People who said they choose food with the planet in mind ate no closer to the planet-friendly diet than anyone else, in 300 adults at a Turkish diet clinic

In 2019 the EAT-Lancet Commission set out what it called the Planetary Health Diet: mostly vegetables, fruit, whole grains, beans and nuts, modest amounts of fish, eggs and dairy, and very little red meat or added sugar, a way of eating meant to be good for people and lighter on the land, water and climate. Researchers have since turned it into a score, the Planetary Health Diet Index, which runs from 0 to 150 across 16 food groups. A study published in Frontiers in Nutrition on 28 October asked three questions at once about people who score well on it: do they eat better, do their meals leave a smaller footprint, and do they actually care about sustainability when they buy food?

The team, from Bitlis Eren University, recruited 300 adults aged 18 to 64 who came to the diet clinic of a public hospital in Bitlis, eastern Türkiye, between January and July 2025. The clinic is not limited to any one illness, but people with eating disorders, pregnant or breastfeeding women and those on strict medical diets were left out. Each person described everything they had eaten over the previous 24 hours, with a photo catalogue to pin down portion sizes, and was weighed and measured. From that single day the researchers worked out three things: a Planetary Health Diet score, a Healthy Eating Index score (the US Department of Agriculture's 0 to 100 measure of diet quality), and an estimated carbon and water footprint, by multiplying each food by published figures for how much greenhouse gas and water it takes to produce. Everyone also filled in a 16-item questionnaire on how much environmental, ethical, animal-welfare and local or seasonal concerns shape their food choices.

The first answer was yes. People with higher planetary scores also had better diet quality (a correlation of 0.48), and the average Healthy Eating Index rose steadily across the four planetary-score groups, from 32.8 in the lowest quarter to 44.6 in the highest. That sounds encouraging until you see where the scale's lines are: 80 or more is a good diet and 50 or below is poor, so even the best-scoring quarter of this group sat in the poor range.

The footprint answer was much fainter. A higher planetary score did go with a slightly smaller carbon and water footprint, and that held after allowing for age, sex, schooling, weight, exercise, smoking and how much people ate, and again when footprints were counted per 1,000 calories. But the link was weak (a correlation of minus 0.13), the score explained only about 1% of the difference in footprints between people, and when the group was split into quarters by score, the footprints of the four quarters were not meaningfully different.

The third answer was the surprising one. How strongly people said sustainability guides their food choices had no relationship at all with how closely their plate matched the planetary pattern (a correlation of minus 0.01). Concern did vary between groups: women scored a little higher than men, and people with a university or associate degree higher than those who left after middle school. The authors suggest that the questionnaire captures motives and the diet score captures what was eaten, and that the two simply measure different things. Neither the planetary score nor diet quality was linked to BMI, waist size or body fat.

The limits are real. One day of eating is a thin slice of anyone's habits, and because the diet scores and the footprints all came from that same day's list, some of the agreement between them is built in: the two diet indexes reward many of the same foods. The footprint figures were borrowed from international studies rather than Turkish farms, so the authors treat them as a way to compare people, not as true measures of impact. And this was one clinic in one province, among people who had come to see a dietitian. What the study does offer is a rare look at all three sides together, and a reminder that caring about the planet and eating for it are not the same thing.