Coronary artery disease is the leading cause of death in many countries, but its prevalence has changed significantly during the last 50 years. Death rates from heart disease have fallen dramatically in western countries, but increased in many ‘developing’ countries. These large population-wide changes suggest environmental factors, including diet, are a major determinant of the risk of heart disease. A typical western dietary pattern has been widely considered to be unhealthy, because it contains more processed foods, which can increase obesity and diabetes, and salt, which can increase blood pressure. For many years, foods containing saturated fat have also been thought to increase the risk of heart disease. Of ‘healthy’ diets, most evidence favors a Mediterranean dietary pattern, which includes fruits and vegetables, whole grain foods, fish, little meat, modest alcohol, and olive oil.
Although diet is likely to be an important determinant of heart disease risk, and much research has been undertaken, there is continued controversy over which foods are beneficial and which are hazardous. One problem is that diet is complex and includes many foods, so the influence of individual foods is difficult to determine. Another issue is that risk factors for heart disease act over years during which diet may change. Many studies have evaluated associations between diet and markers of heart disease risk, such as blood pressure, cholesterol levels, or measures of inflammation. However, diet could influence risk by other pathways, so relying on these surrogate measures could be misleading. A further problem is that an unhealthy diet may be associated with other adverse lifestyle ‘risk factors’ such as a sedentary lifestyle, smoking, and socio-economic deprivation, which could explain health problems thought to be from a poor diet. The most reliable evidence comes from clinical trials where participants are randomized to one diet or another, and outcomes followed over several years. However, randomized trials of diet are very hard to undertake and few have been done.
The European Heart Journal recently reported the results of a large study, which evaluated dietary patterns in over 15,000 patients with stable coronary heart disease from 39 countries. Subjects were participating in the ‘STABILITY’ trial, which was primarily designed to evaluate a novel medication, darapladib, which turned out not to influence cardiovascular risk. At the start of the study, a simple questionnaire asked participants how often they ate common food groups. Two dietary patterns were evaluated; a ‘Mediterranean’ pattern, which is characterized by a greater consumption of whole grains, fruits, vegetables, legumes, fish, and alcohol, and less meat; and a ‘western pattern’ characterized by greater consumption of refined grains, sweets and deserts, sugared drinks, and deep fried foods. During nearly four years follow-up, individuals who most closely followed a ‘Mediterranean dietary pattern’ were about one third less likely to die, or to suffer a heart attack or stroke, after statistical adjustment for all other factors. In contrast, and to our surprise, there was no relationship between the ‘western dietary pattern’ and these adverse outcomes. The benefits associated with a high ‘Mediterranean diet score’ were consistent across many countries, but the study could not evaluate the importance of individual foods. These observations suggest the healthy types of foods included in the Mediterranean diet score are likely to be beneficial. Foods in this dietary pattern can be part of widely varying diets around the world, many of which are not in a ‘traditional Mediterranean diet’.
Dietary advice has traditionally focused on avoiding ‘unhealthy’ processed foods, which are a major contributor to obesity. However this study is part of increasing evidence which suggests less ‘healthy’ foods, which are increasingly consumed globally, may not be the major cause of cardiovascular disease. It is possible dietary advice which emphasizes the importance of ‘healthy’ foods, including at least three servings of fruit and vegetables each day, may be more positively received, and more successful for lowering the risk of heart disease and stroke.
Professor Ralph Stewart is a Cardiologist at Auckland City Hospital, Auckland, New Zealand. He is part of an international team who undertook the STABILIY trial, and who are currently undertaking further research on the role of lifestyle, genes, and novel blood markers in patients with coronary heart disease. He is also an author of the recently published “Dietary patterns and the risk of major adverse cardiovascular events in a global study of high-risk patients with stable coronary heart disease”.