The Impact of Diet on Cardiovascular Risk

The data come from the Dietary Approaches to Stop Hypertension (DASH) trial, which gave us the DASH diet. The DASH diet begins with a reduction of sodium; it was, after all, designed to reduce hypertension. It also emphasizes eating fruits, vegetables, and grains and restricting calories to about 2000 daily. 437 participants were randomized to receive the DASH diet, a diet high in fruits and vegetables, or a control diet. The researchers calculated the 10-year risk of a cardiovascular event using a popular equation based on blood pressure and lipid profiles before and after completing an 8-week treatment. [1]

Cardiovascular Risk – the Pooled Cohort Equation (PCE)

This mathematical model was introduced ten years ago and has been used as a tool to define the risk of an untoward cardiovascular risk over ten years. It was empirically derived from prospective studies involving age, gender, race, smoking status, blood pressure, hypertension and diabetes status, and total and HDL cholesterol levels. It has been used as a standard guide for physicians in counseling their patients. As with other algorithmic risk calculators, its performance varies as the population shifts away from the original study group, causing over and underestimation of risk.

Changes in cardiovascular risk in this study were based upon changes in total and HDL cholesterol and systolic blood pressure (the first and higher number).

Results

• The DASH diet lowered systolic blood pressure, total and HDL cholesterol more than either the control or fruit and vegetable diet.
• The DASH diet and fruit and vegetable diets lowered cardiovascular risk, after 8 weeks, by about 10%

Even between these two “good” diets, there were tradeoffs. Specifically, DASH had a more pronounced reduction in systolic blood pressure (that was how it was designed), but this was mitigated by the more significant improvement in HDL in the fruits and vegetable diet.

Before you rush out to the grocery store

The good news is that the DASH trial was more diverse than other studies, but the improvement in risk factors with diet was twice as significant for women and four-fold greater for Blacks. 

“This is particularly relevant as dietary pattern has been identified as one of the most important mediators of hypertension risk among Black adults…. The impact of disparities on access to healthy foods has been a major focus of policy effects to promote higher intake of fruits and vegetables among Black adults.”

Disparities in access to nutritional foods, i.e., fruits and vegetables, are only part of the problem. As I discussed previously, the use of salt in cooking varies regionally in the US as it does in China. The role of systolic blood pressure, which is related, in part, to salt intake, was the primary driver of risk reduction in this study, so our culinary preferences may be equal or greater drivers of risk than access to fruits and vegetables. We just do not know.

The other consideration is the size of the dietary effect, a 10% reduction over ten years. Is this improvement clinically meaningful? In this instance, it seems to be for those at greater risk, blacks and women. Still, I am not sure I would give up the occasional steak Frites for that decline in risk, especially if I am, in general, pursuing a more “plant-based” diet when I can and getting off the couch to exercise every day.

[1] The control diet was high in fat, saturated fat, and cholesterol, with roughly 25% of the average amount of potassium, magnesium, and calcium customarily consumed. The fruit and vegetable diet provides more of these foods and has more potassium and magnesium. DASH had more fruits and vegetables than the control, along with grains, poultry, fish, and nuts. It “emphasized fat-free or low-fat dairy products, with reduced saturated and total fat, cholesterol, sweets, and sugary beverages.”

Source: Effects of Diet On 10-year Atherosclerotic Cardiovascular Disease Risk (from the DASH Trial) American Journal of Cardiology DOI: 10.1016/j.amjcard.2022.10.019