Remembering everything you ate last week can be difficult, but your blood may keep its own record: traces of how your body processed those meals.
Scientists have found that a blood signature tied to Mediterranean-style eating is linked to risk of dying years later. In a study involving 14,584 people in Spain and the United States, groups with higher signature scores had a lower risk of death during follow-up.
The research, involving scientists from the University of Navarra, Harvard T.H. Chan School of Public Health, and other institutions, offers a way to study diet without relying only on what people remember eating.
Mediterranean-style eating emphasizes vegetables, fruit, legumes, nuts, fish, and olive oil, while limiting red and processed meat. This pattern has been linked to various health benefits, but measuring how closely someone follows it usually involves dietary questionnaires.
"Questionnaires depend on what people remember and report, so they are prone to misclassification," University of Navarra epidemiologist Estefanía Toledo told ScienceAlert.
As the body processes food, it produces or transforms small molecules called metabolites. These can carry information about both what we eat and how our bodies respond to it.
The researchers examined a pattern of 67 metabolites, mostly lipids (fat-related molecules). Developed in 2020, the signature had previously been associated with Mediterranean diet adherence and cardiovascular disease risk. The new study investigated its relationship with long-term mortality.
Many of those fats echo the diet's staples. In earlier work, some tracked closely with olive oil intake, while others are long-chain fatty acids found in nuts and fish.
The team started with blood samples collected from 1,880 participants upon joining a Spanish dietary trial called PREDIMED. These were older adults who had no cardiovascular disease when they enrolled but were at high risk of developing it.
Over roughly 13 years of follow-up, people in the highest third of signature scores had a 23 percent lower risk of death than those in the lowest third, after accounting for factors including age, smoking, body mass index, and existing health conditions.
The researchers then examined data from 12,704 participants in three long-running US studies, followed for an average of 25 years.
The association appeared again: Participants in the highest fifth of signature scores had a 23 percent lower risk of death than those in the lowest fifth.
In the Spanish group, the association remained largely intact after accounting for self-reported adherence to the Mediterranean diet. Toledo explained that the signature may also capture how each person's body absorbs and handles food.
The authors suggest a blood test like this might eventually help doctors spot the people who stand to gain most from changing how they eat.
The results can't, however, tell someone how many years they have left.
"It indicates differences in risk between groups, not an individual's lifespan," Toledo said.
Although PREDIMED was a randomized dietary trial, this analysis of the blood signature and mortality was observational, comparing people's existing scores with what happened to them later. It cannot establish that raising someone's signature score would extend their life.
Scores measured at the start of the trial and after one year, along with their average, were associated with mortality, while changes in the signature over that first year of intervention were not.
The findings suggest the signature may reflect longer-term eating habits and metabolic health, although it's uncertain whether one year is too short to capture the effects of dietary changes.
Before the approach could become a routine blood test, it would need to be tested in more diverse populations, including people of different ages and health backgrounds.
The US participants were health professionals "who are mostly white and relatively healthy," Toledo told ScienceAlert.
Researchers would also need to show that the signature improves risk prediction beyond established risk factors.
The research has been published in The American Journal of Clinical Nutrition.
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