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Scientists find a hormone that makes you fatter


Our waistlines are expanding, it’s no secret that around the world despite rampant hunger people are also getting fatter. While there are many things that are contributing to this — our increased food security, the cost of food, fast food, the increasing sugar supplied in food, etc — there are other theories as to why we are getting so heavy. Scientists have pointed towards bacteria, gut microbiota, and many other causes for our increased weight, now add to that list a common hormone that we all produce.

Brown adipose tissue, widely known as “brown fat“, is located around the collarbone and acts as the body’s furnace to burn calories. It also keeps the body warm. Obese people have less of it, and its activity is decreased with age. Until now, researchers haven’t understood why.

There are two types of serotonin. Most people are familiar with the first type in the brain or central nervous system which affects mood and appetite. But this makes up only five per cent of the body’s serotonin.

The lesser-known peripheral serotonin circulates in the blood and makes up the other 95 per cent of the body’s serotonin. Researchers have discovered that this kind of serotonin reduces brown fat activity or “dials down” the body’s metabolic furnace.

The study is the first to show that blocking the production of peripheral serotonin makes the brown fat more active.

“Our results are quite striking and indicate that inhibiting the production of this hormone may be very effective for reversing obesity and related metabolic diseases including diabetes,” said Gregory Steinberg, the paper’s co-author.

(He is also co-director of MAC-Obesity, the Metabolism and Childhood Obesity Research Program at McMaster.)

“Too much of this serotonin acts like the parking brake on your brown fat,” he explained. “You can step on the gas of the brown fat, but it doesn’t go anywhere.”

The culprit responsible for elevated levels of peripheral serotonin may also have been found.

“There is an environmental cue that could be causing higher serotonin levels in our body and that is the high-fat western diet,” said Waliul Khan, co- author.

“Too much serotonin is not good. We need a balance. If there is too much, it leads to diabetes, fatty liver and obesity.”

The majority of serotonin in the body is produced by tryptophan hydroxylase (Tph1). The team found that when they genetically removed or inhibited this enzyme that makes serotonin that mice fed a high-fat diet were protected from obesity, fatty liver disease and pre-diabetes due to an enhanced ability of the brown fat to burn more calories.

Notably, inhibiting the peripheral serotonin doesn’t affect the serotonin in the brain or central nervous system functioning.

This is in contrast to earlier weight loss drugs which worked to suppress appetite by affecting levels of brain serotonin, but were associated with problems including cardiac complications and increased risk of depression and suicide.

“Moving forward, we think it’s a much safer method to work with increasing energy expenditure instead of decreasing the appetite, which involves more risks,” said Steinberg.

The researchers conclude that reducing the production of serotonin by inhibition of Tph1 may be an effective treatment for obesity and its comorbidities, and so the team is now working on a pharmacological “enzyme blocker.”

While drugs should never be substituted for eating healthy and exercise, some individuals due to health problems or age cannot exercise or simply do not know how to eat healthy. This could be the first step in a long line of things that could be done to help them get on the right track so to speak.

As a side note, it is sad that in the world today most of us are taught how to eat, but not what to eat. It’s because of this, fad diets like atkins or “gluten free” and people cannot understand why they can’t seem to get their weight under control.

Crane, J., Palanivel, R., Mottillo, E., Bujak, A., Wang, H., Ford, R., Collins, A., Blümer, R., Fullerton, M., Yabut, J., Kim, J., Ghia, J., Hamza, S., Morrison, K., Schertzer, J., Dyck, J., Khan, W., & Steinberg, G. (2014). Inhibiting peripheral serotonin synthesis reduces obesity and metabolic dysfunction by promoting brown adipose tissue thermogenesis Nature Medicine DOI: 10.1038/nm.3766

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