Sweet tooth / carbohydrate preference (FGF21)

FGF21 is a hormone that helps dial down cravings for sweets and carbs. A common variant near the FGF21 gene is linked to a slightly stronger preference for sugary and carb-rich foods. The effect is small, and habits matter far more.

What FGF21 does

FGF21 is a hormone the liver releases in response to carbohydrate, and one of its jobs is to signal the brain to reduce sweet intake. It is a satiety signal specific to sugar rather than to food in general, which is unusual and part of why it draws so much research attention.

This variant is associated with the sweet side of that loop: carriers of one version report consuming more sugar, which fits a slightly weaker brake.

How large the effect is

Small. In a study of 159,527 people, the association with taste liking had a beta of 0.046, meaning a very slight shift in reported preference per copy. The p-value is convincing because the sample is enormous; the effect on any individual is not.

The counterintuitive part is what does not follow. Despite associating with higher sugar consumption, this variant has not been linked to higher body weight in the way that would be expected, and some studies report associations with lower body fat and higher blood pressure instead. The pathway is more complicated than a sweet-tooth gene.

The frequency makes the label awkward

In 1000 Genomes reference data, about 99% of East Asian-ancestry individuals carry two copies of the allele associated with higher sugar intake, against roughly 31% of European-ancestry individuals.

A variant carried by essentially the entire population of one region cannot be a meaningful explanation for individual sweet preference, and it is a good example of why frequency should always be checked before a variant is described as a trait gene.

What this variant does not tell you

Sugar consumption is shaped by availability, price, marketing, habit, sleep and stress far more than by a single hormone variant with a beta of 0.05. Nothing here supports a dietary decision.

What each rs838133 genotype means

rs838133 has three possible genotypes: AA, AG and GG.

Lower sweet preference (FGF21) (rs838133 AA). You don't carry the FGF21 sweet-preference variant, so as far as this gene goes, you lean toward a slightly lower pull from sugary and carb-rich foods. Many things shape what you crave, so this is just one small input.

Mild sweet preference (rs838133 AG). You carry one copy of the FGF21 variant linked to a slightly stronger liking for sweet and carb-rich foods. It's a small nudge, and your habits and environment matter far more.

Sweet tooth tendency (FGF21) (rs838133 GG). You have two copies of the FGF21 variant linked to a stronger preference for sugary and carb-rich foods. It's a real but small genetic nudge toward a 'sweet tooth', easily outweighed by habit, so it's helpful to know rather than something to worry about.

Evidence & sources

Across global populations, about 37% of people carry two copies of this variant, and about 17% carry none.

This variant appears in 5 published genetic studies: PubMed 23372041 · PubMed 29988085 · PubMed 32393786 · PubMed 34426670 · PubMed 35585065.

Common questions

Do I have a sweet tooth gene? This variant nudges reported sugar intake by a very small amount in very large studies, and nearly everyone of East Asian ancestry carries it. It is real at population scale and close to meaningless at personal scale.

Related

Alcohol response (flushing & dependence risk) · Beta-carotene to vitamin A conversion (BCO1) · Caffeine metabolism speed · Fat taste sensitivity (CD36) · Omega-3/6 conversion efficiency · Secretor status (norovirus resistance & B12) · Total cholesterol