The Mediterranean diet is getting more attention because of its long-term benefits in terms of overall mortality and cardiovascular disease (CVD) risk.
The diet improves a wide range of metabolic parameters— including blood lipids, blood pressure, and insulin sensitivity—so it may be a good model diet to teach patients with renal disease. Studies have shown that adherence to a Mediterranean diet significantly improves creatinine clearance (QJM 2010;103:413-422).
Other potential benefits of the Mediterranean diet may include the higher intakes of phytates which, due to their ability to bind calcium, may reduce endothelium calcifications typically found in dialysis populations (Eur J Nutr 2010;49:321-326).
Calorie restriction in CKD
Overall caloric restriction, though, may be a confounding factor. For example, recent studies have indicated similar improvement in estimated glomerular filtration rate (eGFR) in chronic kidney disease (CKD) patients instructed to follow either low fat, low carbohydrate, or a Mediterranean diet (Diabetes Care 2013; published online ahead of print).
Similar results also occurred in the PREDIMED study, in which no significant improvements were found when a Mediterranean diet supplemented with either nuts or olive oil were compared with a control low fat diet (Am J Kidney Dis 2012;60:380-389).
Of note, further analysis has found that the Mediterranean diet supplemented with nuts induced a higher potential renal acid load and net endogenous acid production compared with the Mediterranean diet supplemented with olive oil (J Am Geriatr Soc 2009;57:1789-1798). The nut-supplemented group experienced significantly higher parathyroid hormone levels.
More recently, investigators have assessed Mediterranean diet adherence on a graded scale and the effect of adherence on metabolic parameters. In one study, (J Ren Nutr 2010;20:176-184), investigators assessed adherence using a validated diet score based on a method developed in the ATTICA study, which enrolled 3,042 men and women.
Intake of various food groups and wine is assigned a numerical value of 0-5 depending on the frequency with which they are consumed. These values are added to arrive at a score. The maximum score using this system is 55, which would indicate complete adherence.
A score of 0 would indicate non-adherence. Each 10-point increase in Mediterranean diet adherence was associated with a 3.7-unit increase in creatinine clearance in women and 10.1-unit increase in men. Fruit and moderate alcohol intake had the most positive intake on creatinine clearance, whereas red meat, potato, and poultry intake had the most negative impact.
Diet adherence and mortality risk
In a separate study, Huang et al. assessed the associations between Mediterranean diet adherence and mortality risk in CKD patients (Clin J Am Soc Nephrol 2013; published online ahead of print). The cohort consisted of 1,110 Swedish men enrolled in a prospective trial. Adherence to the Mediterranean diet was quantified on an 8-point scale. Eight different dietary components of the Mediterranean diet were assessed.
Each individual was categorically designated as compliant or noncompliant with a particular dietary component. If compliant, the participant was given a point for that component. A diet score of 2 points or less was considered low compliance; a score of 3-5 points and 6 points or more were considered medium and high compliance, respectively. Each 2-point increment in diet score was associated with a 12% decrease in CKD risk.
More specifically, those with the highest score had a 42% reduction in CKD risk compared with who had the lowest score. Interestingly, no typical metabolic parameters were found to be significantly different between groups.
Instead, most notable differences between groups existed in oral intakes of sodium, phosphate, and net endogenous acid production (NEAP). Of note, phosphate and net endogenous acid production were significantly lower in the high compliance group. After a 10-year follow-up, researchers found that each 2-point increment in diet score was associated with a 34% reduction in all-cause mortality. The highest compliance group had a 58% reduction in all-cause mortality compared with the lowest compliance group.
From a clinical perspective, teaching patients the Mediterranean diet model can be advantageous because it emphasizes an overarching style of eating rather than focusing on individual nutrients. Because people often eat mixed meals comprising several food groups and various macro and micro nutrients, single nutrient focus is often difficult for those not well-educated on the subject.