• Mayo Clinic Q and A: Probiotics, gut bacteria and weight — is there a connection?

a medical illustration of gut bacteriaDEAR MAYO CLINIC: I’ve read some research that indicates one possible contributing factor to obesity is the balance of bacteria in a person’s gut. In someone who is obese, is it possible to right that balance by taking a probiotic supplement, such as Lactobacillus gasseri, in conjunction with a balanced diet and exercise?

ANSWER: It is true that the gut bacterial population in people who are obese is different from the population in people who are lean. Whether this difference contributed to obesity, however, or is a consequence of obesity is unknown. The research on this subject so far hasn’t yielded clear answers. Although taking a probiotic is unlikely to cause harm, it may not help fight obesity.

First and foremost, it’s important to understand that weight gain is essentially a function of energy imbalance. You gain weight when you take in more calories than your body burns. And there is some evidence that bacteria in the gut play a role in how efficiently the body extracts energy from the food that reaches the small intestine.

Your digestive tract, also called the gut, contains trillions of bacteria. Many of those bacteria play a number of useful roles in the body, including metabolizing nutrients from food. While much of the bacteria in the gut are valuable, some are not. There have been studies done about how an imbalance between good and bad gut bacteria could contribute to certain medical disorders.

Eating foods such as yogurt and sauerkraut that contain probiotics — a type of “good” bacteria — or taking a probiotics supplement have been credited with health benefits. Although more research is needed, there is some evidence that probiotics might improve gut health.

To date, however, the only studies that have shown convincing results that changing the composition of gut bacteria (sometimes called the gut microbiome) affects weight have been performed using germ-free mice. In humans, on the other hand, the data are murky when it comes to the role of probiotics in helping with weight loss.

An analysis of the results of published research studies that have investigated probiotics and weight loss revealed no clear answers. In part, that’s because the research methods varied widely among those studies, and they included a range of different probiotics.

What is clear is that the most important factor determining the makeup of the gut microbiome is diet. But, again, that calls into question which comes first. Does obesity lead to a certain type of microbiome? Or does a certain type of microbiome lead to obesity? At this point, this is unknown.

That said, there are some steps you can take to maintain a healthier gut microbiome overall. For example, eating plenty of fruits and vegetables appears to help good bacteria in your gut thrive. Limiting fat, sugar and animal sources of protein may help, too, because research shows that diets high in those foods are correlated with a more unfavorable bacteria makeup in the gut.

Taking a probiotic supplement also may improve the health of your gut microbiome, but it’s unclear what role those supplements play in weight loss. The most reliable way to lose weight is to eat a healthy diet and exercise regularly, so you’re burning more calories that you’re consuming. If you have questions about the diet and exercise that’s right for you, talk with your health care provider. — Dr. Meera Shah, Endocrinology, Mayo Clinic, Rochester, Minnesota

Related articles