We've made it through the food and drink excesses of the holiday season and many of us are now seeking a healthier start to the new year – and it appears a key factor in reigning in the sweet tooth could be coming from your liver.
Two new studies have found that a hormone produced by our livers called fibroblast growth factor 21 (FGF21) helps to regulate the intake of both sugars and alcohol in mice, and the same pathway might be able to suppress the appetite for sweet treats in humans.
"This is the first liver-derived hormone we know that regulates sugar intake specifically," said Matthew Potthoff, a pharmacologist at the University of Iowa.
Fibroblast growth factor 21 is produced in the liver in response to high carbohydrate levels. From there, it enters the bloodstream and sends a signal to the brain to suppress the appetite for sweetness.
In testing with mice, animals injected with FGF21 were given a choice between a normal diet and a sugar-enriched diet. While the mice continued to eat sugar, they ate seven times less than the control group.
In addition to experiments with normal healthy mice, the researchers also studied two kinds of genetically-modified animals: mice that didn't produce FGF21 at all, and mice that produced 500 times more FGF21 than normal mice.
When given the same choice between a normal diet and a sugar-enriched diet, the mice lacking FGF21 ate more sugar, and the mice with high FGF21 levels ate less sugar.
While FGF21 decreases appetite and intake of sugar in mice, it doesn't impact consumption of complex carbohydrates, proteins, or lipids. It also affects appetite for different sugars (for example, sucrose, fructose, and glucose) at different rates.
"We've known for a while that FGF21 can enhance insulin sensitivity," said one of the team, Lucas BonDurant. "Now, there's this dimension where FGF21 can help people who might not be able to sense when they've had enough sugar, which may contribute to diabetes."
A separate study led by researchers at the University of Texas Southwestern Medical Centre (UT Southwestern) reported similar results of suppressed appetite for sweet foods when studying FGF21 in mice and monkeys, and also found that the hormone curbed the mice's consumption of alcohol-laced water.
If this latter effect can be replicated in humans – and that's a big "if" - it could lead to new avenues of treatment for people who experience problems with alcohol.
The UT Southwestern study also found that mice with elevated levels of FGF21 showed a marked decrease in levels of dopamine, a neurotransmitter that plays a central role in reward behaviour.
"Our findings raise the possibility that FGF21 administration could affect nutrient preference and other reward behaviours in humans, and that the hormone could potentially be used to treat alcoholism," said Steven Kliewer, a molecular biologist and pharmacologist at UT Southwestern.
It's not yet fully understood what the purpose of FGF21 in animals is – whether it's to somehow improve diet quality, or perhaps act as a defensive compound to help protect the liver from overconsumption of harmful substances. But further study could help us understand better what's going on here and how we can improve our health as a result.