Caloric Restriction Works Beyond Weight Loss, Alters Gut Microbiome
Low-calorie diets are popular and fairly effective weight loss strategies. However, severe caloric restriction has more effects on the human body than just fat loss. It contributes to drastic changes in physiology, immune response, metabolism, and gut health.
Recent work on the extensive microbiome population in the human gut has shown that they play a crucial role in regulating major aspects of our health, so much so that some call the gut the ‘second brain.’ Maintaining a healthy balance of microbes has been shown important for metabolism, mental health, immune response to disease, and medication.
Low-Calorie Diet Reduces Gut Microbiota
A recent study, published in Nature, explored the effect of low-calorie diets on the composition of the microbiome in the gut. Post-menopausal obese/overweight women were put on a 12-week low-calorie liquid diet followed by a 4-week recovery period and compared with women on a normal diet.
As expected. a low-calorie diet resulted in an average of 13% weight loss. Observing the difference in composition and activity of gut microbiome between low-calorie and normal diets, scientists from the University of California, San Francisco, and Universitätsmedizin Berlin found that low-calorie diets decreased the overall amount of gut bacteria. There was a slight change in composition as a low-calorie diet increased bacteria that breakdown glycans, decreased those that utilize plant polysaccharides. These changes were reversed when the women were taken off the diet.
Change in Microbiome Contributes to Weight Loss
When the gut microbiome from participants on a low-calorie diet was transplanted to sterilized mice on a normal diet, mice that received post-diet microbes lost more weight when compared to those that received pre-diet microbes. This suggests that a change in their gut microbiome composition contributed to weight loss. Upon sequencing the gut microbiomes from mice with pre-diet and post-diet transplants, the team found an increase in the bacterial species Clostridium difficile, a pathogenic bacterium implicated in inflammation and colitis.
Clostridium difficile is known to metabolize fats, and an increase in its population has been linked to severe inflammation and diarrhea. However, in the mice transplanted with post-diet microbes with a high concentration of Clostridium difficile, there was no major inflammation, suggesting that C.difficile has an additional role in fat metabolism.
While it is an interesting observation, the authors are cautious about its interpretation. “Let’s be clear; we are definitely not promoting C. difficile as a new weight loss strategy. We’ve got a lot of biology left to unpack here,” said co-lead author Dr. Peter Turnbaugh, Ph.D., Associate Professor of microbiology and immunology at UCSF. More work would be required to understand the effect of long-term calorie deficits and the levels of C. difficile, which could trigger severe inflammation.
The study shows that calorie management has more effects than just weight loss and the gut microbiome plays a role in either enhancing or hindering weight loss. Further work on which species contribute to weight loss could help clinicians alter the gut microbiome accordingly to help patients achieve better results.
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