The functional medicine community is looking at this question as the nation navigates an obesity epidemic.

Do probiotics help you lose weight? Could shedding pounds be as easy as popping a pill to improve your microbiome?

More than two out of three adults in America were considered overweight or obese based on recent research data from the National Institute of Diabetes and Digestive and Kidney Disorders. Worldwide, 2016 data showed that about 39 percent of the adult population falls into the overweight category and 13 percent are obese.

In response to this health crisis, plenty of research is underway on all the different factors that might be leading to weight gain and weight retention. Some researchers are looking at probiotics and their role in gut health and weight as one possible solution.

Unfortunately, there isn’t one simple solution to battling obesity. Promising research, however, points to the impact of your gut microbiome, or the beneficial bacteria and other microorganisms living in your colon (as well as other areas in your GI tract). This might just mean that probiotics — especially in the right strain(s) for you — may be something to consider for weight loss and maintaining a healthy metabolism.

These little bugs and their byproducts have a significant impact on your overall health, including your level of inflammation, appetite, and metabolism, all of which link probiotics to weight loss. Your gut microflora also plays a role in your risk of developing obesity and associated chronic health conditions such as heart disease and diabetes.

What Is The Microbiome?

Before we get too far into exploring whether probiotics help you lose weight, let’s take a moment to ensure we are on the same page. Here are some of the key players:

  • Probiotics: although sometimes used interchangeably with microbiome, probiotics are live microorganisms that cultivate a healthy microbiome or confer the healthy byproducts of the beneficial bacteria, such as in the form of fermented foods like yogurt or supplements. There are not only numerous species of bacteria, viruses, fungi, and other microorganisms living in your gut, but there are also specific strains of each of these. Each strain has its own impact, and only a small fraction have even been studied for its efficacy, often in terms of a single result.
  • Fecal microbiome transplantation (FMT) also known as gut microbiome transplantation (GMT) — in this process, a healthy donor’s fecal matter and microbiome is administered into the GI tract of the recipient with the purpose to create a healthier microbiota. It has been successful for treating C. diff infections and current research is looking into its efficacy for other diseases, including inflammatory bowel diseases such as Crohn’s and ulcerative colitis.
  • Microbiota – bacteria and other microorganisms, such as viruses and fungi.
  • Microbiome – the microbiota and other genes that live inside the microbial cells.
  • Commensal bacteria – the more formal name for beneficial or good bacteria.

Bacteria live in many different places in your gastrointestinal (GI) tract, including your mouth, esophagus, small intestine, large intestine (also known as the colon), and even your stomach. However, the numbers of bacteria are much, much more significant in the colon, and the byproducts of these bacteria play a much bigger role in health than in the other areas of your GI tract. These byproducts include:

  • Short-chain fatty acids (butyrate, acetate, propionate)
  • Vitamins (K and B vitamins)
  • Bile acids
  • Neurotransmitter production and/or modulation (dopamine, norepinephrine, serotonin, GABA)

In addition to these products, your gut bacteria also play a significant role in your immune health — in fact about 70 percent of your immune system is found in your gut!

When you have an imbalance in bacteria between the good or commensal bacteria and pathogenic bacteria, then you experience something known as dysbiosis. This is where the negative impacts on your health arise. You generally always will have some number of potentially pathogenic bacteria in your microbiome, but when they start to outnumber the good ones, then problems arise.

Taking probiotics can help mitigate some problems by bringing the gut microbiome back to a healthier balance. However, not all probiotics are alike. As discussed above, there are numerous strains of good and bad bacteria and other microorganisms, each of which has its own unique impact on the environment in your gut. Some strains of the same species have completely different effects. Individuals may also have different experiences with the same strain or species. For example, some species and strains have been linked to creating histamines (namely Lactobacillus casei, Lactobacillus reuteri, and Lactobacillus bulgaricus), which may be an issue for those who are histamine sensitive or intolerant, according to Dave Asprey.

