Markers / Condition
Which genes affect body weight?
The honest headline: the largest common genetic effect on body weight that exists is worth about three pounds. Carriers respond to diet and exercise exactly as well as everyone else, which trials have tested directly. Anyone selling you a genetic diet is selling you something the evidence does not support.
The markers
FTO, the body weight variant
rs1421085 · FTO
The best-known common variant affecting body weight. This particular position is the one shown experimentally to be the cause rather than merely a marker: it disrupts a control site so that developing fat cells switch towards storing energy instead of burning it.
Two copies: Two higher-weight copies, about three pounds on average
MC4R, appetite regulation
rs17782313 · near MC4R
MC4R sits at the centre of the brain circuit that decides when you feel full. Rare severe mutations in it cause childhood obesity; this common variant nearby nudges appetite in the same direction, far more gently.
Two copies: Two copies of the higher-appetite version
Brown fat, the tissue that burns calories as heat
rs1800592 · UCP1
Brown fat does something unique: it uncouples the process that normally makes energy and releases the result as heat instead. It is how a baby stays warm, it is far more active in people who spend time in the cold, and UCP1 is the protein that does the uncoupling.
Two copies: You have the lower-activity version on both copies
Fast-twitch muscle protein
rs1815739 · ACTN3
ACTN3 makes a structural protein found only in fast-twitch muscle fibres. Roughly a fifth of people carry two broken copies and make none of it at all, with no ill effect whatsoever.
Two copies: No working copies
Which versions do you carry?
All of these are readable from an ordinary home DNA test file, in your browser, without uploading it anywhere.
Read my fileCommon questions
Which genes affect body weight?
The honest headline: the largest common genetic effect on body weight that exists is worth about three pounds. Carriers respond to diet and exercise exactly as well as everyone else, which trials have tested directly. Anyone selling you a genetic diet is selling you something the evidence does not support. The markers most often cited are rs1421085 in FTO, rs17782313 in near MC4R, rs1800592 in UCP1, rs1815739 in ACTN3.
What does rs1421085 do?
The best-known common variant affecting body weight. This particular position is the one shown experimentally to be the cause rather than merely a marker: it disrupts a control site so that developing fat cells switch towards storing energy instead of burning it. Carrying two copies: two higher-weight copies, about three pounds on average.
What does rs17782313 do?
MC4R sits at the centre of the brain circuit that decides when you feel full. Rare severe mutations in it cause childhood obesity; this common variant nearby nudges appetite in the same direction, far more gently. Carrying two copies: two copies of the higher-appetite version.
What does rs1800592 do?
Brown fat does something unique: it uncouples the process that normally makes energy and releases the result as heat instead. It is how a baby stays warm, it is far more active in people who spend time in the cold, and UCP1 is the protein that does the uncoupling. Carrying two copies: you have the lower-activity version on both copies.
What does rs1815739 do?
ACTN3 makes a structural protein found only in fast-twitch muscle fibres. Roughly a fifth of people carry two broken copies and make none of it at all, with no ill effect whatsoever. Carrying two copies: no working copies.
Reference information, not medical advice and not a diagnosis. See the medical disclaimer.