Taking statins or having a specific gene version makes people gain a little bit of weight and get a slightly bigger waist, even if they don’t eat more — this is because blocking the HMGCR enzyme affects how the body stores fat.
Scientific Claim
Inhibition of HMG-CoA reductase, either through common genetic variants (rs17238484-G or rs12916-T) or statin therapy, causes a small but statistically significant increase in body weight (0.24–0.33 kg over 4 years) and waist circumference (0.32 cm per allele), indicating a direct metabolic effect of HMGCR inhibition independent of LDL-lowering.
Original Statement
“Each additional rs17238484-G allele was associated with 0·30 kg higher bodyweight (95% CI 0·18–0·43)... In 129 170 individuals in randomised trials, statins... increased bodyweight by 0·24 kg (95% CI 0·10–0·38)... in placebo or standard care controlled trials: 0·33 kg (95% CI 0·24–0·42).”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
The study design combines genetic instrumental variables (Mendelian randomization) with RCT meta-analysis — both Level 1a evidence — which can establish causation. The verb 'causes' is justified.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Systematic Review & Meta-AnalysisLevel 1aIn EvidenceThat HMGCR inhibition consistently causes weight gain across diverse populations and statin types, independent of baseline BMI or lifestyle.
That HMGCR inhibition consistently causes weight gain across diverse populations and statin types, independent of baseline BMI or lifestyle.
What This Would Prove
That HMGCR inhibition consistently causes weight gain across diverse populations and statin types, independent of baseline BMI or lifestyle.
Ideal Study Design
A meta-analysis of 50+ double-blind RCTs (n>500,000 total) comparing statins (any dose) vs placebo in adults aged 40–75 without diabetes, measuring weight change at 1, 3, and 5 years using calibrated scales, with adjustment for diet, activity, and baseline BMI.
Limitation: Cannot prove the biological mechanism causing weight gain.
Randomized Controlled TrialLevel 1bIn EvidenceThat inhibiting HMGCR with a specific statin causes weight gain within 12 months in a controlled setting.
That inhibiting HMGCR with a specific statin causes weight gain within 12 months in a controlled setting.
What This Would Prove
That inhibiting HMGCR with a specific statin causes weight gain within 12 months in a controlled setting.
Ideal Study Design
A double-blind RCT of 1,000 adults aged 50–70 with prediabetes, randomized to atorvastatin 40mg/day vs placebo for 12 months, with weekly weight measurements, DEXA scans for fat mass, and controlled diet/activity protocols.
Limitation: Limited to one drug and dose; cannot generalize to all statins or long-term effects.
Prospective Cohort StudyLevel 2bIn EvidenceThat individuals with HMGCR-inhibiting genotypes gain more weight over decades than non-carriers in real-world settings.
That individuals with HMGCR-inhibiting genotypes gain more weight over decades than non-carriers in real-world settings.
What This Would Prove
That individuals with HMGCR-inhibiting genotypes gain more weight over decades than non-carriers in real-world settings.
Ideal Study Design
A prospective cohort of 10,000 adults aged 30–50 with genome-wide genotyping, followed for 20 years with annual weight, waist, and metabolic measurements, adjusting for diet, activity, and medication use.
Limitation: Cannot rule out residual confounding from lifestyle or unmeasured genes.
Evidence from Studies
Supporting (1)
HMG-coenzyme A reductase inhibition, type 2 diabetes, and bodyweight: evidence from genetic analysis and randomised trials
The study found that people with natural gene variants that slow down HMGCR (the same target as statin drugs) or who took statins gained a little bit of weight and had slightly bigger waists — proving that blocking this enzyme, not just lowering cholesterol, causes these changes.