Vegetarian Nutrition and Wellness
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Copyright Taylor & Francis Group. Do Not Distribute. The Role of Vegetarian 7 Diets in Weight Management Celine E. Heskey CONTENTS Summary ................................................................................................................ 114 7.1 Introduction .................................................................................................. 114 7.1.1 Overweight and Obesity ................................................................... 114 7.1.1.1 Prevalence .......................................................................... 114 7.1.1.2 Link to Morbidity and Mortality ....................................... 114 7.1.2 Weight Management ......................................................................... 115 7.1.2.1 Current Recommendations ................................................ 115 7.1.3 Why a Plant-Based Diet May Reduce the Prevalence of Overweight or Obesity .................................................................. 116 7.2 Observational Studies Examining the Relationship between Plant-Based Dietary Patterns and Measures of Adiposity ................................................ 116 7.2.1 Studies on Seventh-Day Adventists .................................................. 116 7.2.2 Studies on North American Populations .......................................... 136 7.2.3 Studies on European Populations ..................................................... 136 7.2.4 Studies on Other Populations ........................................................... 138 7.2.5 Findings of Body Composition Analyses ......................................... 138 7.2.6 Conclusions ....................................................................................... 140 7.3 Intervention Studies Examining the Effect of Plant-Based Diets on Measures of Adiposity ............................................................................. 140 7.3.1 Studies in Individuals with a History of Diabetes ............................ 141 7.3.2 Studies in Individuals with a History of Rheumatoid Arthritis ....... 157 7.4 Conclusion .................................................................................................... 159 7.4.1 Mechanisms ...................................................................................... 159 7.4.1.1 Nutrient Intake Trends in Plant-Based Patterns ................. 159 7.4.1.2 Implications of Dietary Patterns on Gut Microbiota ......... 160 7.4.1.3 Satiety ................................................................................ 161 7.4.2 Research Gaps .................................................................................. 161 References .............................................................................................................. 161 113 Copyright Taylor & Francis Group. Do Not Distribute. 114 Vegetarian Nutrition and Wellness SUMMARY Historically, observational studies have set the foundation for a relationship between plant-based dietary patterns and healthy weight status. Vegetarians, especially veg- ans, tend to weigh less than nonvegetarians and have a lower prevalence of overweight or obesity. Multiple studies, utilizing vegan and vegetarian dietary interventions, have demonstrated that plant-based diets may be successfully utilized in weight management treatment of overweight or obese individuals. Reduced energy, fat, and animal protein intake, and increased carbohydrate, fiber, whole grain, fruit, vegetable, and phytochemi- cal intake, help to explain some of the weight management benefits of these patterns. 7.1 INTRODUCTION 7.1.1 OVERWEIGHT AND OBESITY Overweight and obesity are global issues with significant health implications. Excess body weight has been linked to increased risk of chronic diseases, including cardio- vascular disease and diabetes mellitus (Bastien et al., 2014). Excess abdominal fat, particularly visceral adipose tissue, contributes to the etiological pathway of car- diometabolic risk factor aberrations, including insulin resistance, dyslipidemia, and hypertension (HTN) (Bastien et al., 2014). The definition of adiposity based on body mass index (BMI) (kg/m2), in most adult populations, is as follows: (1) underweight, <18.5 kg/m2; normal weight, 18.5– 24.9 kg/m2; (2) overweight, 25–29.9 kg/m2; and (3) obese, ≥30 kg/m2 (CDC, 2016d; WHO, 2016). Abdominal obesity can be assessed by measuring waist circumference. Individuals are considered to have abdominal obesity if their waist circumference is >88 cm for women or >102 cm for men (Bastien et al., 2014). Waist-to-hip ratio has also been used to assess disease risk, as it relates to abdominal obesity, but this mea- surement has been found to be a poor predictor of chronic disease in women (Lee and Nieman, 2013). Waist-to-hip ratios that are linked to increased disease risk are ≥0.8 for women and ≥0.9 for men (Lee and Nieman, 2013). Other ways that researchers can measure or estimate body composition (including excess adiposity) include using skinfold thickness measurements, air displacement plethysmography, bioelectrical impedance analysis (BIA), dual-energy x-ray absorptiometry (DXA), and magnetic resonance imaging (MRI), to determine percent body fat, fat mass, and fat-free mass (Lee and Nieman, 2013; CDC, 2016d). In regard to percent body fat, the ideal ranges are 6%–24% for men and 9%–31% for women (Lee and Nieman, 2013). 