Gimmicky diets, flavor fakery, and sham sweets all try to bamboozle the brain out of wanting sugary treats and calorie-packed happy hour drinks. But scientists may have found an all-natural way to simply switch off those corrupting cravings.

When researchers gave mice and monkeys an added dose of a mammalian liver hormone called Fibroblast growth factor 21 (FGF21), both species voluntarily went off sweets, even artificial ones. And mice previously hooked on alcoholic beverages were more content with plain water after the hormone therapy. The results, published in the journal Cell Metabolism, follow a series of studies that suggest FGF21 is a key metabolic regulator that may be helpful in treating obesity and type 2 diabetes. Clinical trials are already underway.

Those previous studies suggested that FGF21, made mostly in the liver but also in fat tissue and the pancreas, can help regulate glucose and lipid metabolism in the body. Many food inputs and hormonal cues, some complex, some simple, can tweak metabolism. Studies suggested that FGF21 gets involved by crossing the blood-brain barrier and grabbing onto a specific complex of proteins on the outside of cells in the central nervous system. By clamping on, the hormone can activate signals within the brain that ultimately alter food intake.

From experiments with obese mice, monkeys, and humans, scientists knew that added doses of FGF21 led to weight loss and improved insulin sensitivity, which is critical for maintaining healthy blood sugar levels and treating type II diabetes. In other studies, researchers found that some of the differences in people’s preferences for sweets and carbohydrates boiled down to DNA differences in and around the gene that encodes FGF21.

In the new study, researchers led by David Mangelsdorf and Steven Kliewer at the University of Texas Southwestern Medical Center took a closer look at what happens when FGF21 reaches cells in the central nervous system. Using mice, the researchers found that FGF21 caused a decrease in dopamine in the nucleus accumbens, a part of the brain that, in part, processes pleasure, addiction, and motivation. Dopamine is a powerful neurotransmitter involved in reward-motivated behaviors, such as cravings for sugary, high-calorie treats. Thus, FGF21 may manipulate the pleasure responses and desires for certain sugar-based food.

Giving the mice an option of candied water (containing sugar or an artificial sweetener) or regular water, researchers found that FGF21 suppressed their interest in syrup swigging. The hormone didn’t alter the rodents’ interest in bitter foods, fatty acids, nor their performance on behavior tests that examine unhappiness. In obese cynomolgus monkeys, added FGF21 also had a dampening effect on sugar consumption.

Because dopamine regulates alcohol cravings in addition to sugary ones, the researchers tested out the hormone treatment in mice that had been hooked on water spiked with ethanol. Just as in the sugar tests, the researchers found that FGF21 also suppressed cravings for mousey cocktails.

The authors conclude that their findings may suggest a "feedforward regulatory pathway" for limiting consumption of sugars and alcohol. Because FGF21 production is known to naturally dial-up in the bodies of mice and humans after they eat carbohydrates, the hormone may act as a built-in shut-off switch—one that may be exploitable, though it may be hard to disentangle from the complex network of controls that interlink pleasure and food.

The authors call for more studies into how FGF21 can regulate food cravings in people, in addition to the clinical trials already in progress.

Cell Metabolism, 2015. DOI: 10.1016/j.cmet.2015.12.008 (About DOIs).