Some strains found in studies to mitigate weight gain include:

  • VSL#3 [a probiotic containing a mixture of Bifidobacterium breve (DSM 24732), Bifidobacterium infantis (DSM 24737), Bifidobacterium longum (DSM 24736), Lactobacillus acidophilus (DSM 24735), Lactobacillus delbrueckii subsp. bulgaricus (DSM 247634), Lactobacillus paracasei (DSM 24733), Lactobacillus plantarum (DSM 24730), Streptococcus thermophilus (DSM 24731)]
  • Bifidobacterium lactis B420 — found in Metagenics Ultra Floral Control and Xymogen ProbioMax Lean DF
  • Lactobacillus casei Shirota — found in Yakult

You actually have a microbiome and healthy bacteria residing in many places in your body other than your gut, including on your skin. However, the most talked-about is the gut bacteria because of its significant impact on your total body health (also known as systemic health) and the way in which diet and lifestyle impact your gut. In this article, when the microbiome is referenced, it is regarding the one in the gut, namely the beneficial bacteria in your colon.

We have a vital symbiotic relationship with our bacteria, so it’s good to know how to maintain the commensal bacteria and reduce your numbers of potentially pathogenic bacteria in all your little communities on and in your body, but especially those in your gut.

Can Gut Bacteria Cause Inflammation? And How Does That Relate to Obesity?

Chronic, low-grade inflammation has been implicated in the development of obesity and other metabolic disorders such as diabetes and metabolic syndrome. This inflammation may have many causes, one of which may be dysbiosis in your gut microbiome. The culprit? LPS, or lipopolysaccharides, also known as endotoxins. This creates something known as metabolic endotoxemia, according to a paper in Current Opinion in Lipidology.

Gram-negative bacteria (a classification of bacteria that include many of the infection-causing strains) contain LPS in the outer membrane of their cell. In small numbers, it may not cause a problem, and in most gut microbiomes, you may have up to 70 percent of gram-negative bacteria living there. However, when your balance of beneficial bacteria and potentially pathogenic bacteria become imbalanced, your level of LPS goes up. Additionally, when the LPS enters the bloodstream, it causes problems: they initiate a signal cascade that ultimately leads to pro-inflammatory pathways being turned on until you enter a low-grade, systemic inflammatory state, according to an article published in Biochimie. In fact, metabolic endotoxemia is like a smaller version of sepsis, as it is the same endotoxins that cause the problems, only in fewer numbers than in sepsis.

The secondary component for inflammation? A leaky gut, also known as intestinal permeability. When the tight junctions of your gut (the barrier of your intestinal cells that regulate what enters the bloodstream) start to break down, more levels of LPS can break through into your bloodstream, moving into systemic rotation and wreaking havoc. This leads to increased inflammation levels, which have in turn been linked to obesity and associated metabolic diseases such as diabetes, fatty liver disease, and cardiovascular disease.

Although there are several studies pointing to a link between systemic low-grade inflammation, such as that associated with metabolic endotoxemia, and obesity, the exact mechanisms remain unknown. The inflammation is likely due to disruption in the complex signal network that works between body systems. Thus, one reason that probiotics help with weight loss is that they may be helping to ease the inflammation caused by metabolic endotoxemia.

Does Your Microbiome Control Your Appetite?

Your microbiome may also play a role in appetite; thus, taking probiotics for weight loss may just help you control your food intake. There are many factors involved in appetite control, but two of the main hormones are leptin and ghrelin. Ghrelin is the hormone that the stomach produces to make you hungry, and it also plays a role in your energy homeostasis and metabolism. Ideally, you will have higher levels of ghrelin between meals and during periods of fasting, and it will start to decrease once you begin eating. Long-term fasting impacts your gut hormones in a different way, which is outside the scope of this blog.

Leptin, a hormone found in adipose (fatty) tissue, is supposed to help maintain regulation of energy by telling the body when it needs more energy based on levels of fat deposits, although, in people who are overweight and obese, leptin resistance is common.

Leptin works as an appetite suppressant, so when an individual experiences leptin resistance, then it will not work as well to reduce appetite. In mice, when there is a mutation in the gene for leptin, it leads to obesity, although this mutation is uncommon in humans. However, it does demonstrate that there may be more to uncover the relationship between leptin and obesity.

Other hormones involved in appetite include Peptide YY, CCK and GLP-1 (glucagon-like peptide 1), although there are more. GLP-1 and Peptide YY are also appetite suppressants, and SCFAs also factor into the release of these hormones, according to a paper in Obesity Reviews.

