Vegetarian diet

In large observational studies, vegetarians get different diseases rather than simply living longer: less heart disease and cancer but more strokes, and the lower death rate seen in some cohorts fades with age. An eating pattern heavy in refined grains, juice and sweets is linked to higher mortality even when it is plant-based.

If you go vegetarian or vegan, build it on whole plant foods — legumes, whole grains, vegetables, fruit, nuts — not refined grains, juice and sweets. Don't expect a large lifespan gain; expect a trade-off.

What it is

A vegetarian diet leaves out meat; some versions keep fish (pesco-vegetarian), and a vegan diet leaves out all animal foods. All the evidence below is observational: it compares people who chose these diets with people who didn't, and the two groups differ in many other ways.

The Adventist evidence: an advantage that fades with age

A large study of Seventh-day Adventists in North America first found vegetarians had 12% lower mortality than meat-eaters, with fish-eating vegetarians doing best.^[1]

The same cohort's 2024 update, with 88,400 people, 12,515 deaths and a median of 11 years' follow-up, suggested — in early, single-cohort evidence — that the advantage depends on age: about 11% lower mortality at 65, but gone by 85. It was clearest in men, though the difference between the sexes was not statistically certain. In late old age the update also found vegetarians more likely to die of stroke (17% higher) and of dementia (13% higher, a borderline result).^[2] The wider Adventist story is on Blue Zones.

British cohorts: no difference overall, a trade underneath

Two British cohorts of 60,310 people and 5,294 deaths found essentially no difference in overall mortality between vegetarians and regular meat-eaters.^[3]

That flat result hides a trade:

Less cancer. Pooled across studies, vegetarians had 13% less cancer and vegans 23% less.^[4]
Less heart disease, more strokes. Over 18 years, British vegetarians had 22% less coronary heart disease but 20% more strokes — about 3 extra strokes per 1,000 people over 10 years, mostly bleeding (haemorrhagic) strokes.^[5]

The kind of plant food decides it

"Plant-based" covers very different diets. A healthful plant-based diet — whole grains, legumes, fruit, vegetables, nuts — is linked to lower mortality. An unhealthful one built on refined grains, fruit juice, sugary drinks and sweets is linked to higher mortality, though both are technically plant-based.^[6] Swapping meat for cola and biscuits is not a longevity strategy.

Plant quality is a floor to clear, not what makes a diet the best: when eight healthy eating patterns were scored in the same 105,015 people, the healthful plant-based score ranked last for healthy ageing, though it still helped.^[7]

Who should be careful

The stroke signal. Both the British and the Adventist cohorts found more strokes or stroke deaths in vegetarians; in the British cohort the excess was about 3 strokes per 1,000 people over 10 years.
Iron and vitamin B12. Plant-forward diets may need attention to both.
Older adults. The stroke and dementia death signals appeared in late old age, and past 70 a plant-forward plate needs a deliberate protein target — see Protein, which sets 1.0–1.5 g/kg a day past 65, spread as about 0.4 g/kg per meal (25–30 g at 65–75 kg, 30–40 g if heavier).

What to do

Make it whole-food. Legumes as the default protein, whole grains, vegetables, fruit and nuts — not refined starch and sugar.
Consider keeping fish. Fish-eating vegetarians did best in the Adventist cohort.
Don't go vegetarian for lifespan alone. The evidence supports a trade-off, not a free win. How it fits among the named diets is on Dietary patterns.