New US dietary guidelines showed no clear mortality link in 17,855 Spanish adults; a Mediterranean diet did

When the US government published its 2025-2030 Dietary Guidelines for Americans in January, the headline was a change of direction. The official summary site declares an end to what it calls the war on protein, puts protein and vegetables at the base of a new food pyramid, and lists meat, seafood and dairy alongside nuts and olives as sources of healthy fats. What nobody could say was whether eating that way goes with a longer life, because the guidelines were too new to have been tested against death rates.

A team at the University of Navarra in Spain has now run a first test, using a cohort it has followed since 1999. They scored the diets of 17,855 Spanish university graduates, mean age 37, against the new guidelines and against a traditional Mediterranean diet, and counted deaths over a median of 14.3 years. Closely following the US guidelines did not go with clearly fewer deaths. Eating the Mediterranean way did, by about a third. The study, led by Luiz Menezes-Junior of the university’s Department of Preventive Medicine and Public Health, with Maira Bes-Rastrollo as senior author, appeared in Clinical Nutrition in September.

What did the Spanish study compare?

The participants belong to the Seguimiento Universidad de Navarra cohort, known as SUN, which translates as the University of Navarra Follow-up. All were free of chronic disease when they joined, and every two years they answer questionnaires about their health. At the start each filled in a 136-item semi-quantitative food frequency questionnaire, a long checklist of how often they ate each of 136 foods, and the researchers turned those answers into two scores.

The first was a score of adherence to the 2025-2030 DGA, the authors’ abbreviation for the guidelines, built by the team itself and running from 0 to 28 points. The second was the well-established Mediterranean Diet Score, which first appeared in a 2003 Greek study and runs from 0 to 9, with higher scores indicating greater adherence. A person earns a point for each Mediterranean food group, such as vegetables, fruits, legumes, cereals and fish, where their intake was above the median consumption of the group. Another point goes to a high ratio of monounsaturated-to-saturated fatty acids, the balance of olive-oil-type fats to animal fats. Eating less meat and dairy than the median earns a point too, as does moderate wine with meals.

On paper the two eating patterns are not far apart. The government’s summary of the new guidelines says that added sugars are not recommended at all, asks for grains in whole or traditionally prepared forms, with oats, rice and true sourdough preferred, and tells Americans to avoid highly processed food. A Mediterranean diet would pass most of those tests. Where the two part company is in how they treat animal foods. The guidelines name meat and dairy among the sources of healthy fats and put protein at the base of the pyramid, while the Mediterranean score gives a point for eating less meat and dairy than the median person in the study.

Deaths were checked against Spain’s National Death Index, so nobody had to report their own. The researchers then compared people in the top quarter of each score with those in the bottom quarter, allowing for other differences between them.

Did following the new US guidelines go with fewer deaths?

Not clearly. Over the follow-up, 525 deaths occurred among the 17,855 participants, about 3%. Comparing highest to lowest adherence, the guidelines score showed no clear association with death from any cause, from cardiovascular disease or from cancer, meaning no difference large enough to rule out chance.

The numbers explain why “no association” has to be read carefully. For death from any cause, the best estimate was 13% lower risk in the top quarter, but the range of plausible values ran from about a third lower to 13% higher. For cardiovascular deaths the estimate pointed the other way, 62% higher, with a range stretching from slightly lower risk to three times the risk. With so few heart deaths in a young cohort, the study could neither confirm a benefit nor detect harm. The best estimate was smaller than the Mediterranean one, but the range is wide enough that a benefit of similar size cannot be excluded.

One detail softens the null further. The authors report that “specific plant-based DGA components and limiting processed meats showed independent inverse mortality associations,” meaning those parts of the guidelines, taken on their own, did track with lower risk. The guidelines overlap with the Mediterranean pattern in exactly those places. Whether the newer emphases, such as more animal protein and full-fat dairy, pulled the overall score toward the null is a question the study does not answer.

How did the Mediterranean diet compare in the same cohort?

The contrast is the reason the study was designed this way. High MedDiet adherence was inversely associated with death from any cause, from cardiovascular disease and from cancer. People in the top quarter of the Mediterranean score had about a third lower mortality than those in the bottom quarter, roughly 60% lower risk of cardiovascular death and about 40% lower risk of dying of cancer. The cardiovascular figure, like the guidelines figure, rests on few deaths and has a wide range.

That result matches a long line of research. The Greek study that introduced the score found a two-point increment in the Mediterranean-diet score went with a quarter lower death rate among 22,043 adults. A 2008 meta-analysis of eight cohorts covering 514,816 people found that a two point increase in the adherence score went with about 9% lower mortality. In the US Women’s Health Study, which followed 25,315 initially healthy women for an average of 24.7 years, those with the highest scores had lower mortality, although the gap shrank once lifestyle factors were taken into account.

The same Spanish cohort also tells a story about guidelines over time. In 2018 the Navarra group tested the previous edition, the 2015-2020 Dietary Guidelines for Americans, in 16,866 SUN participants and found the top quarter had reduced all-cause, cardiovascular and cancer mortality compared with the bottom; their risk of dying from any cause was about 58% lower. In two large US cohorts, the Nurses’ Health Study and the Health Professionals Follow-up Study, greater adherence to various healthy eating patterns went with lower mortality, including about a fifth lower for the Healthy Eating Index, which measures how closely people follow the older guidelines. In the same cohort, then, a score for the older guidelines tracked with longer life and the score for the new ones did not, although the two scores were built differently and tested in somewhat different groups of participants.

Why should the null for the new dietary guidelines be read cautiously?

Several features of the study limit what it can show. The participants were young when they joined, mean age 37, and highly educated, which is why only about 3% had died 14 years later, and why the estimates have such wide ranges.

Diet was measured once, at the start. People change how they eat over 14 years, and the food questionnaire predates the new guidelines, so the score measures how closely people happened to eat in ways the guidelines now describe, not people deliberately following them. The score itself is the authors’ translation of the guidelines into points, and a different translation, weighting protein or dairy differently, could give a different answer.

This was also an observational study. People who eat a Mediterranean diet in Spain may differ in other ways from those who do not, and adjustment for measured factors cannot remove every difference.

Then there is who ran the comparison. Miguel Ángel Martínez-González, a co-author, leads a research program that has built much of the evidence for the Mediterranean diet. It includes a large Spanish trial known as PREDIMED, which found fewer major cardiovascular events, a combined count of heart attacks, strokes and cardiovascular deaths, among high-risk Spaniards assigned to a Mediterranean diet supplemented with extra-virgin olive oil or nuts. That trial’s original 2013 report was withdrawn after problems with how some participants were randomized, and a corrected analysis was published in 2018 with similar results. The new result may well be right, but a team testing a rival diet against its own long-standing favorite is not an independent referee.

What the result means for the new dietary guidelines

The authors draw a firm conclusion. In their words, “Dietary recommendations should prioritize the MedDiet over the recent DGA 2025-2030 and particularly some features common to both dietary models.” Their own data support a narrower statement: in this cohort, adherence to the new guidelines “does not appear to be associated with reduced mortality,” while the Mediterranean score kept the association it has shown for two decades.

The US guidelines were not written for Spanish graduates, and a single cohort with 525 deaths is a first look, not a verdict. Larger and older populations, including American ones, will be needed to say whether the shift toward animal protein and fats changes anything about survival. How any eating pattern fits a particular person’s health is assessed by their doctor.

For now, the better-tested of the two diets is still the one around the Mediterranean.