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Your Sweet Tooth Is Actually in Your Liver

It produces a hormone that functions like a candy stop sign.

by Jesse Hicks
May 2 2017, 5:54pm

Clem Onojeghuo/Unsplash

If you find yourself reaching for yet another handful of M&Ms, new research suggests a surprising culprit. It turns out that the ole "sweet tooth" might actually be a hormone secreted by the liver, which affects consumption of candy and other sweets. More broadly, the finding hints at an overlooked regulatory system that may influence our eating decisions more than we knew.

Researchers at the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen examined variations in a hormone called FGF21 which the liver releases after eating sweets. (The liver is the next organ nutrients hit after food goes through the stomach and intestines.) Previous studies had shown that the hormone regulated consumption of sweets in rats and suppressed sugar cravings in primates primates, but it wasn't known whether it played a similar role in humans—that is, telling your body it's time to put the candy away.

The researchers drew from a survey of the lifestyles and metabolic health of 6,500 Danish people and sequenced the FGF21 gene in all participants. They specifically looked at two variants of the gene that had been linked to increased carb intake and found that people with those two variants were about 20 percent more likely to be the biggest eaters of sweet stuff. (The variants were also associated with increased alcohol intake and smoking, though that aspect of the study requires more research.)

The next step for researchers was to figure out just how FGF21 worked within the body, so they monitored people before and after they ate sugar. Specifically, they sorted a group of 51 people into those who really, really liked sweets and those who could care less about them. These people fasted for 12 hours and then researchers drew their blood. They found the sweet-shunning group had 50 percent higher FGF21 hormone levels than the sweet-tooth group, which supports the idea that the hormone keeps sugar cravings at bay. Interestingly, after consuming sugary water that was the equivalent of two cans of soda, everyone's FGF21 blood levels (the sugar "stop sign") rose to about the same level. The study was published in the journal Cell Metabolism.

The findings suggest a complex dynamic between the liver, the hormones it secretes, and how we eat. It may not just be sugar consumption, after all, that's regulated by the liver—the body could be relaying many signals about the amount and kind of nutrients it needs.

To dig deeper into that question, researchers want to do a larger follow-up study to see how FGF21 works in different individuals. That could lead to the discovery of more variant genes and possible associations with metabolic conditions such as obesity or type 2 diabetes. In the meantime, you can maybe blame your liver for your 4pm candy breaks.

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