Diet Recommendations for Obesity Prevention: Time to Ditch Diversity

Ample evidence supports the role of unhealthy eating patterns and dietary choices with obesity, poor cardiometabolic health, and adverse cardiovascular outcomes.¹ An estimated 318,656 (95% confidence interval [CI] 306,064 to 329,755; 45.4%) of the 702,308 cardiometabolic deaths (coronary heart disease, stroke, heart failure, and type 2 diabetes) were attributed to suboptimal dietary intake in US adults in 2012.² Alarmingly, the previous decline in death rates attributable to diabetes and cardiovascular disease (CVD) in the US has now essentially plateaued with age-adjusted death rates of 21.0 (95% CI, 20.9- 21.2) per 100,000 and 218.2 (95% CI, 217.7-218.6) per 100,000 for diabetes and CVD, respectively.^{3, 4} One possible explanation of the flattening of cardiometabolic death rates could be the obesity epidemic and consequent adverse changes in risk factors (RF) as population-based prevalence of obesity in the United States has increased significantly and 39.6% (95% CI, 36.1%-43.1%) of adults and 18.5% (95% CI, 15.8%-21.3%) of youths are obese according to NHANES 2015 to 2016.^{5, 6} Despite major health promotion efforts by the American Heart Association (AHA) and others, strategic goals for lowering the burden of CVD set by the AHA and Million Hearts Initiative are unlikely to be reached if current trends continue.

Optimization of diet quality and intake has been a long-standing cornerstone of primordial, primary, and secondary prevention efforts.^{7, 8} The goals of dietary guidelines have shifted dramatically from prevention of clinical nutrient deficiencies (e.g. thiamine resulting in beriberi) towards recommendations to limit intake of specific nutrients (e.g. saturated fats, sodium) in the context of the growing obesity epidemic and awareness of dietary contributions to increasing burden of obesity, diabetes, and CVD. The 2015 to 2020 Dietary Guidelines for Americans recommends focusing on diet variety, defined as a diverse assortment of foods and beverages.⁹ In response to the clear lack of consensus surrounding this recommendation, the writing group for the AHA Scientific Advisory, “Dietary Diversity: Implications for Obesity Prevention in Adult Populations” comprehensively reviewed the available literature on dietary diversity and evaluated its association with obesity outcomes. Multiple measures and analytical techniques for assessing diet diversity on a population level have been studied, including count-based scores, evenness, and dissimilarity, with no standardized measure for dietary diversity. The authors highlight the limitations of these studies using these measures of diversity, including differences in the number of food groups used across different investigations, weak correlation among the different measures, and lack of multivariable adjustment for sociodemographic and lifestyle factors. Finally, it is important to point out that diet diversity does not incorporate assessment of diet quantity (caloric intake) or quality (health value), which are clearly associated with cardiometabolic outcomes and CVD.^{10, 11}

In response to the concerning trends in CVD burden, the AHA developed and defined a bold new concept of “cardiovascular health” (CVH) in 2010 as part of the AHA’s Strategic Impact Goal Statement in 2010 to improve CVH by 20% by 2020, which included an innovative definition of a healthy dietary pattern that promotes cardiovascular health as intake of the following 5 dietary components: 4.5 cups/day of fruits/vegetables, 2 servings of fish per week (3.5oz), 3 servings of whole grains per day (1oz), <1500 mg/day of sodium, and <450 kcal/week of sugar-sweetened beverages scaled to a 2000 kcal/day diet.¹² The full spectrum of CVH incorporates presence and levels of health behavior metrics (diet, physical activity, body mass index, smoking status) and health factor metrics (cholesterol, blood pressure, and fasting glucose). Adoption and maintenance of a healthy diet has been shown to be associated with a lower CVD risk profile from young adulthood to middle-age and is an important area of focus to prevent CVD.^{13, 14} Yet, achievement and maintenance of an ideal diet remains consistently suboptimal and the lowest-rated health factor at <5% in both children and adults.15-18 If current trends continue, the projected prevalence by 2020 of an ideal healthy diet score is only 1.2% (0.3-2.1%) in men and 1.9% (0.8-2.8%) in women.¹⁵

Adding complexity to dietary guidelines and recommendations is the varying strength and association of specific dietary components regarding prevention of CVD and promotion of CVH. Two of the key metrics composing an ideal diet based on the AHA CVH score that should be highlighted in dietary recommendations and efforts to reduce burden of CVD is reduction of sodium and sugar-sweetened beverage consumption. There is strong and consistent evidence on the adverse health effects of excess sodium intake in the pathogenesis of hypertension, left ventricular hypertrophy, and development of CVD that spans preclinical, epidemiological, and clinical studies.^{19, 20} There is clear and convincing clinical trial evidence supporting blood pressure-lowering effect of reduction of sodium intake in adults with prehypertension and hypertension.^{21, 22} Achievement of a national target of <2,300 mg/day sodium consumption could potentially prevent or postpone 450,000 CVD events (95% CI 240,000 to 740,000) and potentially generate 2.1 million (95% CI 1.7-2.4 million) discounted quality-adjusted life years between 2017 and 2036 based on the US IMPACT Food Policy model.²³ Sodium consumption in the US far exceeds this target with average sodium intake of 3746 mg/day reported in participants with hypertension from the National Health and Nutrition Examination Survey.²⁴ However, reduction of sodium intake on an individual-level can be very difficult to achieve given the ubiquity of sodium in the US food supply and will require changes on a policy-level in food manufacturing and processing.²⁵ Increases in intake of added sugars through soft drinks and sugar-sweetened beverages has increased dramatically between 1970 and 2000 from 7.8 to 13.2 ounces and accounts for 50% of the increase in total caloric intake, coinciding with the increasing prevalence in obesity and diabetes over this time period.^{26, 27} While data from randomized controlled trials are limited, numerous epidemiological studies demonstrate the adverse health effects of sugar-sweetened beverages on obesity, diabetes, and CVD and support the recommendations to limit intake of added sugars.^{28, 29}

In order to curb the CVD epidemic and even, eliminate the burden of CVD (CVD Endgame), action and partnership is required at both an individual level and population level engaging key stakeholders (healthcare providers, professional organizations, public health agencies, governments, and industry) with a focus on achieving and maintaining healthy dietary intake from early life. Successful strategies could include calorie labeling, sugar-sweetened beverage taxes, trans-fat bans, and other public health policies. As identified by the AHA writing group, recommendations focusing on dietary diversity are outdated and lack sufficient data in our contemporary era of nutrient overconsumption and emphasis should be shift towards heart-healthy eating patterns.