Around America's original blue zone, 42% of over-35s said they were vegetarian and 27% of under-36s did. One survey can't say if a generation is leaving

Loma Linda, in Southern California, is the odd one out among the five blue zones, the places known for unusually many people reaching their 90s and beyond. Unlike the others, it has no geographic or cultural isolation to point to. It is a mixed city in a busy part of the state, known for a concentration of Seventh-day Adventists whose church has promoted a meat-free diet since the 1860s. Fast-food outlets and big retail chains were allowed inside the city limits for the first time only around 2013 and 2014, and some of the authors of this new paper say they were part of a coalition that tried to stop them. So they had a question close to home: are younger people here still eating the way the place became famous for?

The answer comes from a questionnaire filled in at health fairs and community events in Loma Linda and nearby parts of San Bernardino and Riverside counties. Of 670 adults recruited, 615 gave usable answers. Just over half (339) were Adventists. People ticked one box for their diet, and because the vegan, lacto-ovo and fish-eating groups were each small, the researchers merged them: 240 people, or 39%, counted as vegetarian. The paper appeared in the American Journal of Lifestyle Medicine on 28 October.

The paper's main comparison is that vegetarians were older, with a mean age of 62.9 against 58.3. Laying out its Table 1 by age group gives a clearer picture, and the arithmetic here is ours: 27% of those aged 18 to 35 were vegetarian (32 of 120), against 42% of those aged 36 to 65 (83 of 198) and 42% of those 66 and over (125 of 297). So there was no steady slope across adult life. Middle-aged and older people looked the same, and the gap sat with the youngest group.

The age gap also belonged almost entirely to the Adventists. Among them, vegetarians averaged 63.3 years and non-vegetarians 54.4. Among everyone else, the two groups were practically the same age, 61.2 and 60.7. The authors read this as a religious and cultural pattern, not a general generational one. Meanwhile 16.3% of the non-Adventists were vegetarian (45 of 276), roughly three times the 6% or so the paper cites for the US as a whole. That may be the local culture rubbing off, as the authors suggest, or it may simply be who turns up at health fairs.

Now the awkward part for anyone wanting a story about decline: the younger group was the leanest. Mean BMI was 25.1 in the 18 to 35s, 26.7 in the middle group and 26.2 in the oldest, and young Adventists were the lowest of all at 24.5. Across the whole sample, vegetarians averaged 24.8 and non-vegetarians 27.0; 60% of vegetarians were in the normal range against 40% of non-vegetarians. These are raw comparisons. The tests didn't adjust for age, sex, income or exercise, and the BMI came from height and weight people wrote down themselves, which tends to flatter. Age muddies it further, since body weight tends to build up across adulthood whatever people eat.

A single survey also can't separate a generation walking away from a tradition from young people who may yet take it up, because nobody was followed over time. The authors say so plainly and call for long-term studies. Recruiting at health fairs with a free health check as the thank-you won't give a fair sample of anyone, the study didn't record who actually lived inside Loma Linda, and diet was one tick box with no check on what people really ate. Read the numbers closely too. The discussion says about two-thirds of Adventists were vegetarian, but the paper's own count is 57.5% (195 of 339). It also gives vegetarian rates of 29.7% for those 50 or younger and 57.5% for those 51 or older, and those can't both fit with 240 vegetarians and Table 1's age groups, so we have relied on the table. The Adventist-only split, 39.2% against 64.8%, does fit. The study had no outside funding and the authors declared no conflicts of interest.