We once thought that weight loss was all about calories in, calories out, or just diet and exercise. Or perhaps, it’s in your genes or hormones like leptin. However, your gut bacteria might actually have more to do with your weight than you think. Read this post to learn about how probiotics could help you lose weight and improve your metabolism.

Why Do Probiotics help with Weight Loss?

1) Gut Bacteria of Obese People Can Harvest More Calories from Foods

In mice and rats, obesity-related microbes can harvest more energy from foods than the microbes that are found in lean animals [1].

Compared with lean mice with normal genes (wild-type), the gut bacteria of obese mice have more genes that can burn carbohydrates for energy [2].

2) Bacterial Metabolism and Metabolites Can Change Your Metabolism

How the gut bacteria metabolize primary bile acids to secondary bile acids affect our metabolism by activating the farnesoid X receptor, which controls fat in the liver and blood sugar balance [3].

Also, activation of bile acid receptors can increase metabolic rate in brown adipose tissues (fat that burns fat) [4, 5].

Intestinal microbiota can affect host adiposity and regulate fat storage [6].

In mice, diet accounts for 57% of changes in their gut microbiome [5].

3) Fecal Transplants Bring Along the Donor’s Metabolism

Gut bacteria from stools of healthy and lean humans transferred to obese people with type 2 diabetes increased insulin sensitivity and gut bacteria diversity [7]. However, this study did not observe significant changes in body mass index 6 weeks after the transfer.

In a case study, fecal matter was transplanted from an overweight donor to a lean patient for C. difficile infection treatment. After the transplant, the recipient had increased appetite and rapid unintentional weight gain that could not be explained by the recovery from the C. difficile infection alone [8].

In rats that are obese and insulin resistant, feeding them with antibiotics or transplanting them with fecal matters from healthy rats reversed obesity and insulin resistance [9].

In identical twin rats that have discordant phenotypes (e.g., one obese and one lean, despite identical genetics), it also appears that the gut bacteria control their metabolism. Germ-free mice (with no gut bacteria) populated with the obese twin had increased fat cells and reduced gut bacteria diversity compared to mice that were populated with the lean twin’s fecal matter [10].

In humans, more clinical studies would be necessary to determine whether fecal microbiota transplants can have long-term effects on insulin sensitivity or weight, even though fecal microbiota transplant can improve the gut microbiome for up to 24 weeks [11].

Presently, there are several phases 2 and 3 clinical trials for fecal microbiota transplant [12].

While results thus far have shown that fecal microbiota transplant is a promising therapy for metabolic problems, it does come with risks, including [12]:

  • Risks of infections getting carried over with the stool transplant
  • Known side effects include diarrhea or fever
  • Potential other negative traits or health problems could also be transferred along with the gut bacteria

4) Gut Bacteria Can Control Appetite and Satiety

Prebiotic fermentation by our gut bacteria increases gut hormones that increase appetite and glucose responses, including GLP-1 and peptide YY [13, 14].

5) Reduces Inflammation from Leaky Gut

Weight gain is associated with leaky gut (intestinal permeability) because high-fat diets can lead to leaky gut and thus circulating lipopolysaccharides in the bloodstream [15]. This is called metabolic endotoxemia.

Metabolic endotoxemia can result in chronic, low-grade inflammation as well as increased oxidative damage that increases cardiovascular risks [16].

In a clinical trial with probiotic as an intervention for metabolic syndrome, the probiotic treatment led to a significant reduction in tissue inflammation and leaky gut due to a high-fat diet (metabolic endotoxemia) [17].

Bacteroidetes vs Firmicutes – The Obese vs Lean Link?

Bacteroidetes and Firmicutes phyla (groups) comprise ~90% of the human gut bacteria [18].

In one small study, Bacteroidetes positively correlated with weight loss in obese humans [19].

A larger study in humans found that obesity was indeed associated with [2]:

  • reduced levels of Bacteroidetes
  • reduced bacteria density
  • more bacteria genes that metabolize carbohydrates and fats for energy

Studies in mice and rats also confirmed the link between Bacteroidetes and leanness. Bacteroidetes are also more abundant in lean animals, while Firmicutes are more abundant in their obese counterparts [20, 21, 22]. However, in these studies, it was unclear whether the obesity-inducing high fat diet caused the bacteria predominance or the bacteria caused the obesity.

Interestingly, mice that have 2 copies of the leptin gene also have a 50% reduction in Bacteroidetes [23], suggesting that obesity may also change the gut bacteria composition.

Note: Lactobacilli, Streptococci, and Staphylococci are Firmicutes, whereas Bifidobacteria are actinobacteria, which are neither Firmicutes or Bacteroidetes.

Although a number of Firmicutes (like lactobacilli) in the gut seems to correlate with obesity, in many cases, supplementation with Lactobacilli helped with weight loss.

