Probiotics and weight loss: the real skinny on whether they work

You’ve probably seen probiotics in food, cosmetics, and even pet food. You may have heard that probiotics live in your gut as part of your digestive system. You may know that they are good for your overall health and wellness. But what about probiotics for weight loss? Do they work for this purpose? 

Let’s examine what the research has to say.

Probiotics are bacteria found in your gut that help you digest your food effectively along with other health benefits. The word itself gives a clue about their helpfulness—pro means for, and biotic means life (Kerry, 2018).  

You have trillions of these microorganisms in a healthy gut with different strains, weights, and mechanisms of action. Researchers have found that both live and dead gut bacteria have jobs to do in the body, though live strains are more effective (Plaza-Diaz, 2019).

One of the most important jobs of your gut flora or intestinal bacteria is to form a barrier against viruses, bacteria, and other infectious organisms, as well as dangerous substances taken into your body. Researchers found that these beneficial bacteria impact your digestive health and the way you process the food you eat. They also found that probiotics affect many aspects of health, including (Kerry, 2018):

• Immune system

• Hormone function

• Cholesterol

• Blood pressure

• Allergies

• Diabetes

• Irritable bowel disease

• Brain and gut communication

• Overall health

The most common natural source of probiotics is fermented foods and beverages. Fermentation is a process food and drinks go through where bacteria and yeast break down components and change the texture, smell, taste, appearance, and structure of the food or drink (Marco, 2017). 

Some well-known fermented food and beverage products include (Marco, 2017):

• Yogurt and Kefir 

• Kimchi

• Miso

• Sauerkraut

• Beer

• Kombucha

Almost all foods can undergo fermentation: fruits, vegetables, dairy and meat products, grains, and honey. It is difficult to measure the exact amount of probiotics in natural food products (Marco, 2017).

You can also buy probiotic supplements. The U.S. Food and Drug Administration (FDA) regulates medications, but most probiotics are marketed as supplements which means they don’t need FDA approval. Probiotic supplements can’t make any health benefit claims about what their product does (for instance: lowering your risk of diabetes or helping you lose body weight) without the permission of the FDA (deSimone, 2019). 

One additional approach is to feed the probiotics you already have. Many of the beneficial bacteria we have in our gut feed on fiber that comes from plants. By incorporating a wide range of fruits, veggies, and other plants into your diet, you can help the naturally occurring probiotics in your gut thrive (Holscher, 2017).

Maintaining a healthy weight is a complex interplay of how much food you eat, what types of food you eat, exercise patterns, and genetics. There’s been a lot of research on how weight gain, a high amount of belly fat, an elevated body mass index (BMI), and obesity impact health, especially with diseases like diabetes, coronary artery disease, and hypertension. 

About 20 years ago, scientists began studying how gut bacteria impact metabolism, insulin resistance, and fat storage in the way they break down, absorb, and store nutrients from food. At the same time, other researchers looked at the link between obesity and the overuse of antibiotics, which kill off good gut bacteria, along with infectious bacteria. They found that a healthy gut balance with more beneficial bacteria and lower rates of bad bacteria affected the health of the body by lowering inflammation, weight gain, and the effects of chronic diseases (Aoun, 2020).

Scientists hypothesize that a better balance of good bacteria (probiotics) in the digestive tract may help the intestines digest, absorb, store and metabolize food more effectively. Some beneficial probiotics work by controlling appetite, while others inhibit fat storage. These improved functions might help with weight management and eventual weight loss (Abenavoli, 2019).

Animal studies of Lactobacillus strains, especially L. Casei strain Shirota (LAB13), L. Gasseri, L. Rhamnosus, L. Plantarum, and Bifidobacterium strains B. Infantis, B. Longum, and B. Breve B3 were successful in lowering weight gain and reducing fat accumulation. Researchers then used these strains in studies on people (Schutz, 2021).

Studies were done on multiple groups of people with and without obesity: children, men, and pregnant, pre-menopausal and post-menopausal women using Lactobacillus gasseri and  Lactobacillus rhamnosus strains. Most showed improvement in their gut microbial composition, inflammatory markers, body weight, and a lowered body mass index (BMI). Other studies used Bifidobacterium with similar results (Schutz, 2021). 

However, in these studies, not all probiotics worked for weight loss and reducing body fat, even if the same strains were used (Abenavoli, 2019).

The bottom line is the scientific jury is still out on taking probiotics to lose weight. There are three main reasons why there’s no definitive answer yet:

1. Most probiotic supplements on the market haven't been well studied and are not regulated by the FDA. This means many commonly sold probiotic supplements may be of questionable quality or not even have any probiotic microorganisms in the bottle at all (Cunningham, 2021).

2. Scientists are still researching how probiotics work, as it is still unclear how gut bacteria contribute to weight gain, body fat, and obesity. There are certain factors that need to be examined, including the probiotic strain, the dose, and how long to take it. Additional factors for consideration include the person's age, baseline body weight, and birth gender (WGO, 2017).

3. While there is some good research on certain probiotic strains, there is a critical need for an increased understanding of the function of other kinds of gut bacteria and the long-term influences of probiotic supplementation on your overall health (Cunningham, 2021).

The World Gastroenterology Organization recommends that you speak to your healthcare professional before taking a probiotic supplement to guide you to a specific probiotic strain, dose, timing, storage of the probiotic, and length of use, whether for weight loss or other health issues (WGO, 2017).

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

April 12, 2021

Written by

Tobi Ash, MBA, RN, BSN

Fact checked by

Steve Silvestro, MD

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About the medical reviewer

Steve Silvestro, MD, Ro

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.