Abstract
The Adventist Health Study 2 is a large cohort that is well suited to the study of the relation of vegetarian dietary patterns to health and disease risk. Here we review initial published findings with regard to vegetarian diets and several health outcomes. Vegetarian dietary patterns were associated with lower body mass index, lower prevalence and incidence of diabetes mellitus, lower prevalence of the metabolic syndrome and its component factors, lower prevalence of hypertension, lower all-cause mortality, and in some instances, lower risk of cancer. Findings with regard to factors related to vegetarian diets and bone health are also reviewed. These initial results show important links between vegetarian dietary patterns and improved health. Am J Clin Nutr 2014;100(suppl):353S-8S.
Generated Summary
This is a review article that examines the initial published findings of the Adventist Health Study 2 (AHS-2), a large cohort study designed to investigate the relationship between vegetarian diets and various health outcomes. The study recruited approximately 96,000 participants across the United States and Canada, primarily from Seventh-day Adventist churches. The cohort includes a significant representation of black subjects to address underrepresentation in previous studies. The review focuses on how different vegetarian dietary patterns, defined along a continuum of animal food avoidance (vegan, lacto-ovo-vegetarian, pescovegetarian, semivegetarian, and nonvegetarian), relate to health outcomes like body mass index (BMI), diabetes mellitus, metabolic syndrome, hypertension, bone density, mortality, and cancer. The methodology involves analyzing data from the AHS-2 cohort and reviewing early publications that have examined the connection between vegetarian diets and health.
Key Findings & Statistics
- Dietary Pattern Prevalence: The study categorized participants based on their dietary patterns. The prevalence rates were as follows: vegan (7.7%), lacto-ovo-vegetarian (29.2%), pescovegetarian (9.9%), semivegetarian (5.4%), and nonvegetarian (47.7%).
- BMI Findings: The study found significant differences in BMI across different dietary patterns. Mean BMIs were 23.6 for vegans, 25.7 for lacto-ovo-vegetarians, 26.3 for pescovegetarians, 27.3 for semivegetarians, and 28.8 for nonvegetarians. After adjusting for age, sex, and race, mean BMIs were 24.1 for vegans, 26.1 for lacto-ovo-vegetarians, 26.0 for pescovegetarians, 27.3 for semivegetarians, and 28.3 for nonvegetarians.
- Metabolic Syndrome: The study examined the relationship between dietary patterns and metabolic syndrome. The prevalence rates of metabolic syndrome were 25.2% for vegetarians, 37.6% for semivegetarians, and 39.7% for nonvegetarians. Vegetarians had 0.44 (95% CI: 0.30, 0.64) times the odds of having metabolic syndrome as did nonvegetarians.
- Hypertension: The study found that vegetarians had a lower risk of hypertension compared to nonvegetarians. The adjusted ORs for hypertension were 0.37 (95% CI: 0.19, 0.74) and 0.57 (95% CI: 0.36, 0.92) for vegans and lacto-ovo-vegetarians, respectively, compared with nonvegetarians.
- Diabetes Mellitus: The study examined the relationship between vegetarian diets and both prevalent and incident diabetes mellitus. The ORs for prevalent type 2 diabetes were 0.51 (95% CI: 0.40, 0.66) for vegans, 0.54 (95% CI: 0.49, 0.60) for lacto-ovo-vegetarians, 0.70 (95% CI: 0.61, 0.80) for pescovegetarians, and 0.76 (95% CI: 0.65, 0.90) for semivegetarians. For incident diabetes, the ORs for developing diabetes were 0.38 (95% CI: 0.24, 0.62) for vegans, 0.62 (95% CI: 0.50, 0.76) for lacto-ovo-vegetarians, 0.79 (95% CI: 0.58, 1.09) for pescovegetarians, and 0.49 (95% CI: 0.31, 0.76) for semivegetarians.
- Cancer Incidence: In multivariate adjusted analyses, vegetarians combined had a reduced risk of all cancers (HR: 0.92; 95% CI: 0.85, 0.99) and gastrointestinal system cancers (HR: 0.76; 95% CI: 0.63, 0.90).
- Mortality: After a mean follow-up of 5.79 years, vegetarians showed reduced all-cause mortality (HR: 0.88; 95% CI: 0.80, 0.97) compared to nonvegetarians.
Other Important Findings
- Bone Health and Protein Intake: The research indicated that lower protein intake, especially animal protein, was linked to a higher risk of wrist fractures. Plant-based protein sources appeared to be protective.
- Soy Milk and Bone Health: The study found that soy milk consumption was associated with improved bone health, similar to dairy products.
- Dietary Fiber and Macronutrients: The study provides details of the macronutrients, showing a higher amount of carbohydrates and fiber in the diets of vegans.
Limitations Noted in the Document
- Observational Nature: The study is based on observational data, which limits the ability to establish definitive causal relationships.
- Confounding Factors: Although the study attempted to adjust for potential confounders, it is possible that some uncontrolled factors may have influenced the results.
- Measurement Error: As with all nutritional studies, there is potential for measurement error in the assessment of dietary patterns.
- Generalizability: The study population mainly consists of Seventh-day Adventists in North America, which may limit the generalizability of the findings to other populations.
- Early Findings: The cancer incidence analysis was based on early follow-up data, which might not be sufficient to draw strong conclusions about the effect on specific cancers.
Conclusion
The initial findings from the Adventist Health Study 2 provide compelling evidence of the beneficial effects of vegetarian diets on various health outcomes. The study demonstrates that vegetarian dietary patterns are associated with lower BMI, reduced prevalence and incidence of diabetes, reduced risk of metabolic syndrome and hypertension, and decreased all-cause mortality. Moreover, it underscores the importance of plant-based protein sources for bone health and suggests a positive role of soy milk in bone health, comparable to dairy products. The observed differences in BMI, with the lowest values among vegans and increasing stepwise to nonvegetarians, suggest that the choice of diet plays a significant role in energy absorption and utilization. The study highlights the role of dietary patterns in mediating such a health effect, as the analysis shows that vegetarian diets reduced the odds of having metabolic syndrome. It is also noteworthy that in the context of cancer incidence, vegetarian diets, particularly vegan and lacto-ovo vegetarian diets, demonstrated an association with reduced risk. The findings suggest the need for the ongoing and future analyses to further elucidate the link between vegetarian diets and risk of specific cancers. The study also acknowledges the limitations of observational research, including the potential for residual confounding and measurement error. Nonetheless, the AHS-2 offers valuable insights into the relationship between diet and health, and these initial findings reinforce the importance of vegetarian diets for promoting overall well-being. As the research continues, this study will contribute significantly to our understanding of the complex relationship between dietary choices and human health, providing further guidance for dietary recommendations and promoting healthy lifestyles.