In Focus DASH-ing toward improved renal outcomes: when healthy nutrition prevents incident chronic kidney disease

Chronic kidney disease (CKD) affects a substantial proportion of the general population worldwide [1]. The burden of CKD on affected individuals and on the society are now welldocumented [2], emphasizing the need for better preventive efforts. Treatment of well-known risk factors such as hypertension or diabetes mellitus can be applied to this end, but interventions that could be applied to the wider general population (e.g. life style modification) are less well defined. Healthy nutrition can indeed be envisioned as such an ‘intervention’, in that diets consisting of proper amounts and quality of nutrients could have potentially far reaching positive consequences. One such dietary intervention, the DASH (Dietary Approaches to Stop Hypertension) diet, has been particularly well studied. The DASH diet is rich in fruits, vegetables, low-fat dairy products, potassium, calcium, magnesium and fibers, while it is low in saturated fat, sodium, added sweeteners and other sugars and additives such as inorganic phosphorus (Table 1). The macronutrient breakdown of the classical DASH diet is approximately 55% carbohydrates, 18% protein and 27% fat as the source of energy, but there are different DASH versions [3]. The DASH emphasizes healthy sources of protein, such as, lean meats, nuts, seeds, and legumes as well as complex carbohydrates such as whole grains. The original purpose of the DASH diet was to lower blood pressure in patients with prehypertension or stage I hypertension [4]. Subsequent secondary analyses and observational studies have suggested that consumption of the DASH diet is also associated with lower incidence of coronary heart disease and stroke [5, 6]. The association of the DASH diet with CKD has also been examined in selected Western populations, suggesting a potential protective effect [7, 8]. One potential problem inherent of even the best-designed clinical trials is their limited external validity; i.e. their results apply primarily to patients whose characteristics are similar to those of the original trial participants [9]. This issue is particularly compelling when we try to extrapolate a dietary intervention to populations from countries with a vastly different socio-cultural milieu, as their dietary habits and the available nutrients could be fundamentally different. It is thus very important that interventions examined in Western populations are tested in other countries to determine the degree to which they could confer similar benefits. Such a confirmatory study was conducted by Asghari et al. and is published in this issue of Nephrology Dialysis Transplantation [10]. The investigators used a prospective health survey conducted in Tehran (the Tehran Lipid and Glucose Study) to select randomly a group of 3462 participants for a dietary assessment, of which 1630 individuals were included in the present analysis. Participants completed a detailed, validated food frequency questionnaire, which was used to determine their adherence to a DASH-style diet, and to quantify the various components of their diet. Participants were followed for a median of 6.1 years, and the outcome of interest was incident CKD, defined as the occurrence of an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m. Adherence to a DASHstyle diet was associated with a 60% lower incidence of CKD after adjustment for a battery of confounders. When examining individual components of the DASH diet, higher consumption of fruits, whole grains, nuts and legumes was also associated with lower incidence of CKD [10]. The health benefits of a DASH-style diet are potentially farreaching, although the mechanisms whereby a DASH diet