FGF21 Gene Variants, Diet Preferences, and Metabolism

Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

This article is part of the PlexusDx Education Hub — your resource for evidence-based guidance on diet & genetics. Browse all Diet & Genetics education

Why do some people crave sweets and carbohydrates while others reach for protein or fat without a second thought? Part of the answer is written in a gene called FGF21. Variants in and near this gene influence how your brain and body regulate appetite, macronutrient preference, and energy metabolism — and they help explain why no single diet works for everyone.

What FGF21 Does in the Body

FGF21 (fibroblast growth factor 21) is a hormone produced mainly by the liver in response to fasting, carbohydrate intake, and metabolic stress. It acts on the brain, fat tissue, and pancreas to help regulate glucose handling, insulin sensitivity, and how the body partitions energy. Because it signals directly to reward and appetite centers, FGF21 sits at the crossroads of what you eat and how your metabolism responds.

The rs838133 Variant and Your Preference for Sugar

The most studied FGF21 variant is rs838133. Large population studies have linked the A allele of rs838133 to higher consumption of sugar, carbohydrates, and even alcohol. Counterintuitively, the same carbohydrate-seeking allele has been associated with slightly lower body-fat percentage in some cohorts, likely because macronutrient preference and total energy balance are not the same thing. A related variant, rs838145, shows similar associations. These are common variants — the sweet-preference allele appears in a large share of the population.

FGF21, Macronutrient Balance, and Metabolism

FGF21 does not just nudge cravings; it participates in the feedback loop between diet and metabolic rate. When protein intake is low or carbohydrate intake is high, FGF21 levels rise and signal the brain to adjust intake. Variants that change FGF21 signaling can subtly shift where your set point for carbohydrate and protein lands, which affects satiety, snacking patterns, and how satisfied you feel after a meal. Understanding this tendency is more useful than fighting it blindly.

This links to the popular idea of protein leverage — the observation that people tend to keep eating until a protein target is met, sometimes overshooting on calories from carbohydrates and fat along the way. FGF21 is one of the hormonal signals thought to sit inside that loop. For someone whose genetics tilt toward carbohydrate preference, prioritizing adequate protein at meals can be a practical, evidence-aligned way to support fullness without relying on willpower alone.

What the Research Shows

In genome-wide analyses of dietary macronutrient intake, researchers identified the FGF21 locus as one of the strongest genetic signals for carbohydrate and sugar preference. Follow-up studies tied FGF21 signaling to alcohol and sweet-taste behavior in both humans and animal models. The effect size for any single variant is modest — genetics sets a tendency, not a destiny — but across a population the signal is clear and reproducible.

Genes Rarely Act Alone: FGF21, FTO, and MC4R

FGF21 is one node in a network. The FTO gene influences overall appetite and energy intake, while MC4R helps regulate hunger and satiety through the melanocortin pathway. A person carrying the carbohydrate-preferring FGF21 allele plus a higher-appetite FTO profile may experience cravings differently than someone with only one of these variants. Looking at these genes together gives a more complete picture than any single result.

What Your Genetic Insights Reveal

The Precision Peptide Genetic Test analyzes 14 pathways, 49 peptides, 150+ genetic insights, including variants that shape appetite regulation, macronutrient preference, and metabolic signaling. Rather than prescribing a diet, it shows you the biological tendencies you are working with — so a conversation with a registered dietitian or physician can start from your actual genetics instead of trial and error. Genetics is a guide, not a guarantee.

Frequently Asked Questions

Does the FGF21 gene make me crave sugar?

FGF21 variants such as rs838133 are associated with a stronger preference for sugar and carbohydrates, but they do not force a specific diet. Your environment, habits, sleep, and stress all shape cravings too. Genetics describes a tendency you can work with, not an outcome you cannot change.

Can I change how my FGF21 gene affects me?

You cannot change your DNA sequence, but you can influence how genes express through diet, protein intake, sleep, and physical activity. Knowing your FGF21 tendency helps you build eating patterns that support satiety and steady energy rather than fighting your biology by willpower alone.

Is the carbohydrate-preference FGF21 variant unhealthy?

No. The rs838133 A allele is common and is not a disease marker. It has been linked to higher carbohydrate intake but also, in some studies, to lower body-fat percentage. It is one input into your metabolism, best interpreted alongside other genes and your overall lifestyle.

Curious how your own metabolic and appetite pathways are wired? The Precision Peptide Genetic Test analyzes FGF21 and dozens of related variants so you can understand your biology before making diet or wellness decisions with your provider.

The Precision Peptide Genetic Test analyzes how your genes influence peptide-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use. Consult a qualified healthcare provider before beginning any peptide protocol.

This article is part of the PlexusDx Education Hub. Browse all Diet & Genetics education

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.