So, how does this relate to your microbiome? For one, one of the short-chain fatty acids (SCFA produced by commensal bacteria, propionate, activates the receptors that stimulate leptin production, which in turn would reduce appetite.

Furthermore, propionate may stimulate the release of the anorectic (or appetite suppressing) hormones GLP-1 and PYY. The researchers also postulate that acetate, another SCFA, may also cross the blood-brain barrier and act as an appetite suppressant signal on its own. To reach effectiveness (increase SCFA production and impact appetite), it required an acute dose of at least 35 grams per day of inulin, one prebiotic, or 15-39 grams per day for two to twelve weeks of oligofructose, another type of prebiotic, based on the findings of the study. For comparison, the recommended dosage for most prebiotics starts at about 10 grams per day, although it can go up to the 30 or 40-gram range depending on the circumstance. Another study referenced in the review also demonstrated that it took nine to 12 months of consuming high-wheat fiber before there was an increase in SCFA and GLP-1 secretion. Thus, taking prebiotics is not a simple, one-time fix but instead requires time to impact the microbiota, their byproducts, and the gut hormones.

One mechanistic study using mouse models demonstrated that an injection of acetate led to an acute reduction on appetite and subsequent food intake that was not related to PYY and GLP-1, demonstrating that acetate may work by affecting the hypothalamus directly.

In one pilot study, levels of CCK and GLP-1 were significantly increased in mice that consumed chicory root. Chicory root is a prebiotic known to fuel some strains of commensal bacteria.

What about affecting appetites in people? There have been some human studies demonstrating the impact of the gut microbiome and SCFAs on appetite. In one randomized, controlled pilot study, participants who were considered obese (based on their body mass index) were given either 4 grams of inulin from a blueberry extract with 2.5 grams of oat beta-glucan (prebiotics) or a placebo twice daily with water. Those who took the prebiotics reported a significantly lower desire to eat and prospective intake of food compared to the control group. There was also an increase in their SCFA levels, although it was not statistically significant. The prebiotic group showed an increase in PYY and a decrease in ghrelin levels, while the placebo group experienced a decrease in PYY levels and although they still had a decrease in ghrelin levels, it was to a lesser degree.

These studies looked more at prebiotics rather than probiotics and weight loss, but they do point to the importance of the microbiome and its byproducts to your appetite and potentially your weight through food consumption.

Bringing it All Together: What Is the Connection Between Your Microbiome And Weight?

There are also studies demonstrating a more direct link between the microbiome make up and excess weight. In one study on children in China, there was a significant difference in the microbiome of the children who were obese compared to their lean counterparts. As the obese children began to lose weight, the microbiome began to have more of the commensal bacteria, namely Bifidobacterium and Lactobacillus, according to Biomed Research International.

In a mouse model, feeding a prebiotic helped to mediate the bacterial changes caused by a high-fat diet, helping to reduce dysbiosis and associated inflammation. Furthermore, the prebiotic helped to reduce the weight gain caused by the high-fat diet. A meta-analysis published in mBio found a significant, albeit small, association between the diversity of the microbiome and the risk of being obese. However, researchers were not able to to determine if a person was obese solely by looking at the microbiome composition.

Other observational studies have found that antibiotic exposure (which is known to impact the microbiome and be associated with dysbiosis) during a child’s first six months of life was linked to a higher risk for being overweight. One study published in the International Journal of Obesity found an association between antibiotics and being overweight by the age of 7, especially in children of normal weight mothers. A similar study found that even after controlling for potential confounders, antibiotic exposure during the first six months related to an increased BMI in the first few years of life. Further studies also support this association, according to a review article published in the Nature Reviews Endocrinology.

Do Probiotics Help You Lose Weight?

While having a healthy gut microbiome may play a role in maintaining a healthy weight, unfortunately, it will take more than popping probiotics for weight loss or even having a fecal transplant to make any significant difference in your waistline.

In one systematic review of randomized controlled trials published in Endocrine Practice, the consumption of probiotics, whether in fermented foods or capsules, was found to have a significant impact on body weight, but only by a reduction of about three percent. To put that into perspective, in a 200-pound person, that would be six pounds, and it took at least eight weeks to see a result. While prebiotics did not have an impact on weight, they had other benefits, such as improving insulin sensitivity and reducing blood glucose levels. Another systematic review found inconsistent outcome with probiotics, although a few studies did have a positive result in which taking probiotics led to some weight reduction.

