Nutrition Intervention on Cardiovascular Risk Factors in Healthy Individuals

Glass Half Empty or Half Full?

Corresponding Author

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• cardiovascular disease
• mediterranean diet
• nutrition
• risk factors

Unhealthy diet, lack of physical activity, and smoking are important causes of preventable chronic diseases such as cardiovascular disease (CVD), diabetes, obesity, and even cancer (1). Consistent epidemiological evidence indicates that an unhealthy lifestyle contributes nearly 80% of population-attributable cardiovascular risk (2–4). Recommendations from governments (5) and scientific societies (6–8) have focused on reducing CVD burden through promotion of a healthy lifestyle. The 3 dietary patterns recommended by the U.S. Dietary Guidelines are the healthy American diet, the Mediterranean diet and the vegetarian diet (5). The Dietary Approaches to Stop Hypertension (DASH) diet and the portfolio diet (9) are also healthy dietary patterns recommended by the American Heart Association (AHA)/American College of Cardiology guidelines (6) and Canadian Cardiovascular Society guidelines (8), respectively. These diets are plant-based and share a high consumption of fruit, vegetables, legumes, nuts, whole grain cereals and fish, and reduced consumption of red meats, processed meat products, refined cereals and sugar-added foods and drinks. The Mediterranean diet additionally includes olive oil for cooking and dressing and moderate wine consumption (10), and the DASH diet emphasizes reduction in salt intake (11).

Official guidelines and media attention have increasingly focused on foods and dietary patterns that help curb chronic disease and promote healthy aging but to questionable effect. In a representative sample of more than 35,000 U.S. adults free of CVD, physical activity levels and low diet-quality scores changed minimally from 1988 to 2008, whereas a decline in the prevalence of smoking, high blood cholesterol, and high blood pressure coincided with increases in the prevalence of hyperglycemia and obesity (12). In another analysis of 29,124 adults of the same population survey, the quality of diet improved slightly during a 12-year period but remained poor overall, particularly among persons of lower socioeconomic status (13). In Europe, the scenario is similar. In the EUROASPIRE (European Action on Secondary Prevention through Intervention to Reduce Events) IV (2014 to 2015) survey in more than 6,700 coronary patients from 14 European regions, a large proportion did not achieve lifestyle changes or therapeutic risk factor targets (14). The proportion of patients who practiced a reasonable level of exercise (physical activity of at least 20 min >3 times/week) was low (20%), and adherence to a healthy diet was still lower.

In this issue of the Journal, Jenkins et al. (15) report results of a 6-month randomized clinical trial of dietary advice, with and without food provision, on weight loss and cardiovascular risk factor levels in healthy overweight or obese adults. A control group received the Health Canada’s food guide without further advice. The trial’s 3 treatment arms included advice to follow the DASH diet plus the dietary portfolio of cholesterol-lowering foods; weekly provision of a food basket reflecting this advice; or food delivery plus advice. Additional intervention consisted of 30-min telephone interviews, administered weekly in the first month and monthly in the remaining 5 months. Participants were followed for up to 18 months after entering the study. Retention in the trial was best for participants given food baskets. At 6 months, there were small increases in consumption of vegetables, fruit, and whole grain servings in the 4 groups, but significant increases in portfolio foods were only observed in those given these foods for free. All groups modestly increased vegetable protein and reduced saturated fat intake. Curiously, only participants in the control group significantly reduced caloric intake. Small beneficial changes were observed in weight, waist circumference, blood pressure, blood glucose, and lipid profile, without among-group differences. Changes in food consumption and risk factors tracked reasonably well at 18 months.

Participants had no CVD risk factors except for increased adiposity, but the results are in line with those of trials of intensive lifestyle counseling in persons with CVD risk factors, showing modest reductions of blood glucose and cholesterol levels, body weight, and blood pressure, besides reduced incidence of diabetes at 12 to 24 months (16).

The authors of this large and well-conducted nutritional intervention trial appeared discouraged to find that the interventions resulted in only modest increases in consumption of recommended foods or reductions in cardiovascular risk factors, regarding the glass as half empty. However, the glass can be seen rather as half full. First, study subjects were self-selected, motivated, educated, and except for their obesity, quite healthy, with blood pressure and cholesterol levels lower than expected in a Western population of similar age. The so-called healthy participant effect was at work here, namely, the lower risk factor levels are the less can they be reduced by any intervention. Second, even small changes in risk factors can be associated with clinically meaningful reductions in CVD events, as shown for cholesterol and blood pressure in seminal epidemiologic studies (17,18). Third, the diets recommended were calorie-unrestricted, yet small beneficial changes in body weight and waist circumference (−0.9 kg and −1.4 cm, respectively) were still observed at 18 months. In a non-intervened Western population cohort of similar demographic characteristics, one would have expected small gains in adiposity during the study period. Finally, although participants’ baseline diets were reasonably good, they made small improvements that were not completely lost 12 months after termination of active intervention. That this also occurred in the control group 18 months after receiving just a copy of healthy nutrition guidelines is no small feat.

Two further aspects merit attention. First, providing foods at no cost upgraded dietary adherence and improved retention. We had a similar experience in the PREDIMED (Prevención con Dieta Mediterránea) trial, wherein the Mediterranean diet intervention groups were given free extra-virgin olive oil and mixed nuts throughout the study (10). However, when only dietary advice is given in a nutritional intervention trial, changing dietary habits is difficult even in motivated persons, as attested to by the results of the group given advice only in the study of Jenkins et al. (15). In the PREDIMED trial, control group participants were advised to reduce all dietary fat but received no low-fat foods. After follow-up for 5 years, they only managed to decrease total fat intake by 2% of daily energy, from 39% to 37% (10). The large Women’s Health Initiative trial of low-fat diet for prevention of CVD, cancer and other outcomes also fell short of fat reduction targets (19). Small dietary changes occurred as well in trials of lifestyle intervention for CVD risk factor reduction (16).

A second interesting aspect is the “legacy effect” of the nutritional intervention observed in this trial (15); benefits of the intervention on CVD risk factors extend beyond the finite period of active treatment. This phenomenon has been seen in several other (i.e., nutrition) trials, and has been documented even 40 years after termination of one trial (20). Performing large, well-designed, long-term dietary trials with CVD events as endpoints is difficult, very expensive and entails several years of follow-up. Only 3 large trials of dietary patterns of CVD prevention have been published in the last 2 decades: PREDIMED (10), Women’s Health Initiative (19), and Look AHEAD (The Action for Health in Diabetes) (21), the last one including increased physical activity and dietary management. Small, shorter-term trials with outcomes on intermediate markers like that of Jenkins et al. (15) are also difficult but manageable, particularly if specific foods are delivered to participants in the active treatment group.

The key question still is how to entice the general population to adhere to healthy dietary patterns. The AHA recommends several strategies to improve dietary habits and increase physical activity in order to reduce CVD burden: 1) sustained focused media and educational campaigns; 2) labeling and consumer information; 3) lower prices of healthy foods through reduced taxes or other economic incentives; 4) campaigns in schools and workplaces; 5) local environmental changes to increase availability of healthy foods; and 6) restrictions on advertising and marketing of unhealthy foods (22). Such substantial changes are always slow. Each country and scientific society must prioritize the strategies best adapted to local customs and regulations. However, it appears that simply giving a copy of healthy dietary guidelines causes small changes in the right direction. Perhaps we should start with this extremely simple, no-cost procedure at schools, workplaces, clinics, or sports centers, while the other strategies are slowly developed and implemented.

• American College of Cardiology Foundation