Fibroblast Growth Factor 21 (FGF21)
Evidence: CNeuroendocrine / Appetite-Energy Balance Signaling
Evidence Snapshot
What this grade covers
Very large human genetic evidence base (Soberg 2017, N=6,514; Chu 2013, discovery N=33,533 + replication N=38,360; Schumann 2016, N>105,000) plus a controlled human fasting-exposure study (Galman 2008, duration-dependent: 10-day fast raised FGF21 ~3-fold, 3-day fast did not). Talukdar 2016's sweet/alcohol-preference mechanism is MOUSE/MONKEY-only and must not be presented as human-proven behavior change. No engineered FGF21 analogue exists in the MitoCore registry to firewall against. No direct native/recombinant FGF21 human administration study exists. Overall page grade: C.
Regulatory Context
Native FGF21 is an endogenous human hormone and is not itself an FDA-approved drug product. No engineered FGF21 analogue drug currently exists in the MitoCore registry.
In Plain English
A quick, research-focused overview. It does not replace, and cannot outrank, the detailed evidence below.
What is it?
A liver-derived metabolic-regulator hormone that signals via FGFR1c and its co-receptor beta-Klotho.
Why are researchers interested in it?
Studied for its role in fasting physiology and its genetic links to macronutrient, sugar, and alcohol preference in large human cohorts.
What does the evidence look like?
Very large human genetic evidence base plus a controlled human fasting-exposure study; no direct human administration study.
Biggest things to know
A 10-day fast (but not a 3-day fast) raises human FGF21 about 3-fold; FGF21-pathway gene variants are associated with sugar and alcohol consumption in cohorts of thousands to over 100,000 people.
What don't we know yet?
Whether giving FGF21 to people would reduce sugar or alcohol intake -- that effect is shown only in mice and monkeys.
Research Takeaway
Human and mouse FGF21 cDNA were identified and characterized; FGF21 is preferentially expressed in the liver.
Evidence boundary: Identity/discovery only.
See all 5 evidence claims →Quick Summary
FGF21 is a liver-made hormone involved in fasting physiology and metabolic signaling. Large human genetic studies link the FGF21 pathway to sugar and alcohol intake, while direct behavioral effects of giving FGF21 have only been shown in mice and monkeys.
Mechanism & Research Overview
FGF21 is a liver-made hormone involved in fasting physiology and metabolic signaling. Large human genetic studies link the FGF21 pathway to sugar and alcohol intake, while direct behavioral effects of giving FGF21 have only been shown in mice and monkeys.
Evidence Claims
Individual scientific statements drawn from the sources cited below, each shown with the specific evidence boundary that statement does not establish.
Supported
Human and mouse FGF21 cDNA were identified and characterized; FGF21 is preferentially expressed in the liver.
Does not establish
Evidence boundary: Identity/discovery only.
Sources: Identification of a novel FGF, FGF-21, preferentially expressed in the liver
Supported
A 10-day fast raised plasma FGF21 roughly 3-fold in normal-to-slightly-overweight subjects; a 3-day fast did NOT significantly change plasma FGF21 in healthy lean subjects -- the response is duration-dependent.
Does not establish
Evidence boundary: Must always carry the duration-dependence qualifier; must not be stated as "fasting raises FGF21" without the 3-day-vs-10-day distinction.
Supported
FGF21 administration reduces sweet and alcohol preference in mice and sweet preference in cynomolgus monkeys, via a mechanism requiring the co-receptor beta-Klotho in the central nervous system.
Does not establish
Evidence boundary: Must never be presented as demonstrated human behavior change -- this is an animal administration study.
Supported
In a Danish cohort of 6,514 people, an FGF21-locus genetic variant (rs838133) was associated with increased candy/sugar consumption, with nominal associations to alcohol intake and smoking.
Does not establish
Evidence boundary: Genetic association only; not a demonstration that administering FGF21 changes human sugar intake.
Sources: FGF21 Is a Sugar-Induced Hormone Associated with Sweet Intake and Preference in Humans
Supported
Genome-wide association studies link the FGF21 locus to macronutrient intake (carbohydrate/protein, N=33,533 discovery + N=38,360 replication) and link the FGF21 co-receptor gene KLB to alcohol consumption (N>105,000).
Does not establish
Evidence boundary: Genetic association only; the KLB paper's own mechanistic brain follow-up is mouse and is not part of this claim.
Sources: Novel locus including FGF21 is associated with dietary macronutrient intake; KLB is associated with alcohol drinking, and its gene product beta-Klotho is necessary for FGF21 regulation of alcohol preference
Safety & Evidence Limitations
Considerations reported in the sources cited on this page — not a complete list of every possible risk, and not medical advice.