Human studies on probiotics and weight loss have yet to support recommending widespread supplementation. One study found that consuming 200 g per day of fermented milk containing a specific probiotic strain (Lactobacillus gasseri SBT2055) for 12 weeks significantly decreased the abdominal visceral and subcutaneous fat areas by an average of 4.6 and 3.3 percent respectively. There was also a 1.4 percent reduction in body weight and a 1.5 percent reduction in their body mass index (BMI). Again, these are significant but not clinically relevant. A 1.4 percent reduction of body weight in a 200-pound person would equate just 2.8 pounds reduction, although the decrease in abdominal fat may be more clinically significant.

A critical review published in the Nutrition & Metabolism journal found that other human clinical studies did not have significant results in terms of probiotics and weight loss, either. However, this is a new field, and more clinical studies will yield more insight into the role probiotics and the microbiome play in weight loss.

Meanwhile, the studies on prebiotics are more promising, according to one systematic review. Prebiotics are the fiber and other foods that nourish and fuel the beneficial bacteria in the gut, helping to promote a healthier microbiome. Many of the studies mentioned above also used prebiotics rather than probiotics to foster a positive impact.

There have also been studies into whether fecal microbiome transplantation (FMT) also known as gut microbiome transplantation (GMT) — experimental procedures in which a person’s microbiome is actually implanted with a healthier version — may help with obesity. Studies are looking into FMT and GMT for a wide range of diseases beyond obesity, although so far, it is only approved for c. diff infections.

In animal studies, microbiome transfusions have demonstrated alterations impacting weight. In one study, transfusion of an “obese microbiota” into germ-free mice made the mice more obese than the germ-free mice who were given “lean” microbiota, based on a study published in Nature. A similar study published in Science used human microbiome samples from twins and found that the germ-free mice with transplanted “obese microbiota” were more likely to become obese compared to those with the “lean microbiota.”

Although some studies have begun to look into the impact on humans, so far, the closest study published is a clinical trial that looked at insulin sensitivity but did not have sufficient evidence for the review of the impact on weight and body composition.  

So, do probiotics help you lose weight and what does this all mean? The connection between the gut microbiome and obesity, as well as probiotics for weight loss, remains in its early phases of research, but current conclusions do demonstrate there is some relationship between the two. Thus, it is beneficial to take steps to maintain a healthy gut microbiome.

Looking At Your Microbiome

You can start by taking a look at your current microbiome makeup. There are several tests on the market, some of which require a doctor’s order while others are direct-to-consumer. A few options include Viome, Ubiome, Diagnostic Solutions GI Map, and Genova Diagnostics Comprehensive Stool Analysis. Talk with your doctor or functional medicine practitioner for advice on the best one for you.

Other steps to take may include taking a high-quality probiotic, as well as consuming a healthy diet, reducing stress, and exercising. This will help to combat dysbiosis and its impact on your metabolism and appetite. However, simply popping a probiotic will likely not be enough for any substantial weight loss.

Everyone has different components potentially contributing to their weight gain beyond an imbalance of calories in and out and/or dysbiosis, such as hormonal imbalances or thyroid disorders or even mold. Therefore, it is always essential that you talk about any weight concerns and potential diet or exercise regime with your doctor, nutritionist, and/or healthcare professional before commencing probiotics for weight loss. Talking with your doctor can also ensure you are familiar with any potential risks to you for implementing any diet or lifestyle change, even one that is generally considered low-risk such as taking probiotics.

There are no guarantees that something that works for one or even the majority of individuals will work for you as well, and much of the research surrounding probiotics and weight loss remains in the research phase. Remember, obesity and associated conditions are complex; they do not develop overnight nor can they be fixed through one simple solution. In many cases, there are multiple factors involved, which also requires a long-term, multifaceted solution. Maintaining a healthy gut microbiome through diet, and potentially taking prebiotics and/or probiotics, may be an important component of any weight loss protocol.

Kendra Whitmire is the nutritionist at and owner of Sunshine Nutrition & Wellness. She has her master’s degree in Human Nutrition and Functional Medicine from the University of Western States. In addition to her work as a nutritionist, she is also a freelance writer. You can follow her on Facebook.

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