rs174546
Turning plant fats into the ones your brain runs on
What this position does
Your brain needs long-chain omega-3 and omega-6 fats. You either eat them ready-made, from fish and organ meat, or you build them from the short ones in plants. FADS1 does the building, and the efficient version swept through farming populations that ate mostly plants. Populations that kept eating fish never needed it, and Greenlandic Inuit carry a different version entirely, adapted the opposite way.
Gut and metabolism. Shaped by what your ancestors ate: plants, or fish and meat. This is one of the variants that differs sharply between human populations, because something in the environment made one version worth having.
What your ancestors ate
Fats, folate and the chemistry of plants. Populations that farmed, that fished, or that herded ended up building different enzymes for the same jobs.
What changed: Farming, the last 12,000 years. Grain, milk, settlement, crowds and the diseases crowds carry. Most of the adaptations a consumer chip can read are younger than this, which is why they still differ so sharply between populations.
Why it spread: well established. The environmental pressure behind this variant is documented and not in serious dispute.
Spiral Staircase, chapter 13: The Thrifty Body Spiral Staircase is written by the same author as this site.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version TT | You have the slower-converting version on both copies Less efficient at building long-chain fats from plant oils, which matters more the less oily fish you eat. |
| One copy CT | You carry one efficient copy Intermediate conversion. The most common result in Europe. |
| Two copies CC | You have the efficient version on both copies Efficient at building long-chain fats from plant sources. This is the version that rose with farming, and it is near-universal in South Asian populations with long vegetarian histories. |
Worth knowing. If you convert slowly and eat little oily fish, that combination is the thing worth acting on, and it is a dietary question rather than a genetic one.
How common each version is
| Ancestry group | C (the effect version) | |
|---|---|---|
| African | 97.8% | |
| American | 41.4% | |
| East Asian | 43.4% | |
| European | 65.3% | |
| South Asian | 86.3% |
1000 Genomes Project phase 3, via Ensembl, retrieved 2026-09-23. These groupings are coarse and flatten a great deal of internal diversity, particularly within Africa. A variant being common somewhere tells you where a piece of your ancestry probably comes from, and nothing else.
How many people carry each result
| Ancestry group | TT | CT | CC |
|---|---|---|---|
| African | 0 / 661 | 29 / 661 | 632 / 661 |
| European | 66 / 503 | 217 / 503 | 220 / 503 |
| East Asian | 183 / 504 | 205 / 504 | 116 / 504 |
| South Asian | 10 / 489 | 114 / 489 | 365 / 489 |
| American | 129 / 347 | 149 / 347 | 69 / 347 |
Counts of people, not modelled frequencies: every one of the 2,504 individuals sequenced by the 1000 Genomes Project phase 3, tallied by the genotype they carry. Deriving these from allele frequencies instead would assume random mating inside each group and undercount the homozygotes.
How to find out which you have
If you have taken a test with 23andMe, AncestryDNA, MyHeritage, Family Tree DNA, TellMeGen or Living DNA, this position is very likely already in the raw data file they gave you. You do not need another test.
One thing to watch if you look it up by hand: testing companies report some positions from one DNA strand and some from the other, and the file does not say which. Read the letters as they appear and you will get the opposite of the truth for some positions. Sequencings resolves that automatically.
Source
Coordinates and allele pair verified against Ensembl GRCh37. Direction of effect verified against VEP protein consequences or 1000 Genomes population frequency. Category: Population adaptation.
Common questions
What is rs174546?
rs174546 is a position in the FADS1 gene on chromosome 11. Your brain needs long-chain omega-3 and omega-6 fats. You either eat them ready-made, from fish and organ meat, or you build them from the short ones in plants. FADS1 does the building, and the efficient version swept through farming populations that ate mostly plants. Populations that kept eating fish never needed it, and Greenlandic Inuit carry a different version entirely, adapted the opposite way.
What does it mean if I have CC at rs174546?
You have the efficient version on both copies. Efficient at building long-chain fats from plant sources. This is the version that rose with farming, and it is near-universal in South Asian populations with long vegetarian histories.
What does it mean if I have TT at rs174546?
You have the slower-converting version on both copies. Less efficient at building long-chain fats from plant oils, which matters more the less oily fish you eat.
How do I find out my rs174546 genotype?
If you have taken a home DNA test, this position is very likely in the raw data file you were given. Sequencings reads that file in your browser without uploading it, and resolves which DNA strand each position was reported from, which is the step most manual lookups get wrong.
This is reference information, not medical advice, and not a diagnosis. See the medical disclaimer. Category: Population adaptation.