7.1.1.1 Prevalence According to the Centers for Disease Control (CDC), the prevalence of obesity in the United States is 36.5% in adults and 17% in children and adolescents (CDC, 2016a, 2016b). Worldwide the prevalence of overweight and obesity in adults is 39% and 18%, respectively (WHO, 2016). 7.1.1.2 Link to Morbidity and Mortality Overweight and obesity are risk factors for several of the top 10 causes of death in the United States, including heart disease, certain cancers, stroke, and diabetes Copyright Taylor & Francis Group. Do Not Distribute. The Role of Vegetarian Diets in Weight Management 115 (CDC, 2016c, 2017). Other health conditions that have been linked to obesity include dyslipidemia, HTN, gallbladder disease, osteoarthritis, and sleep apnea. Additionally, obesity contributes to increased disability or reduced quality of life, either directly or indirectly through previously mentioned diseases, or by increasing the occurrence of pain, decreasing mobility, and increasing risk of depression and other psychiatric ill- nesses (CDC, 2016c). It has been estimated that the cost in the United States to treat obesity is approximately $147 billion (2008) (CDC, 2016c). Obesity is also linked to an increased risk for early mortality. Overweight indi- viduals have a 11% higher risk of all-cause mortality than normal weight individuals (combined analysis of cohorts from North America, Europe, Asia, Australia, and New Zealand) (Global BMI Mortality Collaboration et al., 2016). In this same study, the hazard ratios (HRs) and 95% confidence intervals (CIs) were as follows: for grade 1 obesity (30.0–34.9 kg/m2), 1.44 (1.41, 1.47); for grade 2 obesity (35.0–39.9 kg/m2), 1.92 (1.86, 1.98); and for grade 3 obesity (40.0–59.9 kg/m2), 2.71 (2.55, 2.86), with normal weight as the reference (Global BMI Mortality Collaboration et al., 2016). 7.1.2 WEIGHT MANAGEMENT 7.1.2.1 Current Recommendations Realistic weight loss goals recommended by the Academy of Nutrition and Dietetics (AND) include 10% of baseline body weight over approximately 6–12 months (AND, 2014b). As little as 3%–5% of sustained weight loss can have cardiometabolic benefits, including improved triglycerides and blood glucose control. Greater losses have benefi- cial effects on blood pressure and cholesterol (AND, 2014b; Jensen et al., 2014; Raynor and Champagne, 2016). The current AND goal for weight loss is 5%–10% over 6 months (Raynor and Champagne, 2016). These goals are important to consider when evaluating the effectiveness of various dietary patterns for weight management. It should also be noted that the most effective weight management strategies include a combination of diet, physical activity, and behavior modification techniques (Raynor and Champagne, 2016). According to AND recommendations, it is essential for dietary weight loss inter- ventions to be hypocaloric (Raynor and Champagne, 2016). In its evidence analy- sis library, AND lists a hypocaloric lacto-ovo vegetarian diet as one of a multitude of dietary patterns or manipulations that may be effective for reducing excess weight (AND, 2014a). The 2013 American Heart Association/American College of Cardiology/The Obesity Society (AHA/ACC/TOS) recommendations for managing overweight and obesity in adults also includes hypocaloric lacto-ovo vegetarian and vegan diets as dietary treatment options for reducing weight (Jensen et al., 2014). The 2015–2020 Dietary Guidelines for Americans also includes a “Healthy Vegetarian Eating Pattern” as one of the healthy eating patterns recommended for reducing the risk of chronic diseases (DHHS and USDA, 2015). The Healthy Vegetarian Eating Pattern is a lacto-ovo vegetarian dietary pattern that is considered within the realm of options to help “achieve and maintain a healthy body weight” (DHHS and USDA, 2015). Assessment of plant-based dietary patterns, through either observational or intervention studies, demonstrates that individuals who follow these patterns ad libi- tum often have a lower average kilocalorie intake than those following a nonvegetar- ian or omnivore pattern (Farmer et al., 2011; Turner-McGrievy et al., 2015). Copyright Taylor & Francis