Probiotic Strains for Weight Loss and Metabolic Health

Consuming probiotics can reduce body weight and BMI. A greater effect is achieved in overweight subjects, when multiple species of probiotics are consumed in combination or when they are taken for more than 8 weeks [24].

Mixed Probiotic Blends and Weight Loss

L. acidophilusB. animalis ssp. lactis and L. casei reduced BMI, fat percentage, and leptin levels in overweight individuals [25].

Oral administration of B. longumB. bifidumB. infantis, and B. animalis decreased glucose levels, ameliorated insulin resistance, and reduced the expressions of inflammatory adipocytokines in obese mice [26].

In obese children, the intake of synbiotics (probiotics + prebiotics) resulted in a significant reduction in BMI, waist circumference, and some cardiometabolic risk factors, such as total cholesterol, LDL-cholesterol, and triglycerides [25].

Several studies have demonstrated that individual probiotic bacteria strains can help with weight loss. However, many of these are observational in nature, while others were done in animals.

Probiotic and Weight Loss Tested in Humans

Bifidobacterium animalis and Weight

Humans with more B. animalis have lower BMI, while those with less of this bacteria have higher BMI [2728].

Daily ingestion of milk containing B. animalis ssp. lactis significantly reduced the BMI, total cholesterol, low-density lipoprotein, and inflammatory markers in humans [29].

Bifidobacterium breve (B-3) Improves Metabolism and Reduces Belly Fat

B. breve lowered fat mass and improved GGT and hs-CRP in adults with obese tendencies [30].

B. breve reduced weight and belly fat in a dose-dependent manner. It also reduced total cholesterol, fasting glucose, and insulin in a mice model of diet-induced obesity [31].

Lactobacillus gasseri BNR17 (BNR17 and SBT2055) [32, 33]

  • decreased body weight
  • reduced waist and hip circumference
  • reduce belly fat and fat under the skin in adults with obese tendencies

However, constant consumption of this probiotic may be required to maintain this effect [33].

Both L. rhamnosus and L. gasseri also significantly lowered weight in mice [343536], while L. gasseri also reduced body weight in rats [37].

Lactobacillus paracasei Reduces Food Intake and Body Weight

L. paracasei decreases energy/food intake in both humans and animals [38].

Water extract of L. paracasei reduced body weight in obese rats. It decreased the formation of lipid plaques in the aorta, reduced fat cells size, and inhibited fat absorption, thereby reducing fat production (lipogenesis) [39].

Lactobacillus Plantarum (PL60 and PL62) Burns Fat

L. Plantarum PL60 and PL62 produce a fatty acid called conjugated linoleic acid (CLA), which can help increase fat burning in mice. After 8 weeks of feeding, L. rhamnosus PL60 reduced body weight without reducing caloric intake as well as white fat tissues [40, 41].

A low-calorie diet supplemented with L. plantarum reduced BMI in adults with obesity and hypertension [25].

Lactobacillus rhamnosus (CGMCC1.3724)

  • induced weight loss 
  • reduce fat mass
  • reduces circulating leptin concentrations
  • improved liver parameters in obese children with liver dysfunction noncompliant with lifestyle interventions [42, 43].

Lactobacillus salivarius Ls-33 Shifts the Microbiota Towards Lean Bacteria

In obese adolescents, introducing L. salivarius Ls-33 increases groups of bacteria, like Bacteroidetes to Firmicutes ratio [44].

Clostridium butyricum (CGMCC0313.1, tested in mice)

C. butyricum reduced fat accumulation in liver and blood, lowered insulin levels, and improved glucose tolerance and insulin sensitivity in obese mice. Furthermore, C. butyricum administration ameliorated GI and fat tissue inflammation [45].

Probiotics Associated with Weight Gain

source: http://www.sciencedirect.com/science/article/pii/S0882401012001106

Avoid these if you are trying to lose weight [46]:

  • Lactobacillus acidophilus – in both humans and animals
  • Lactobacillus fermentum – in animals
  • Lactobacillus ingluviei – in animals
  • Lactobacillus reuteri – in humans, although it helps with some obesity-related symptoms [47].

Further Reading

For technical information, check individual probiotic chapters:

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About the Author

Nattha Wannissorn - PHD (MOLECULAR GENETICS) - Writer at Selfhacked

Nattha Wannissorn, PhD

PhD (Molecular Genetics)

Nattha received her Ph.D. in Molecular Genetics from the University of Toronto and her undergraduate degree in Molecular and Computational Biology from the University of Pennsylvania.

Aside from having spent 15 years in biomedical research and health sciences, Nattha is also a registered holistic nutritionist, a certified personal trainer, has a precision nutrition level 1 certification, and is a certified functional diagnostic nutrition practitioner. As a holistic practitioner with a strong science background, Nattha is an advocate of science literacy in health topics and self-experimentation.

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