A liver-derived hormone may tell us when we have had enough sweet food.
Over 50 years ago, the liver was already thought to have an important role in regulating food intake and preference. Previous work has also shown that FGF21 (or fibroblast growth factor 21), a hormone derived from the liver, plays a part, and that variations in the FGF21 gene sequence can cause humans to have preferences for different macronutrients.
Now, two new studies have shed new light on the FGF21 hormone and how it works.
Matthew Potthoff, of the University of Iowa, and Matthew Gillum, of the University of Copenhagen, worked together on one study to investigate the function of FGF21.
They wanted to look at the mechanisms that regulate sugar appetite after consumption, and to do this, they decided to study the role of FGF21 in regulating food preference.
FGF21 affects behavior by acting on central nervous system
They carried out experiments on mice to see how FGF21 regulates intake of alcohol and sugar.
Through their experiments, they observed that the liver produces FGF21 in response to sugar intake. FGF21 then enters the bloodstream and selectively represses sugar appetite by acting on the hypothalamus, the part of the brain that regulates food intake and energy homeostasis.
Meanwhile, at the University of Texas, researchers led by Steven Kliewer and David Mangelsdorf looked at FGF21 in mice and monkeys.
FGF21 was seen to influence sweet and alcohol preference. When a single dose was given to a monkey, the monkey lost interest in sweet water; similar tests showed a decreased interest in alcohol.
Other tests, however, indicated that FGF21 does not affect responses to fatty acids or bitter taste.
The studies, together with human genetics studies linking FGF21 to nutrient preference, show that the FGF21 can affect behavior by acting on the central nervous system. They also add to the growing evidence that controlling appetite is a whole-body affair.
Why FGF21 exists is still not entirely clear. It may be to improve diet quality, or, since sugar can ferment into ethanol, perhaps to help the liver protect itself from excess alcohol.
However, Kliewer cautions:
"While at first blush it would seem that this FGF21-regulated pathway could be a panacea for suppressing sugar and alcohol consumption, it's important to keep in mind that these reward behaviors are closely tied to mood, and so additional studies to determine if FGF21 causes depression are certainly warranted."
Potthoff would also like to investigate whether, in addition to FGF21, which affects carbohydrate intake, there are additional hormones that regulate appetite for specific macronutrients like fat and protein, and if so, how those signals interact to regulate the neural sensing of different macronutrients.
Earlier this year, Medical News Today reported that hormonal therapy that suppresses appetite might help people to lose weight.