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.

Dongqing Wang, an assistant professor of Global and Community Health at George Mason’s College of Public Health, is pioneering research in prenatal nutritional interventions. His latest report identifies prenatal supplements that reduce health risks to small and vulnerable babies. This research was published in the prestigious The Lancet Global Health journal and funded by the Bill and Melinda Gates Foundation. 

Wang found that compared to folic acid and iron alone, a multiple micronutrient supplement led to a 27% lower risk of giving birth to “small vulnerable newborn types,” or babies who suffered from preterm birth, low birthweight, and small-for-gestational-age birth-the three groups most likely to result in infant death. 

In the past, these birth outcomes were all treated as separate conditions. Wang, however, delves into emerging science to look at different combinations across the three outcomes. Low birthweight, for example, can occur because of a short pregnancy, and growth restrictions can lead to babies born too small for their developmental age. 

Small vulnerable newborn types may have distinct mechanisms, health impacts, and intervention strategies. This work is the first to examine the effects of prenatal multiple micronutrient supplements and small-quantity lipid-based nutrient supplements on the emerging outcomes of small vulnerable newborns.” 

Dongqing Wang, Assistant Professor of Global and Community Health, George Mason’s College of Public Health

Folic acid and iron have been used to support prenatal health since the 1970s. Wang explored the effects of two additional types of prenatal supplements on women in low- and middle-income countries: prenatal multiple micronutrient supplements (MMS), similar to a common multivitamin, and small-quantity lipid-based nutrient supplements (SQ-LNS), which provide caloric nutrition and fatty acids in addition to vitamins. 

He found that nearly all of these vitamins conferred some type of benefit-and some of them were hugely beneficial. 

“This study underscores the important promise of nutritional supplements in prenatal care in low- and middle-income countries,” says Wang. “In particular, the protective effects of prenatal multiple micronutrients on most small vulnerable newborn types, particularly those with the greatest mortality risk, strongly supports switching from iron and folic acid supplements to MMS as the standard care.” 

Combining 16 different studies, Wang analyzed how prenatal nutrition correlates to the occurrence of small vulnerable newborns. He believes that the right prenatal supplements can help mitigate them. Since more than 90% of pregnancies resulting in low birthweight occur in low- and middle-income countries, including those in sub-Saharan Africa and South Asia, Wang focused this work on those regions. 

The Lancet Global Health will publish “The effects of prenatal multiple micronutrient supplements and small-quantity lipid- based nutrient supplements on small vulnerable newborn types in low- and middle- income countries: a meta-analysis of individual participant data” in January 29, 2025. Additional authors include Enju Liu, Nandita Perumal, Uttara Partap, Ilana R. Cliffer, Janaína Calu Costa, Molin Wang, Wafaie W. Fawzi, and more than 40 data contributors from all over the world who provided the individual participant data used in this landmark analysis. 

For centuries, people have extolled the health benefits of green tea, like reducing the risk of cardiovascular disease, maintaining skin health, promoting weight loss, and even lessening the risk of dementia.

Now, recent research from Japan adds to the evidence that it helps fight cognitive decline and thus reduces dementia risk, with the scientists finding that older people who regularly drank green tea had fewer of the brain lesions characteristic of dementia than those who did not drink it.

The study was published in Science of Food.

Steven Allder, MD, a consultant neurologist at Re:Cognition Health, who was not involved in this study, told Medical News Today that while the link between green tea and fewer cerebral lesions “highlights its potential as a preventive strategy against age-related cognitive decline”, the results should be interpreted cautiously, “as confounding variables like lifestyle and dietary habits may contribute to these outcomes”.

Antioxidants

Green tea has one of the highest levels of antioxidants of any tea, as well as polyphenols, which could bring various health benefits, including: helping combat some cancers, including those of the breast, gastrointestinal tract, lung, prostate and liver; encouraging weight loss; anti-inflammatory effects on the skin and cardiovascular system; and cognitive benefits.

The study, led by Kanazawa University Graduate School of Medical Sciences, investigated almost 9 000 adults recruited from the Japan Prospective Studies Collaboration for Ageing and Dementia between 2016 and 2018, to determine whether green tea or coffee had any effect on brain health.

All participants filled in a Food Frequency Questionnaire, with their daily intake of green tea and coffee being classified into four groups: 0-200ml, 201-400ml, 401-600ml, and at least 601ml.

One cup of tea was equivalent to 200ml.