Safety Consideration
FGF21's sweet/alcohol-preference-reducing effect is demonstrated in mice and monkeys via administration; no human FGF21 administration study exists, so this must not be presented as a proven human behavioral effect.Safety Consideration
A 3-day fast did not raise FGF21 in the frozen source; only a 10-day fast did. A generic 'fasting raises FGF21' statement without this qualifier would misstate the evidence.Safety Consideration
Large human genetic associations (sugar/alcohol/macronutrient intake) are population-level statistical associations with FGF21-pathway variants, not evidence that administering FGF21 changes an individual's intake or behavior.
Research Areas Being Studied
Research areas discussed on this page reflect the Neuroendocrine / Appetite-Energy Balance Signaling category and the sources cited below.
Findings Reported in Studies
Educational summary only — reported in cited studies, not a claim of proven benefit.
- FGF21 Is a Sugar-Induced Hormone Associated with Sweet Intake and Preference in Humans (2017):
- KLB is associated with alcohol drinking, and its gene product beta-Klotho is necessary for FGF21 regulation of alcohol preference (2016):
- Novel locus including FGF21 is associated with dietary macronutrient intake (2013):
- The circulating metabolic regulator FGF21 is induced by prolonged fasting and PPARalpha activation in man (2008):
Study Tables by Evidence Type
Human Studies & Clinical Data
| Title | Year | Population / Model | Dose / Duration / Finding | Safety Notes | Source |
|---|---|---|---|---|---|
| FGF21 Is a Sugar-Induced Hormone Associated with Sweet Intake and Preference in Humans | 2017 | Danish Inter99 cohort, N=6,514 | FGF21-locus variant rs838133 associated with increased candy/sugar consumption, with nominal associations to alcohol intake and daily smoking, in a Danish cohort of 6,514 people. | ||
| KLB is associated with alcohol drinking, and its gene product beta-Klotho is necessary for FGF21 regulation of alcohol preference | 2016 | >105,000 individuals of European ancestry (GWAS + replication); mouse follow-up | GWAS identifies beta-Klotho (KLB), the FGF21 co-receptor gene, as associated with alcohol consumption (rs11940694, P=9.2x10^-12) in humans. | ||
| Novel locus including FGF21 is associated with dietary macronutrient intake | 2013 | Discovery cohort N=33,533; replication N=38,360 | Genome-wide meta-analysis: rs838133 at the FGF21 locus genome-wide significantly associated with carbohydrate/protein intake (P=7.9x10^-9 combined). | ||
| The circulating metabolic regulator FGF21 is induced by prolonged fasting and PPARalpha activation in man | 2008 | Normal-to-slightly-overweight subjects; separate rheumatoid arthritis cohort | A 10-day fast raised plasma FGF21 ~3-fold in normal-to-slightly-overweight subjects; a 3-day fast did NOT significantly change plasma FGF21 in healthy lean subjects -- the response is duration-dependent. |
Animal / Cell / Preclinical Data
| Title | Year | Population / Model | Dose / Duration / Finding | Safety Notes | Source |
|---|---|---|---|---|---|
| FGF21 Regulates Sweet and Alcohol Preference | 2016 | Mice; cynomolgus monkeys | FGF21 administration reduces sweet and alcohol preference in mice and sweet preference in cynomolgus monkeys, via a mechanism requiring the co-receptor beta-Klotho in the central nervous system. | ||
| Identification of a novel FGF, FGF-21, preferentially expressed in the liver | 2000 | Human and mouse cDNA | Human and mouse FGF21 cDNA identified and characterized; FGF21 is preferentially expressed in the liver. |
Regulatory Documents & Official Trial Registries
No Regulatory Documents & Official Trial Registries Listed Yet
This section will be updated as sources are added.
Anecdotal Reported Patterns — Not Medical Advice
Anecdotal Reported Patterns — Not Medical Advice
Reported dosing patterns are included for educational context only. They are self-reported, unverified, not medical advice, and not instructions for human use. Community-submitted patterns are not yet available in this Phase 1 prototype; this section is a placeholder reserved for moderated, aggregated community data.
Lab Markers to Discuss With a Clinician
Educational topics only — not self-monitoring instructions.
FAQ
Disclaimer
Human evidence is strongest for genetic associations and fasting physiology; no study has given native FGF21 to people.
Educational use only. This content is provided for informational and research-summary purposes only. It is not medical advice, not a treatment recommendation, not a dosing guide, and not a substitute for care from a licensed medical professional. Nothing here is intended to diagnose, treat, cure, prevent, or mitigate disease. Reported dosing patterns, when shown elsewhere on the site, must be labeled either as Study / Trial Dosing or Anecdotal Reported Patterns — Not Medical Advice. Community reports are self-reported, unverified, and not scientific proof.
Community-reported experiences, once enabled, must be displayed only as moderated, anonymized, or aggregated data. They are anecdotal, self-reported, unverified, and should never be presented as proof of safety, efficacy, or expected results.
Content status: Published. Last updated 2026-08-28.
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