You’ve probably heard of serotonin, the neurotransmitter responsible for feelings of happiness and well-being. But you probably didn’t know that the serotonin in your brain — that which protects you from depression and anxiety and helps you feel content and happy — is only a small portion of the total serotonin within your body. Scientists from McMaster University have recently discovered that up to 95 percent of the serotonin in your body is peripheral serotonin — it works to stimulate your body’s natural brown fat deposits, controlling the rate at which your body burns white fat.
It’s this peripheral serotonin found in the blood that may be at the root of obesity in many Americans. Too much peripheral serotonin hampers brown fat activity, lowering the body’s metabolism. But blocking the action of that peripheral serotonin could boost metabolism, and without the dangerous side effects associated with appetite reduction drugs.
What Is Brown Fat?
Brown fat, once believed to be vestigial, has recently gained fame as the “good fat” that helps your body burn white fat stored as energy. Brown fat gets its name because of its reddish-brown color. Everyone is born with a fairly large amount of brown fat — a baby’s brown fat keeps him or her warm as well as lending to a cute, roly-poly appearance — but brown fat deposits in the body get smaller with age. That’s why metabolism tends to slow and extra weight becomes harder to keep off as you grow older. People suffering from obesity also have less brown fat than thinner people. Now, researchers are finally beginning to understand why.
Peripheral Serotonin Inhibits Brown Fat Activity
The McMasters University researchers have found an enzyme in the body, tryptophan hydroxylase or Tph1, is responsible for producing most of the peripheral serotonin that inhibits brown fat activity. This serotonin stops brown fat from working to burn white fat, the dangerous kind of fat that tends to accumulate around the hips, thighs, and abdomen. In an experiment, researchers blocked the action of Tph1 in mice eating a high-fat diet. They found that those mice demonstrated increased brown fat activity and a higher metabolism that protected them from obesity and its related health problems, including pre-diabetes and fatty liver disease. Mice with normal amounts of Tph1 gained weight as expected on the high-fat diet.
Study co-author Waliul Kahn believes that the high-fat Western diet may be triggering excess production of peripheral serotonin and, by extension, unnecessarily high levels of Tph1 in Americans. He told Medical News Today that the high-fat diet typical of Westerners today serves as an “environmental cue” that boosts peripheral serotonin production and impairs brown fat activity.
“Too much serotonin is not good,” he said. “We need a balance. If there is too much, it leads to diabetes, fatty liver and obesity.”
Could This Discovery Lead to New Obesity Treatments?
The good news is that the McMasters University researchers believe that this discovery could lead to new, more successful, and safer pharmacological treatments for overweight and obesity. By blocking the action of peripheral serotonin, researchers believe that they could successfully boost brown fat activity and speed metabolism for human beings suffering from obesity. Importantly, blocking the action of peripheral serotonin does not have an effect on the ability of serotonin to do its job within the brain. If you are currently using an antidepressant drug like Abilify, for example, there would be no concern that taking a weight loss drug to block peripheral serotonin would worsen your depression symptoms.
Nor would you have to worry about developing new depression symptoms while taking a weight loss drug designed to act on peripheral serotonin. That’s not the case with many of the weight-loss drugs currently on the market, which rely on suppressing appetite to achieve weight loss. For these drugs, depression is a side effect, along with heart problems and other dangerous complications. The researchers believe that a drug that boosts metabolism by increasing brown fat activity would be safer than a drug that merely suppresses appetite.
The drug is, however, still in development, and it’s likely that patients would still have to combine the drug with a healthy diet and regular exercise in order to achieve optimal weight loss. Researchers studying the effect of cold weather on brown fat have found that spending time in the cold can boost metabolism to help you burn 300 to 400 extra calories a day. While that’s not an insignificant amount, it’s not enough to lead to substantial weight loss unless other steps are taken.
Researchers at McMasters University think they have uncovered part of the reason why people suffering from obesity have so much trouble losing weight. The secret lies in peripheral serotonin. It’s the same hormone that, in the brain, regulates mood. In the body, however, it can dampen the fires of your metabolism, making weight gain easy and weight loss hard.