Researchers are one step closer to understanding how changes in the gut microbiome lead to obesity.
A University of Iowa study determined that the gut microbes of people taking risperidone, an antipsychotic drug that causes weight gain, were significantly altered. They dug a little deeper and found that, in mice, the weight gain was caused by a decrease in the resting metabolic rate
(a measure of the amount of energy used when at rest, especially while sleeping).
Weight gain in the risperidone-treated mice was, on average, equivalent to 10% of total body mass, and the drug altered the composition of gut bacteria. These results backed previous studies in humans. According to study author John Kirby, “the control mice gain a little weight as they age and their microbiome undergoes a 'healthy shift' due to aging. With the risperidone, the mice become obese and exhibit an alternative, less healthy shift in their microbiome”.
They measured the aerobic and anaerobic resting metabolic rates of the mice using a “total calorimetry machine”. They did not find a significant change in the aerobic rate, but found a 16% decrease in the resting aerobic rate of risperidone-treated mice. For a human, such a change translates to a weight gain of 29 pounds a year!
Finally, they showed that the altered microbiome itself was responsible for the weight gain. They transferred gut microbes from risperidone-treated mice into control mice and saw the same decrease in resting metabolic rate, as well as the associated weight gain.
What’s more, they could recreate the changes in metabolic rate and weight by transferring only bacteriophage from the risperidone-treated mice into control mice. This finding alone demonstrates just how complex the microbiome really is!