"Fleshing Out" the Benefits of Adopting a Vegetarian Diet.

D ietary and lifestyle changes remain the cornerstone of heart disease prevention. It has been estimated that >80% of cardiovascular events can be prevented with dietary and lifestyle modifications. Vegetarian diets are one approach to achieving a heart healthy dietary pattern, low in saturated and trans-fats and high in fiber and antioxidants. While other heart healthy dietary strategies such as lowcarbohydrate, low-glycaemic index and Mediterranean diets have been shown to reduce incidence of cardiovascular disease, recent meta-analyses have found that these diets do not consistently reduce low density lipoprotein-cholesterol (LDL-C), a major therapeutic blood lipid target to improve cardiovascular health. This lack of consistent effect represents a possible major barrier to recommending these diets to dyslipidemic individuals. The inconsistent lipid benefit with these dietary strategies relate to the higher consumption of saturated fats and an incomplete avoidance of red meat intake, both of which have been implicated in cardiovascular disease risk. Therefore, a complete avoidance of red meat consumption such as the vegetarian diet may represent a dietary strategy to which cardiovascular risk can be reduced through improving blood lipids. The cardinal feature of vegetarian diets is the absence of animal products, but there are those who claim to follow a vegetarian diet that include some forms of animal flesh. The variation in actual practice, thus has led to subtypes of vegetarianism: (1) pesco-vegetarians, who omit all animal products other than fish; (2) lacto-ovo-vegetarians, who omit all animal products but include eggs and dairy products; (3) lacto-vegetarians, who omit all animal products but dairy products; (4) ovo-vegetarian, which omits all animal products but eggs; and (5) vegans, who omit all animal products including honey. Although there is variation in the practice of vegetarian diets, the common underlying practice amongst them all is the avoidance of consuming red meat. This avoidance of red meat consumption may confer important blood lipid effects that other dietary strategies have not been able to produce. To provide high-quality evidence to assess the above relationship, Wang et al systematically review and metaanalyze the effects of vegetarian diets on blood lipids from randomized controlled trials to help assess the impact of vegetarian diets on cardiovascular risk, unconfounded by lifestyle habits. The 10 trials assessed the effects of vegetarian diets on blood lipids over an average of 24 weeks. The main finding is that vegetarian diets, compared with omnivorous diets, improve therapeutic targets for cardiovascular disease risk reduction including low-density lipoprotein cholesterol (mean difference [MD]= 0.34 mmol/L [95% CI: 0.57, 0.11]; P<0.001) and non-high-density lipoprotein cholesterol (HDL-C) (MD= 0.30 mmol/L [95% CI 0.50, 0.10]; P=0.04). There were also relative reductions in HDL-C (MD= 0.10 mmol/L [95% CI: 0.14, 0.06]; P<0.001), total cholesterol (MD= 0.36 mmol/L [95% CI: 0.55, 0.17]; P<0.001), with no effect on triglycerides (MD=0.04 mmol/L [95% CI: 0.05, 0.13]; P=0.40). The effect on low-density lipoprotein cholesterol alone would be expected to reduce coronary heart disease risk by 22% in someone with average lipid levels. Importantly, the meta-analysis also showed a large and important relative reduction in body weight (MD= 2.88 kg [95% CI 3.56, 2.20]; P<0.001). Thus it appears that vegetarian diets compared to omnivorous diets may improve body weight and blood lipids (except for HDL-C and TG), representing a dietary strategy that can improve cardiovascular risk through improvements on dyslipidemia. One potential concern noted in this meta-analysis is that HDL-C was significantly reduced on vegetarian diets, which may offset the observed health benefits. The observed effect, however, must be interpreted in context of the other findings. Although there was a significant reduction on HDL-C, other The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association. From the Department of Clinical Epidemiology and Biostatistics, Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada (V.H., R.J.dS.); Department of Nutritional Sciences, University of Toronto, Ontario, Canada (R.J.S.); Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, Ontario, Canada (R.J.S.). Correspondence to: Russell J. de Souza, RD, ScD, #32101280 Main St. West, Michael DeGroote Centre for Learning and Discovery (MDCL), Department of Clinical Epidemiology and Biostatistics, Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada L8S 4K1. E-mail: [email protected] J Am Heart Assoc. 2015;4:e002654 doi: 10.1161/JAHA.115.002654. a 2015 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell. 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