The Adventist Health Studies

The Adventist Health Studies are a series of long-running cohort studies run out of Loma Linda University, tracking members of the Seventh-day Adventist Church, whose religious teaching favors a largely vegetarian diet, discourages tobacco and alcohol, and emphasizes rest and physical activity. The first study, AHS-1, began in 1974; the current phase, AHS-2, enrolled roughly 96,000 participants across North America starting in 2002 and has followed them for years since, recording diet, lifestyle and health outcomes at a scale few voluntary religious populations offer.

The appeal to researchers is that Adventists provide a large population sharing one faith but a wide range of actual dietary practice within it, from strict vegans to regular meat eaters, all living in the same countries and subject to the same medical systems. That internal variation lets the studies compare health outcomes by diet without also having to control for the much larger differences between entirely different national populations, which is a harder comparison to draw cleanly.

Published findings from AHS-2, including the widely cited 2013 analysis of vegetarian dietary patterns and mortality led by Michael Orlich and colleagues, associate vegetarian and vegan diets within the Adventist cohort with lower all-cause mortality and lower rates of several conditions including type 2 diabetes and some cancers, compared to the meat-eating members of the same faith community. Loma Linda, California, where the studies are centered, has since been named one of the world's "Blue Zones," regions researchers have identified as having unusually high concentrations of long-lived residents.

The Adventist studies are epidemiological, not experimental: they observe an existing population rather than assigning diets at random, so the associations they report cannot rule out other shared factors, such as the church's broader lifestyle teaching on rest and community, contributing to the outcomes alongside diet itself. Researchers in the field treat that as a standing limitation of cohort work generally, not a flaw specific to this series.