They also underwent magnetic resonance imaging (MRI) scans to assess cerebral white matter lesions, hippocampal volume and total brain volume.

The researchers controlled for sociodemographic factors, such as age, sex and education level, and in a second analysis, adjusted for medical factors, including hypertension, diabetes mellitus, APOE e4 allele (which increases dementia risk), body mass index (BMI), cholesterol levels, smoking and drinking habits, ECG abnormalities, history of stroke, depressive symptoms, cognitive function and regular exercise.

They excluded 1 519 participants who had mild cognitive impairment at baseline. In further analysis, the researchers investigated whether depression or having the APOE e4 allele had any effect on their results.

Fewer lesions

After adjusting for confounding factors, they found a significant association between higher green tea consumption and fewer cerebral white matter lesions.

They did not see any association with coffee consumption. They also found no association with hippocampal or total brain volume.

Allder explained why they might have seen these effects: “This could be due to the neuroprotective properties of catechins like EGCG in green tea, which combat oxidative stress, reduce inflammation and inhibit beta-amyloid aggregation.”

Coffee did not show similar benefits, possibly because green tea’s unique composition, like catechins, might be more effective against white matter lesions than coffee’s compounds, which are mainly chlorogenic acid and caffeine, he added.

The effects of green tea did not, however, extend to participants with the APOE e4 allele, or those with depression.

In these people, the researchers found no association between green tea and fewer brain lesions. They suggest that, as both are strong risk factors for dementia, green tea may not be effective in reducing white matter lesions in these individuals.

Allder agreed. “The absence of benefits in people with depression might be due to the interaction between chronic inflammation and oxidative stress associated with depression, which could counteract the neuroprotective effects of green tea.

“Similarly, the lack of effect in APOE e4 carriers suggests a genetic predisposition that could diminish green tea’s impact, potentially due to APOE e4’s strong association with amyloid pathology and vascular contributions to cognitive impairment.”

Any side effects from green tea?

Unlike black tea, green tea is not fermented, so retains polyphenols, such as flavanols, of which catechins are particularly important. Catechins are antioxidants that neutralise free nitrogen and oxygen radicals, with studies showing they reduce the inflammation that may lead to many chronic and age-associated conditions – like some cancers, cardiovascular diseases and neurodegenerative diseases.

The researchers warn that there were limitations to the study: it was cross-sectional so they cannot determine a causal relationship between green tea consumption and reduced white matter lesions.

Also, they could not account for how the tea was brewed, or whether participants were also consuming it in snacks. And, because there were few black tea drinkers in their Japanese cohort, they could not compare the effects of green and black teas.

Allder called for further studies on diverse populations, different ethnic groups and in different regions, to determine whether genetic and lifestyle factors influence the benefits of green tea.

“Research should also focus on targeted subgroups, like people with depression or the APOE e4 allele, to explore the mechanisms that might limit green tea’s effectiveness in these populations.

Study details

Green tea consumption and cerebral white matter lesions in community-dwelling older adults without dementia

Shutaro Shibata, Moeko Noguchi-Shinohara, Ayano Shima et al.

Published in NPJ Science of Food on 7 January 2025

Abstract

This study investigated the association between green tea or coffee consumption with cerebral white matter lesions and hippocampal and total brain volumes among 8766 community-dwelling participants recruited from the Japan Prospective Studies Collaboration for Ageing and Dementia between 2016 and 2018. A Food Frequency Questionnaire was used to assess green tea and coffee consumption, whereas brain magnetic resonance imaging was performed to assess cerebral white matter lesions, hippocampal volume, and total brain volume. Multivariable-adjusted analysis revealed significant correlations between fewer cerebral white matter lesions and higher green tea consumption, whereas no significant differences were found between green tea consumption and hippocampal or total brain volume. Regarding coffee consumption, no significant differences were observed in cerebral white matter lesions or hippocampal or total brain volumes. Hence, higher green tea consumption was associated with fewer cerebral white matter lesions, suggesting that it may be useful in preventing dementia.

NPJ Science of Food article – Green tea consumption and cerebral white matter lesions in community-dwelling older adults without dementia (Open access)

Medical News Today article – Green tea drinkers have fewer brain lesions linked to dementia (Open access)

See more from MedicalBrief archives:

Green tea extract promotes gut health, lowers blood sugar – Ohio study

Benefits of green tea revealed in new pancreatic cancer study

Additive effects of green tea and coffee on mortality risk in type 2 diabetes patients