Study analysis · American Journal of Epidemiology · 2017
Yogurt and cheese could save your life—but milk might not help at all.
People who ate more yogurt and cheese lived longer, especially if they weren't overweight, but drinking milk didn't make any difference.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study watched what people ate for 11 years and noticed that those who ate more yogurt and cheese tended to live longer. But it didn’t make them eat more—it just watched. So we can’t say yogurt and cheese made them live longer, just that they were linked.
What’s the bottom line?
Scientists tracked what 42,000 people in Iran ate for 11 years to see if dairy foods like yogurt and cheese affected how long they lived.
How strong is this study?
This study is pretty strong because it followed tens of thousands of people for a long time and asked them lots of questions about their lives. But since people chose what they ate on their own, we can’t be 100% sure it was the food that helped—not other things like how much they exercised or how much stress they had.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
38 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=42403)+20/20
- Follow-up+10/10
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervals+15/15
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 560 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
This design cannot establish causation — the findings describe an association, not a cause. This is an observational cohort study with no randomization or intervention. While it adjusts for many confounders, it cannot rule out residual confounding or reverse causation, so it cannot establish cause-effect relationships.
No Conflicts
No conflicts of interest identified
No conflicts of interest were disclosed, and the study was funded by independent academic and public health institutions with no evidence of industry influence.
Funders
Conflict Details
Harvard T.H. Chan School of Public Health: Author affiliated with institution that received funding
US National Cancer Institute: Author affiliated with institution that received funding
US National Cancer Institute: Author affiliated with institution that received funding
International Agency for Research on Cancer: Author affiliated with institution that received funding
International Agency for Research on Cancer: Author affiliated with institution that received funding
+2 more conflicts
Independent Analysis Safeguards
- Analysis conducted using STATA by authors at academic institutions
- Statistical models adjusted for multiple confounders
- Data reviewed by multiple institutions with independent IRB approvals
The study was conducted by academic institutions with no industry funding. All authors are affiliated with universities or public research organizations. No industry ties, employment, or financial relationships with commercial entities were disclosed. The funding sources are all non-industry and public health entities.
Key takeaways
- 01
People who ate more yogurt and cheese were 16–26% less likely to die from heart disease, and 11–16% less likely to die from any cause.
- 02
People who ate milk or high-fat dairy didn't show any benefit.
- 03
The benefit only happened in people who weren't obese.
- 04
Yes — eating yogurt and cheese regularly may help people live longer, especially if they're not overweight, but milk and butter don't seem to help or hurt.
Surprising findings
- Cheese was linked to a 26% lower risk of cardiovascular death—more than yogurt or any other dairy.Most people assume yogurt is the 'healthy' fermented dairy, but cheese—often seen as indulgent—had the strongest protective effect in this study.
- Milk consumption showed no benefit—even in people who drank it regularly.Global health guidelines often promote milk for calcium and bone health, but this massive study found zero mortality benefit, contradicting prior Western studies.
- The protective effect of dairy vanished in obese individuals.Most nutrition studies assume benefits are universal, but here, obesity completely negated the advantage—suggesting metabolic health may be the real gatekeeper.
Practical takeaways
Swap one serving of milk or butter daily for yogurt or cheese—especially if you're not obese.
This study was done in Iran, where dairy is minimally processed and unfortified. Results may not directly apply to fortified or ultra-processed dairy in Western diets.
medium confidenceIf you're overweight or obese, focus on weight loss first—dairy alone won't reduce your mortality risk if your BMI is 30+.
The study didn't test weight loss interventions—so we don't know if losing weight restores dairy's benefits.
low confidenceDon't feel guilty about full-fat cheese—it didn't increase risk in this study.
This doesn't mean you should eat unlimited cheese. Portion control and overall diet quality still matter.
medium confidenceWhy this study matters
Fermented Dairy = Longevity Boost
Those who ate the most yogurt and cheese had up to a 26% lower risk of dying from heart disease and 16% lower risk of dying from any cause, according to a 11-year study of 42,403 Iranians. The effect was strongest for low-fat versions, which made up 97% of cheese and 89% of yogurt consumed.
This flips the script on the 'all dairy is bad' myth—fermented dairy like yogurt and cheese may be uniquely protective, even in populations with low overall dairy intake.
Obesity Blocks Dairy's Benefits
The mortality-reducing effects of dairy disappeared entirely in people with a BMI of 30 or higher. Non-obese individuals saw a 22% lower risk of death from any cause with high dairy intake, but obese participants saw no benefit at all.
It’s not just what you eat—it’s who you are. This suggests obesity may interfere with the biological mechanisms that make dairy protective.
Milk Is a Non-Factor
Despite being the most commonly consumed dairy product globally, milk showed zero association with reduced risk of death from heart disease, cancer, or any cause—even at moderate intake levels up to 0.6 servings per day.
This contradicts decades of public health messaging that equate milk with health. In Iran, where most milk is high-fat and unfortified, it simply didn’t move the needle.
High-Fat Dairy Isn't the Villain
Contrary to popular belief, high-fat dairy like butter and full-fat milk showed no increased risk of death—even though they’re packed with saturated fat. The study found HR=1.01 for all-cause mortality.
This challenges the long-standing dogma that saturated fat = heart disease death. Food matrix and fermentation may matter more than fat content alone.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Standing
Who’s using this study?
The videos and claims on this site that lean on this study, and the researchers who wrote it.
1 video from Physionic cite this study, drawing 6 claims from it.
- Contradicted
Evidence contradicts this claim.
Evidence - Correlational evidence
The evidence shows a real association, but the studies are observational, so they cannot prove cause and effect. Stronger studies could still change the picture.
Evidence - Conflicting evidence
Evidence points in both directions — no clear conclusion yet.
Evidence - Very strong evidence
Randomized or controlled trials support this claim, alongside consistent supporting evidence.
Evidence - Very strong evidence
Randomized or controlled trials support this claim, alongside consistent supporting evidence.
Evidence - Conflicting evidence
Evidence points in both directions — no clear conclusion yet.
Evidence