Probiotics are bacteria that have health benefits when consumed. They are found in probiotic supplements and some fermented foods.
Several studies indicate that probiotics can be useful in the battle against weight gain and obesity (1).
This study examined the effects of a broad-spectrum probiotic supplement on weight gain during a high-fat, high-calorie diet.
People who have obesity and/or type 2 diabetes may have more undesirable bacteria in their digestive system than beneficial bacteria (2).
Although the cause of this imbalance is not entirely clear, evidence indicates that high-fat, high-calorie diets may cause unfavorable changes in the bacterial environment in the gut (3).
For this reason, dietary strategies that positively affect the gut bacteria may potentially benefit people with obesity or metabolic diseases.
One such strategy is supplementation with probiotic bacteria, like Lactobacillus and Bifidobacterium.
Previous studies have shown that probiotics may decrease the growth of undesirable bacteria and reduce inflammation in the digestive system (7).
Researchers at Virginia Tech set out to examine whether a probiotic supplement would reduce weight gain on a high-fat, high-calorie diet.
Basic Study Design
This was a 4-week, double-blind, randomized controlled trial in 20 healthy, non-obese men, aged 18–30 years.
The participants were randomly assigned to one of two groups:
- Probiotic group: Participants received a broad-spectrum probiotic supplement called VSL#3. Two doses of VSL#3, each containing 450 billion probiotics of 8 different strains, were consumed daily in a milkshake.
- Placebo group: Participants in the placebo group received milkshakes containing cornstarch instead of probiotics.
All participants were also put on a weight-gain diet, containing an excess of 1000 calories. This diet was high in fat, containing 55% fat, 30% carbs and 15% protein.
Several variables were measured at the beginning and the end of the study; these included body composition, insulin sensitivity, endotoxins and inflammatory markers.
Bottom Line: This was a 4-week, randomized controlled trial in 20 healthy, non-obese men. They were assigned to one of two groups: probiotic supplementation and placebo.
Finding 1: Probiotic Supplementation Reduces Weight Gain
The probiotic supplementation reduced gain in body mass and fat mass, compared to the placebo.
The chart below shows the difference in weight gain between groups.
An additional study showed that taking probiotic supplements might reduce weight gain during 7 days of overfeeding (10).
The present study shows that these effects are sustained for up to 4 weeks.
Further studies are needed to determine exactly how this works.
Bottom Line: Probiotic supplements reduced gain in body mass and fat mass in people who were fed a high-fat, high-calorie diet.
Finding 2: Effects on Insulin Sensitivity
The high-fat, high-calorie diet did not affect insulin sensitivity in the participants.
However, they conflict with one study showing that probiotic supplementation may prevent development of insulin resistance during 7 days on a high-fat, high-calorie diet (10).
The reason for this inconsistency is unclear.
Bottom Line: Neither the high-fat diet nor the probiotic supplements had any effects on insulin sensitivity. Other studies have provided mixed results.
Finding 3: Effect on Endotoxins
Endotoxins, also known as lipopolysaccharides, are found in the membranes of some gut bacteria.
These compounds may find their way into the blood circulation of individuals with an imbalance in the bacterial environment in the gut.
In the present study, the levels of endotoxins did not change in either group.
Bottom Line: A high-fat, high-calorie diet did not affect levels of endotoxins in blood. Probiotic supplementation did not affect endotoxins either.
Finding 4: Effect on Inflammation
Systemic inflammation is estimated by measuring inflammatory markers in the blood.
The present study measured three inflammatory markers: C-reactive protein (CRP), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α).
TNF-α increased significantly in both groups during the 4 weeks of the high-fat, high-calorie diet.
CRP did not change significantly during the study period. IL-6 seemed to increase, but the change was not statistically significant.
Probiotic supplementation had no effects on the change in inflammatory markers.
Bottom Line: The high-fat, high-calorie diet increased levels of TNF-α, a marker of inflammation. Probiotic supplementation did not affect this increase.
The study was well designed. However, as in most studies, there were a few important limitations.
For starters, the number of participants was low. A larger number of participants would have increased the statistical power of the study.
Second, the study included only healthy, non-obese men. For this reason, the results cannot be generalized. The effects might be different in obese people or women.
The probiotic supplement also contained multiple strains of bacteria, which may have different effects on health. For this reason, it is unclear which probiotic bacteria were responsible for suppressing weight gain.
Bottom Line: This study was well designed and conducted. However, the number of participants was low and the findings may not apply to women or people with obesity.
Summary and Real-Life Application
This study evaluated whether probiotic supplements would help protect against the adverse effects of consuming a high-fat, high-calorie, weight-gain diet.
Neither the diet nor the probiotics had significant effects on insulin sensitivity or endotoxin levels.
The diet did cause an increase in one inflammatory marker, but the probiotics did not have any effect.
However, this study did show that people who took a probiotic supplement gained significantly less weight and fat mass. This indicates that probiotics may be an effective way to prevent weight gain and obesity.
Probiotics may even be useful for weight loss if the diet is not hypercaloric, but the current study did not test that.