Cutting out meat did not translate into a longer life in a large group of middle-aged and older Americans. After an average of 18 years of follow-up, people who called themselves vegetarian, pescatarian or vegan were no more and no less likely to have died than people who ate everything.
The analysis was carried out by Keeley Blackie, Gerd Bobe and Yumie Takata of Oregon State University. It was published on November 23, 2023 as a brief report in the Journal of Health, Population and Nutrition.
A cancer screening cohort, repurposed
The data came from the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial, which enrolled 154,952 Americans aged 55 to 74 between 1993 and 2001. From 1998, participants filled in a food questionnaire that asked whether they followed a vegetarian diet and which foods they excluded entirely.
The researchers analysed 117,673 people who answered those questions. Almost all of them, 116,894 or 99.3%, were omnivores. There were 329 lacto- or ovo-vegetarians, 310 pescatarians who ate fish but no meat, and 140 vegans. Deaths were tracked through yearly questionnaires and the National Death Index up to the end of 2018.
Over that period 39,763 participants died: 39,547 omnivores, 88 lacto- or ovo-vegetarians, 67 pescatarians and 61 vegans.
The fish eaters’ edge disappeared after adjustment
With only age, sex, study centre and trial arm taken into account, pescatarians looked better off, with a 33% lower risk of death than omnivores (hazard ratio 0.67). That advantage shrank and lost statistical significance once the team also adjusted for smoking, alcohol, race, education, body weight and existing illness.
In the fully adjusted model, compared with omnivores, the hazard ratio was 0.81 for pescatarians, 0.99 for lacto- or ovo-vegetarians and 1.27 for vegans. None of these differences was statistically significant. Grouping vegetarians and vegans together against all meat and fish eaters gave a hazard ratio of 1.09, again with no significant difference. Dropping the first two years of follow-up did not change the pattern.
The diet groups differed in other ways. Omnivores were more likely to smoke and drink and less likely to have a college degree, and they had the highest average BMI at 27.2. The vegans, however, had a BMI close to the omnivores’ at 26.9 and more existing illness than the other vegetarian groups.
Why the vegans may not fit the usual picture
The authors suspect many of the self-identified vegans had recently switched diets because of health problems, which would make them look worse on paper. The questionnaire only covered the previous 12 months, so nobody knows how long anyone had avoided meat.
Other limits are spelled out in the paper. Vegetarians and vegans made up just 0.7% of the sample, so there were too few deaths for cause-specific analysis. Diet status rested on two self-report questions, and physical activity was not measured.
The result fits most earlier studies of vegetarians and overall mortality. The exception is the Seventh-day Adventist cohorts, where vegetarians lived longer, but smoking and drinking were far rarer there: 1.1% current smokers versus 9.3% in this cohort.
Study Details:
- Title: Vegetarian diets and risk of all-cause mortality in a population-based prospective study in the United States
- Authors: Keeley Blackie, Gerd Bobe, Yumie Takata
- Journal: Journal of Health, Population and Nutrition
- Publication Date: November 23, 2023
- DOI: 10.1186/s41043-023-00460-9