GSTM1: the detox gene about half of us are missing
Unlike a normal SNP, GSTM1 is present or missing — a whole-gene deletion. That makes it interesting, and it makes it hard for a consumer DNA file to read.
GSTM1 makes a glutathione S-transferase — a phase-two detox enzyme that tags certain compounds with glutathione so your body can clear them. What makes GSTM1 unusual is how it varies: instead of a single-letter change, the whole gene is deleted in a large share of people. If you inherited a deletion from both parents you are GSTM1-null and make none of this particular enzyme. Roughly half of people are, though the exact frequency varies by ancestry. It is normal human variation, not a disorder, and other closely related enzymes cover much of the same work.
What GSTM1 does
GSTM1 helps process a long list of everyday compounds, including the isothiocyanates like sulforaphane that you get from cruciferous vegetables (broccoli, kale, Brussels sprouts, cabbage). Your GSTM1 status measurably changes how you handle those compounds: in a controlled broccoli trial, GSTM1-null people actually cleared sulforaphane metabolites into the urine faster early on and had a higher plasma exposure than GSTM1-positive people. The epidemiology on who gets the most cancer-risk benefit from broccoli is more mixed, and has often pointed the other way, so we won't tell you your deletion is either a superpower or a problem. The honest read is that GSTM1 shifts the processing, not that one version wins.
One important caveat up front: this is a structural deletion, not a tidy A-or-G letter, and consumer DNA files (23andMe, AncestryDNA) do not reliably report it. So unlike the rest of our guides, we can't turn your raw data into a confident GSTM1-null-or-present result. What we can do is give you the biology and a lever that is low-risk no matter which version you carry.
Your variants, decoded
GSTM1 varies by deletion of the entire gene, so the meaningful states are 'functional' (at least one working copy) or 'null' (both copies deleted) — not a genotype like AA/AG/GG.
| Functional (present) | You carry at least one working copy and make the GSTM1 enzyme. |
| Null (both copies deleted) | Roughly half of people, varying by ancestry. You make no GSTM1 enzyme; related glutathione S-transferases handle much of the same job. |
We show genotypes on the forward strand and ignore letter order. Your own export may print the complementary letters. Same result either way.
What the research suggests
Cruciferous vegetables are the practical lever here, and they are a good idea regardless of your GSTM1 status. They supply glucosinolates that become sulforaphane and related isothiocyanates. GSTM1 genotype changes how you metabolise those compounds, and controlled feeding studies show the body's response to cruciferous vegetables differs by GSTM1 genotype — but the vegetables themselves are broadly beneficial and low-risk either way. A sulforaphane or broccoli-sprout-extract supplement is a reasonable option if you rarely eat these foods; the whole vegetable is the better-evidenced starting point.
PubMed 16332662 · Gasper et al., Am J Clin Nutr 2005: in a randomized crossover broccoli trial, GSTM1-null and GSTM1-positive subjects differed measurably in plasma sulforaphane exposure and early urinary excretion. PubMed 21272319 — Brauer et al., Nutr J 2011: cruciferous-vegetable supplementation altered the serum peptidome in a GSTM1-genotype-dependent manner.
Educational only, not medical advice. “General evidence” means the finding is real, but the benefit isn’t specific to your genotype.
See this matched to your own DNA, free.
Upload your 23andMe or AncestryDNA file and you'll get your actual GSTM1 result, plus every other variant worth acting on. Every line cited. Your file is never stored.
Questions
Can I find out if I'm GSTM1-null from my 23andMe or AncestryDNA file?
Not reliably. GSTM1 varies by a whole-gene deletion rather than a single letter, and consumer genotyping chips aren't built to call that copy-number change cleanly from your raw data. Some third-party tools guess using nearby marker SNPs, but the result isn't dependable. A dedicated lab test is the honest way to know your GSTM1 status.
Is being GSTM1-null bad?
No. Roughly half of people are GSTM1-null, and other glutathione S-transferase enzymes carry much of the same load. It changes how you process some compounds; it is not a diagnosis and not something to worry about on its own.
Should I take a sulforaphane supplement if I'm GSTM1-null?
The stronger, simpler move is to eat cruciferous vegetables regularly, which is beneficial across GSTM1 genotypes. A sulforaphane or broccoli-sprout-extract supplement is a reasonable add-on if you rarely eat these foods, but the evidence is clearest for the whole vegetables.