Probiotics may impact weight and metabolism, but experts are still working to understand the link. Probiotics are friendly microbes that are normally part of the gut microbiome (the community of microbes that live in the intestines). A healthy gut microbiome is important for overall health.

Some initial research shows that certain probiotic strains may support metabolism and promote weight loss by stabilizing insulin levels, reducing inflammation, and controlling appetite.

How Probiotics Affect Body Weight

Taking probiotics can temporarily change the makeup of the microbiome. The strain and dosage of the probiotic may influence the effects. Various strains of probiotics are available as supplements. Not all have been studied for their impact on body weight. Those that have been studied show variable results.

Probiotics may help manage weight by improving the gut microbiome and metabolism in various ways, including:

• Helping stabilize levels of insulin (a hormone that regulates blood glucose levels, enables cells to take in glucose, and promotes storing excess sugars and fats, which can lead to weight gain)
• Stopping the accumulation of fat
• Helping reduce inflammation and insulin resistance (cells do not respond to insulin to take in glucose, resulting in higher blood sugar levels)
• Helping break down fiber and regulating the production of amino acids (building blocks of proteins) in the nervous and digestive systems
• Affecting appetite (a balanced microbiome may influence a series of events in the digestive system that could lead to feeling “full” or reducing appetite)

How Gut Bacteria Affect Metabolism

Metabolism is the process by which the body uses energy to perform body functions. It is an ongoing process that ensures all body systems work, even during sleep. How it works and uses energy (burns calories) changes over time and as a person ages.

Research shows that the makeup of the bacteria in the digestive system affects metabolism. It is still being debated and studied how this happens and which strains of bacteria have what effect. However, the microbiome does influence the metabolic process through cholesterol absorption, blood pressure, and glucose metabolism (how glucose is used and stored).

What Studies Show on Weight Loss and Belly Fat

Much of the research on probiotics and weight has been done on animals. The lack of studies on humans means there isn’t enough information to form recommendations on probiotic supplementation.

One review paper examined six studies on probiotics and overweight or obesity. The studies didn’t all reach the same conclusions about how probiotics affect weight.

In 67% of the studies, participants who took probiotics had lower body weight and body mass index (BMI). In 80% of the studies, people who took probiotics had a reduction in waist circumference.

A few human studies of the probiotic bacterium Lactobacillus gasseri have been reported. In one study, participants who took a supplement of L. gasseri SBT2055 had a decrease in abdominal fat and body weight. Another study showed no change in people who took L. gasseri BNR17.

A study on heat-killed Lactobacillus plantarum LP28 showed that participants lowered their BMI, body fat, and waist circumference. Another study using L. plantarum TENSIA lowered body weight, BMI, and fat mass.

An additional study on Lactobacillus casei strain Shirota (LcS) showed that people taking the probiotic dropped body weight and increased their levels of high-density lipoprotein (HDL) cholesterol (the “good cholesterol”).

Some Probiotics May Also Prevent Weight Gain

Some studies on probiotics also focus on preventing weight gain. Human research is lacking in this area. Much of the research has observed rats and mice. Initial studies on humans have been conducted, but the research results conflict.

If probiotics do help prevent weight gain, one reason might be that they help diversify the gut microbiome.

One review, which included six research papers, examined the use of probiotics to prevent weight gain. It found that products containing multiple strains of Bifidobacterium and Lactobacillus were more likely to show results than other products. 

Probiotic Strains to Try

Research is lacking in determining which probiotics help reduce weight or prevent weight gain. Many of the studies are small in size. It’s not yet known which probiotic will work for which person for the intended effect. Therefore, adding probiotics to the diet might include some trial and error.

At least one research study has shown that the following probiotic bacteria strains help reduce body weight. Most research has focused on strains of Lactobacillus. A few studies have also included Bifidobacterium bacteria. Studied strains include:

• L. gasseri SBT2055
• L. casei strain Shirota
• L. plantarum LP28
• L. plantarum TENSIA
• L. sakei (CJLS03)
• A combination of L. curvatus HY7601 and L. plantarum KY1032
• A combination of L. acidophilus, Bifidobacterium bifidum, B animalis subsp. lactis and L. plantarum)

Potential Risks

It’s important to know that while probiotics are considered safe for most people, they are not without risks.

Some possible risks thought to be of low probability are:

• Systemic infections (the probiotic bacteria invade body tissues or the bloodstream)
• Changing metabolism in an unhelpful or unhealthy way
• Transmission of genes for antibiotic resistance from the probiotic organisms to other organisms in the microbiome
• Overstimulating the immune system

Other risks include:

• Probiotic products not containing what is listed on the packaging
• Interactions with prescription drugs or other supplements
• Gastrointestinal (GI) symptoms

In addition, a few risks are not included in formal studies, but they can occur with any treatment that lacks scientific evidence. The first is financial. Some probiotics can be expensive; taking them for months without results can be considered a waste of money.

Another potential risk is delaying care from a healthcare provider by taking probiotics instead of seeking care. A healthcare provider can provide treatments for obesity, such as exercise, medication, and surgery.

The Best Probiotic Foods for Weight Loss

Eating foods that contain probiotics can be a way to get beneficial gut bacteria. However, solid evidence of how the probiotics in these foods may directly affect weight loss is lacking. But you may reap other benefits. For instance, yogurt that contains probiotics can help lower blood pressure and the risk of heart disease in some people.

Adding probiotic-rich foods to your diet may be an easier and/or less costly way than supplements to work towards a more diverse microbiome. These foods include:

Summary

Weight loss and its connection to the digestive system’s microbiome are complicated and an area of active study. Many unknowns still exist about how the makeup of the gut microbiome affects weight and general health. It is also unknown how individuals might respond to a probiotic supplement.

Probiotic supplements are generally considered safe, but potential risks should be considered. Probiotic foods may also help promote overall health and could be a good choice for those looking to support their microbiome.