Abstract
Background: Since meat products represent a major source of protein in the Western diet, findings on whether meat intake significantly contributes to the burden of fatal disease have important clinical and public health implications. Objective: The objective was to examine whether a very low meat intake (less than weekly) contributes to greater longevity. Design: We reviewed data from 6 prospective cohort studies and report new findings on the life expectancy of long-term vegetarians from the Adventist Health Study. Results: Our review of the 6 studies found the following trends: 1) a very low meat intake was associated with a significant decrease in risk of death in 4 studies, a nonsignificant decrease in risk of death in the fifth study, and virtually no association in the sixth study; 2) 2 of the studies in which a low meat intake significantly decreased mortality risk also indicated that a longer duration (≥2 decades) of adherence to this diet contributed to a significant decrease in mortality risk and a significant 3.6-y (95% CI: 1.4, 5.8 y) increase in life expectancy; and 3) the protective effect of a very low meat intake seems to attenuate after the ninth decade. Some of the variation in the survival advantage in vegetarians may have been due to marked differences between studies in adjustment for confounders, the definition of vegetarian, measurement error, age distribution, the healthy volunteer effect, and intake of specific plant foods by the vegetarians. Conclusion: Current prospective cohort data from adults in North America and Europe raise the possibility that a lifestyle pattern that includes a very low meat intake is associated with greater longevity. Am J Clin Nutr 2003;78(suppl):526S-32S.
Generated Summary
This study, published in the American Journal of Clinical Nutrition, examines the relationship between low meat consumption and life expectancy. It reviews data from six prospective cohort studies, and it also includes new findings on the life expectancy of long-term vegetarians from the Adventist Health Study. The research aims to determine whether a very low meat intake (less than weekly) contributes to greater longevity. The methodology involves analyzing existing cohort data, focusing on the impact of low meat intake on mortality risk and life expectancy. The study population includes adults from North America and Europe, with a particular focus on vegetarian cohorts.
Key Findings & Statistics
- A very low meat intake was associated with a significant decrease in the risk of death in four studies, a nonsignificant decrease in the fifth, and virtually no association in the sixth study.
- Two studies showed that a low meat intake significantly decreased mortality risk and also indicated that a longer duration (≥2 decades) of adherence to this diet contributed to a significant decrease in mortality risk and a significant 3.6-y (95% CI: 1.4, 5.8 y) increase in life expectancy.
- In the Oxford Vegetarian Study, a significant 25% decrease in risk for zero meat intake was reported at 12 years of follow-up, but the mortality ratio attenuated after an additional 10 years of follow-up.
- In the German vegetarians study, the age-adjusted mortality ratio was 0.69 (0.49, 0.98) and the multivariate mortality ratio was 0.71 (0.49, 1.02).
- In the Adventist vegetarians study, the age-adjusted mortality ratio was 0.64 (0.48, 0.85) and the multivariate mortality ratio was 0.70 (0.51, 0.96).
- The Health Food Shoppers Study reported no strong association for a “vegetarian” status variable that did not specifically measure meat intake.
- In the Adventist Mortality Study, the hazard ratio for very low meat intake compared to high meat intake was 0.88 (0.82, 0.93).
- In the Adventist Health Study, the hazard ratio for very low meat intake compared to high meat intake was 0.85 (0.76, 0.94).
- In the Italian study, the hazard ratio for meat eaten less than once per week was 0.55 (0.28, 1.10).
- The study notes that for German vegetarians, a 2-fold decrease in mortality risk was adjusted only for age, which may be interpreted with caution.
- The survival plots and data indicate that long-term vegetarians (estimated life expectancy = 86.5 y) experience a significant 3.6-y (95% CI: 1.4, 5.8, from model) survival advantage over short-term vegetarians (estimated life expectancy = 82.9).
Other Important Findings
- The study highlights historical accounts of populations with purportedly greater longevity due to low meat consumption, such as the Hunzakuts and the Vilcabambas.
- It points out the importance of prospective cohort studies in determining the relationship between meat intake and mortality risk.
- The protective effect of a very low meat intake seems to attenuate after the ninth decade.
- The study emphasizes that the benefits of a vegetarian diet may be linked to the specific plant foods consumed.
- The research considered the role of various confounding factors, such as smoking, alcohol use, and chronic diseases, and adjusted for them in some analyses.
- The study notes the potential for measurement error in dietary assessment to bias the effect estimates.
Limitations Noted in the Document
- The study acknowledges the difficulty in accurately determining the attained age in rural areas and interpreting causal effects from ecological data.
- Variations in study methodologies, such as defining and selecting vegetarians, may contribute to differences in mortality ratios.
- The study acknowledges that some of the studies showing strong protective effects (ie, Adventist Studies) compared vegetarians who consumed no meat to nonvegetarians who were weekly meat eaters.
- The study mentions the challenges in interpreting results from observational data due to the potential influence of confounding factors.
- The researchers note that a “healthy volunteer” bias, where health-conscious individuals participate in studies, could affect the difference in survival between vegetarians and non-vegetarians.
- Measurement error in dietary assessment may bias the effect estimate toward the null, potentially understating the protective associations.
Conclusion
The study’s findings suggest that a lifestyle pattern involving very low meat intake is associated with greater longevity, supporting the possibility that reduced meat consumption contributes to improved health outcomes. The research emphasizes the importance of long-term adherence to a vegetarian diet, suggesting that sustained dietary patterns may further reduce mortality risk. The study’s authors emphasize the need for further investigation into the roles of specific plant foods in promoting longevity among vegetarians. It highlights the potential for significant increases in life expectancy associated with long-term adherence to a vegetarian diet. The study’s findings contribute to the ongoing discourse on diet and health, suggesting the need for a more nuanced understanding of the impacts of meat consumption and plant-based diets. The researchers point out the need for future investigations into the causative roles of specific plant foods and the limitations of observational studies. In summary, the study’s conclusions point to the potential health benefits of lower meat intake and the need for continued research to fully understand its impact on human longevity.