How much does diet affect life expectancy?
At age 40, the difference between the best and worst answer here is about 3.4 years of life expectancy — 3.5 for men and 3.2 for women. That is the gap between “genuinely excellent” and “mostly fast food”, holding everything else constant.
Diet is where the gap between confident advice and solid evidence is widest. The direction is not seriously disputed — more legumes, whole grains and nuts, less processed and red meat — but the size of the effect rests on modelling rather than on anyone having run the experiment.
What each answer costs, at 40
| Answer | Hazard ratio | Years vs. best |
|---|---|---|
| Genuinely excellent(Mediterranean-ish) | 0.89 | best |
| Mostly whole foods | 0.95 | −0.7 |
| Pretty average | 1.02 | −1.4 |
| Could be better | 1.11 | −2.2 |
| Mostly fast food(beige, fried, delivered) | 1.24 | −3.4 |
Computed from the SSA 2023 period life table with this factor’s hazard ratio applied and every other factor held neutral. Source: Fadnes et al., PLOS Medicine 2022; Schwingshackl et al. 2017.
Does it matter less as you get older?
Yes, and by a lot. A hazard ratio applies to the years you have left, so the same answer costs less in absolute terms the later you are asked it. That is an argument for changing it early, not for concluding it no longer matters.
| If you are now | Men | Women |
|---|---|---|
| 30 years old | 3.8 yrs | 3.4 yrs |
| 40 years old | 3.5 yrs | 3.2 yrs |
| 50 years old | 3.2 yrs | 3.0 yrs |
| 60 years old | 2.8 yrs | 2.7 yrs |
| 70 years old | 2.2 yrs | 2.3 yrs |
What the evidence actually shows
The Food4HealthyLife model, published in PLOS Medicine by Fadnes and colleagues, estimated that a sustained shift from a typical Western diet to an optimised one from age 20 was worth around ten years, falling to about eight years if started at 60 and three and a half at 80. Most of the modelled gain came from the first few substitutions rather than from perfect adherence.
What to do about it
Legumes, whole grains and nuts up; processed and red meat down. Modelling says a sustained shift is worth years, and most of the gain comes from the first few swaps.
Where this number is weak
This is the softest factor in the model. Dietary intake is self-reported, badly, and people who eat well differ from people who do not in a hundred ways no statistical adjustment fully removes. The model deliberately gives diet a narrower range than smoking or weight for exactly this reason.
More generally: these are observational cohorts, which show association rather than proof of cause. The full methodology sets out every simplification the model makes.
What is it costing you?
The calculator weighs this against your other nine factors and ranks them.
Then make it count. The Extension Plan turns your result into a 12-week plan, starting with the habit worth the most years to you · $9. See what is in it →