A Mediterranean diet score written in the blood tracked with lower mortality — but it is not a shortcut test

Food questionnaires are useful, but they ask people to remember a lot: what was on a plate, how often, how much and how it was prepared. A new analysis in The American Journal of Clinical Nutrition asked a different question. Could a pattern of small molecules in blood offer another way to capture how closely someone's eating and metabolism resemble a Mediterranean-style diet?

The researchers used a previously developed signature made from 67 blood metabolites, selected from 302 measured compounds. It is not a test for whether someone had olive oil at lunch. Rather, it is a combined pattern that tended to be higher in people whose diets more closely matched the familiar Mediterranean mix of olive oil, vegetables, fruit, legumes, nuts and fish. The key distinction matters: metabolites reflect both food exposure and the way an individual body processes it.

Their first analysis came from PREDIMED, a Spanish nutrition trial that enrolled adults at high cardiovascular risk but without cardiovascular disease at the start. Of 7,447 trial volunteers, 1,880 had the baseline blood measurements needed for this analysis and 1,648 had a second measure after one year. The median follow-up was about 13 years. Compared with people in the lowest third of the blood-signature score, those in the highest third had a 23% lower relative hazard of death from any cause after the researchers' adjustments.

That pattern did not rest on one cohort. The team also tested it in 12,704 participants from the Nurses' Health Studies and the Health Professionals Follow-up Study in the United States, followed for roughly 25 years on average. Here too, the highest fifth of the signature score was associated with a 23% lower relative hazard of death than the lowest fifth. Across both settings, a one-standard-deviation higher score was linked with a lower rate of all-cause mortality; in the Spanish group, the one-year score was also associated with lower cardiovascular mortality.

The interesting part is not that blood can replace eating well. It cannot. A single score cannot tell a person which food to add, whether they need treatment, or what will happen to them. The authors did not find a statistically significant association with cancer mortality after full adjustment, and changes in the score over the first year were not significantly associated with later mortality. The study is also observational for the score-outcome question, even though PREDIMED itself was a trial, so it cannot prove that raising this number causes a longer life.

Still, the work offers a useful research direction. Self-reported diet and biology do not always agree, and a blood signature may capture a longer-running pattern that a questionnaire misses. For everyday eating, the study supports the less dramatic message rather than a new diet hack: build meals around plants, legumes, nuts, fish where it suits you, and unsaturated fats such as olive oil — then adapt the details to your culture, budget, health needs and advice from your clinician.