Probiotics for weight loss: What is the evidence?

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Probiotics are amongst the most popular nutrition supplements on the market. They have links to an array of health benefits, including improved gut health and enhanced immune function.
nutrition
health benefits
Some research also suggests that probiotics may affect weight loss.
However, there are safety concerns related to the widespread use of probiotic supplements as well.
This Special Feature discusses recent scientific findings related to probiotics and body weight.
body weight
What are probiotics?
The journal Frontiers in Microbiology cites the definition of probiotics as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.”
Frontiers in Microbiology
Certain foods naturally contain probiotics, while some manufacturers add concentrated doses to other foods. However, this article focuses only on probiotic supplements.
Probiotic supplements contain large doses of live bacteria, typically Lactobacilli and Bifidobacteria, that may contribute to improving the composition of colonic gut bacteria and promote health.
Probiotic supplements
Research into the health effects of probiotics has grown tremendously over the past 20 years, as have sales of probiotic supplements.
Some estimates predict that probiotic sales will exceed $64 billion by 2023. This is because of the many links between probiotics and various health benefits.
Some estimates
Even though scientists are still investigating how probiotics work in the body, research has shown that they play a role in enhancing immune function, decreasing inflammation, and positively impacting nervous system function.
investigating
inflammation
Additionally, a 2020 article suggests that probiotics might be a potential treatment for overweight and obesity.
2020 article
obesity
Article highlights:
Gut microbiome and body weight
Researchers have identified a relationship between the gut microbiome — a term that refers to the gut’s entire habitat, including microorganisms, such as bacteria, their genomes (genes), and their surrounding environment — and body weight.
microbiome
Over 1,000 types of bacteria, including Bacteroidetes, Firmicutes, Actinobacteria, Fusobacteria, Verrucomicrobia, Proteobacteria, and Cyanobacteria, populate the intestines.
bacteria
These bacteria perform functions that impact overall health. Disruption to bacterial composition can result in adverse health outcomes, including disease.
For example, researchers postulate that changes to gut bacteria composition may contribute to overweight and obesity in several ways, including increasing insulin resistance, inflammation, and fat storage.
researchers
insulin resistance
It is important to note that research in this area is ongoing, and scientists are still unclear about how altered gut bacteria contribute to obesity.
However, studies have shown that people with overweight and obesity have different gut bacteria composition than people who are not overweight.
Some studies have shown that people with obesity have a higher ratio of Firmicutes to Bacteroidetes bacteria in their gut.
studies
According to two articles, alterations in gut bacteria caused by antibiotic use also have links to weight gain.
antibiotic
weight gain
Are probiotics useful for weight loss? 
Although research is ongoing, studies have shown that probiotic supplementation may promote weight loss and prevent weight gain in humans.
A 2018 systematic review and meta-analysis that included twelve randomized controlled trials (RCTs) and 821 participants found that those who received probiotic supplementation had more significant reductions in body weight, waist circumference, body fat, and BMI than control groups.
2018 systematic review and meta-analysis
BMI
Participants who received higher doses of probiotics and those who received a single strain rather than multiple strain probiotics saw greater body fat loss.
A 2019 systematic review and meta-analysis that included 105 articles and 6,826 participants also found that probiotic treatment led to reductions in body fat, waist circumference, and BMI.
2019 systematic review and meta-analysis
The review found that most of these improvements resulted from treatments containing bifidobacteria (B. breve, B. longum), Streptococcus salivarius subsp. thermophilus and lactobacilli (L. acidophilus, L. casei, and L. delbrueckii).
Additionally, some research suggests that probiotics may help protect against weight gain.
A small 2015 study that included 20 men without obesity found that the men who supplemented with the multi-strain probiotic VSL#3 gained less weight (3.12 vs. 5.06 lbs) and body fat (1.39 vs. 2.83 lbs) when following a hypercaloric, high-fat diet for 4 weeks compared to men who took a placebo.
2015 study
placebo
Researchers think that probiotics may promote weight loss by:
Researchers
increasing the amount of short-chain fatty acid (SCFA) producing bacteria, which increase fatty acid oxidation and decrease fat storage
short-chain fatty acid (SCFA)
decreasing inflammation by reducing the abundance of lipopolysaccharide (LPS) producers
influencing appetite and metabolism
reducing fat accumulation
regulating pro-inflammatory genes
improving insulin sensitivity
Nevertheless, it is important to keep in mind that research investigating the potential effects of probiotics on weight loss is ongoing. Although scientists have narrowed down several ways in which probiotics influence weight, they still do not know the exact mechanisms.
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Are there risks to taking probiotics?
Some scientists have raised concerns over the widespread use of probiotic supplements and warn that they know little about the long-term safety of probiotic supplements.
raised concerns
Researchers have suggested that because probiotics supplements often contain high amounts of probiotics of the same species, taking supplements may lead to the transfer of resistant genes to infectious pathogens.
Researchers
infectious pathogens
This may lead to antibiotic resistance and other adverse health consequences.
antibiotic resistance
Scientists have also warned that there are few reports about probiotic safety and that probiotic studies are often underpowered, poorly designed, and funded by probiotic companies, which may skew results.
Probiotic use may also lead to bacterial overgrowth in the intestine, an increased risk of opportunistic infections, and may cause life-threatening infections in people with weakened immune systems.
overgrowth
It is essential to understand that, although probiotic supplements are widely used and prescribed by healthcare providers, scientists have not determined that probiotics are universally safe or effective.
not determined
Some experts argue that probiotics should be regulated and marketed as drugs rather than dietary supplements to protect consumers.
experts
For this reason, people, especially those who are immunocompromised, should not take probiotics unless instructed by a qualified healthcare provider.
The bottom line
Research suggests that the microbiome influences body weight, and some studies have linked probiotic supplementation to decreased body fat, waist circumference, and BMI.
However, even though probiotics are widely used and prescribed by healthcare providers, there are questions regarding their safety. Researchers do not fully understand how probiotics may negatively and positively impact health.