a novel protein produced by fat cells known as adiponectin. Making matters even worse is that there is also an increase in the secretion of a substance known as resistin that dampens the effect of insulin.

Adiponectin increases the activation of AMPk, while resistin impairs AMPk activity. So, while adiponectin is associated with improved insulin sensitivity and metabolism, resistin is associated with poor blood sugar control, increased blood lipids, and the development of atherosclerosis. All of these effects are due to the influence these compounds have on AMPk activity. Probiotics appear to help prevent and fight insulin resistance by increasing adiponectin levels and lowering resistin levels which in turn lead to AMPk activation.

New Data:

In a double-blind study conducted in Montreal, Canada, 125 overweight men and women underwent a 12-week weight-loss diet, followed by a 12-week period aimed at maintaining body weight. Throughout the entire study, half the participants took 2 capsules daily providing 3.2 billion colony-forming units of Lactobacillus rhamnosus, while the other half took a placebo.

After the 12-week diet period, the women in the study had an average weight loss of 4.4 kg if they were in the probiotic group and 2.6 kg if in the placebo group. After the 12-week maintenance period, the weight of the women in the placebo group had remained stable but the probiotic group had continued to lose weight, for a total of 5.2 kg per person. So, the math becomes really simple. The women consuming the probiotic supplement lost twice as much weight over the 24-week period of the study. Interestingly, no differences in weight loss were observed among the men in the two groups.


Obviously, there are a lot of questions that need to be answered about probiotics as a weight loss aid. In regards to the study reviewed above, why didn’t the probiotic supplement have any effect in the men? My guess is that it had something to do with the type of bacteria used – L. rhamnosus. There are other species of probiotics in addition to L. rhamnosus that are associated with positive effects on weight loss.

My takeaway message from the above study is that the best weight loss probiotic based upon what we know today would be formula that contains multiple strains. That might increase the likelihood of success. However, it is important to note that just because one strain of bacteria in a given species has a proven action does not mean that another strain will as well, even if they are closely related. Actions and qualities are fundamentally strain specific. So, it just makes sense to take a multiple strain formula at this time. The recommended dosage would be of 10-12 billion CFUs daily.

It is also very important when selecting a probiotic supplement to choose a respected brand. Numerous analyses of commercially available probiotic supplements indicate there is a tremendous range of quality. So, choose wisely.


Sanchez M, Darimont C, Drapeau V, et al. Effect of Lactobacillus rhamnosus CGMCC1.3724 supplementation on weight loss and maintenance in obese men and women. Br J Nutr. 2014 Apr 28;111(8):1507-19.

Dr. Michael Murray

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