While sugar cravings are common, the physiological mechanisms that trigger our “sweet tooth” are not well defined.
A University of Iowa-led study in mice shows that a hormone produced by the liver, fibroblast growth factor 21 (FGF21), suppresses the consumption of simple sugars.
The researchers report that FGF21 is produced in the liver in response to high carbohydrate levels. FGF21 then enters the bloodstream, where it sends a signal to the brain to suppress the preference for sweets.
Says Matthew Potthoff, assistant professor of pharmacology in the UI Carver College of Medicine:
“This is the first liver-derived hormone we know that regulates sugar intake specifically."
Potthoff is co-senior author on the paper with Matthew Gillum, professor at the University of Copenhagen.
Enhanced Insulin Sensitivity
Previous research explains how certain hormones affect appetite; however, these hormones do not regulate any specific macronutrient (carbohydrate, protein, fat) and are produced by organs other than the liver.
The research could improve diet and help patients who are diabetic or obese. Says Lucas BonDurant, a doctoral student in the Interdisciplinary Graduate Program in Molecular and Cellular Biology and co-first author in the study:
“We’ve known for a while that FGF21 can enhance insulin sensitivity. 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."
This work is based on human genome-wide studies where researchers found associations between certain DNA mutations and people’s intake of specific macronutrients. Two of these mutations were located near the FGF21 gene, prompting the UI-led team to identify the role of this hormone in regulating macronutrient preference.
Seven Times Less Sugar
BonDurant and colleagues used genetically-engineered mouse models and pharmacological approaches to examine the role of FGF21 in regulating sugar cravings. In normal mice, BonDurant injected FGF21 and gave the mice a choice between a normal diet and a sugar-enriched diet.
Researchers observed that the mice didn’t completely stop eating sugar, but they ate seven times less than normal.
The research team also studied genetically-modified mice that either didn’t produce FGF21 at all or produced a lot of FGF21 (over 500 times more than normal mice). The genetically-modified mice had a choice between the same two diets as the normal mice.
Researchers observed that the mice that didn’t produce FGF21 at all ate more sugar, whereas the mice that produced a lot of FGF21 ate less sugar.
[caption id=“attachment_24788” align=“aligncenter” width=“640”] Credit: University of Iowa[/caption]
FGF21 also doesn’t impact the intake of complex carbohydrates.
While BonDurant found that FGF21 sends signals to the brain, additional work is necessary to identify the precise neural pathways that regulate FGF21’s ability to manage macronutrient preference. UI researchers are focused on the hypothalamus— a section of the brain responsible for regulating feeding behavior and energy homeostasis.
“In addition to identifying these neural pathways, we would like to see if additional hormones exist to regulate appetite for specific macronutrients like fat and protein, comparable to the effects of FGF21 on carbohydrate intake,” Potthoff says. “If so, how do those signals intertwine to regulate the neural sensing of different macronutrients?"
von Holstein-Rathlou and BonDurant et al. FGF21 Mediates Endocrine Control of Simple Sugar Intake and Sweet Taste Preference by the Liver Cell Metabolism, dx.doi.org/10.1016/j.cmet.2015.12.003
Top Image: Glucose. Stefan Eberhard, Wellcome Images