Can the incidence and mortality of chronic diseases be explained by dietary patterns?

From the ancient period to the current day, each cultural area has had their distinctive dietary pattern (combinations of dietary components, such as food or nutrients, to summarize a total diet) to adapt to their lifestyle and environments, such as a Western style diet (American style), Mediterranean diet and Asian diet (Japanese style). In recent years, chronic diseases such as diabetes, obesity, atherosclerosis, cardiovascular disease, and hypertension incidence and prevalence rate, have rapidly increased and have become a burden of public health management. Because lifestyle modification is the only confirmed preventive method for the rapid increase of these patients, several methods are recommended, such as nutritional modification and diverse exercise without drug therapy. In these lifestyle modification methods, dietary modification is extremely important for chronic disease prevention and management. So many dietary recommendations released by the international scientific committees and organizations state that a diet should be moderately low in caloric content, low in fat and carbohydrate content, and high in protein and fiber. These diets emphasize the reduction of carbohydrate intake and thereby encourage high protein intake, given that, in Western countries, high fat diets are also generally avoided. Many diets are low in carbohydrates and high in protein, such as the Atkins diet. Very low-carbohydrate diets typically contain <10% carbohydrates, 25–35% proteins and 55–65% lipids. For comparison, the average American diet contains 50% carbohydrates (275 g ⁄day), 15% protein (83 g ⁄day) and 35% lipids (85 g ⁄day). In the UK, the mean intake, as a percentage of total energy, is approximately 48% carbohydrates, 17% protein and 35% lipids. Hession et al. suggest that low-carbohydrate, high-protein diets were associated with a slightly greater increase in highdensity lipoprotein cholesterol and to a slightly greater decrease in triglycerides. In contrast, these diets were associated with a slightly greater increase in lowdensity lipoprotein cholesterol. Recently, low-carbohydrate and highprotein diets have become extremely popular with consumers and patients. However, concerns have been expressed about the health effects of low-carbohydrate and high-protein diets, even though little documented information exists about the long-term health consequences of low-carbohydrate and highprotein diets. Also these methods have not been fully confirmed for their benefit and usefulness by long-term, large, randomized clinical trials, but have only been found by short-term, small, randomized clinical trials and meta-analysis. Last year in Annals of Internal Medicine, Fung et al. published a very interesting article about all cause and causespecific mortality in a Nurses’ Health Study and Health Professionals’ Followup Study cohort. They examined the relationships of animal based or vegetable based fat and protein mixed low-carbohydrate diets with cardiovascular and cancer mortality over 20-years prospective follow up in two cohorts. They used a low-carbohydrate score, which was based on the percentage of energy as carbohydrate, fat and protein. They concluded that a lowcarbohydrate diet based on animal sources was associated with higher allcause cardiovascular and cancer mortality in both men and women, whereas a vegetable-based low-carbohydrate diet was associated with lower all-cause and cardiovascular disease mortality rates. Another three long-term observational studies on the effects of a long-term lowcarbohydrate diet on mortality were carried out. In a long-term cohort study of Swedish women, decreasing carbohydrate or increasing protein intake by one decile were associated with an increase in total mortality by 6% (95% CI 0, 12) and 2% (95% CI )1, 5), respectively. So, they concluded that low carbohydrate and high protein intake was associated with increased total and, particularly, cardiovascular mortality amongst women. During 10 years of follow up in Greek participants of the European Prospective Investigation Cancer and Nutrition study, higher intake of carbohydrates was associated with a significant reduction of total mortality, whereas higher intake of protein was associated with a non-significant increase of total mortality. Positive associations of low-carbohydrate and high-protein score were noted with respect to both cardiovascular and cancer mortality. Therefore, they suggested that prolonged consumption of diets low in carbohydrates and high in protein is associated with an increase in total mortality. In an elderly Swedish cohort study for 10.2-year median follow up, adjusted hazard ratios for the Mediterranean diet score were 0.71 (95% CI 0.55, 0.92) for all-cause mortality and 0.63 (95% CI 0.42, 0.96) for cardiovascular mortality, and the carbohydrate restricted diet scores were 1.19 (95% CI 0.97, 1.45) for all-cause mortality and 1.44 (95% CI 1.03, 2.02) for cardiovascular mortality. They concluded that adherence to a Mediterranean dietary pattern decreased mortality, but adherence to a carbohydrate-restricted dietary pattern increased mortality in elderly Swedish men. Another Asian population-based cohort study was divided into three major dietary patterns (vegetable-rich, fruit-rich and meat-rich) and followed up for 5.7 years. They reported that the meat-rich diet was associated with increased risk of diabetes (HR = 1.18; *Corresponding author. Tae Sun Park Tel.: +82-63-250-1794 Fax: +82-63-254-1609 E-mail address: [email protected] Received 10 April 2011; accepted 11 April 2011 COMMENTARY