Promotion of food over supplementation has long been thought to be ideal. However, data demonstrating effectiveness of diet alone has been lacking, especially related to omega-3 fatty acids. Long-chain omega-3 fatty acids have been shown to decrease inflammation by reducing the production of inflammatory mediators and the expression of adhesive molecules.

These long chain fatty acids are found in oily foods such as those listed in the Table 1 (See below). As the table shows, a tablespoon of flaxseed oil is comparatively high in omega-3 fatty acids. The two most common omega-3 fatty acids are eicosapentaenoic (EPA) and docosahexaenoic acid (DHA).

In an Australian study, 2,514 subjects aged 49 years or older were followed over 15 years to examine the relationship between intake of omega-3 fatty acids and death from inflammatory diseases. Women in the highest tertile of total omega-3 fatty acid intake at baseline had a significant 44% reduced risk of death compared with those in the lowest tertile (Am J Clin Nutr 2011;93:1073-1079).

The researchers did not observe this association in men. In a separate analysis, investigators found that each standard deviation increase in long-chain omega-3 fatty acid intake was associated with a 13% decrease in chronic kidney disease (CKD) risk.

Omega-3 intake: ratio is important

Another study (Br J Nutr 2011;105:1361-1368) found that each standard deviation increase in α-linolenic acid (an omega-6 fatty acid) was associated with an 18% increase in CKD risk. In addition, compared with subjects in the lowest quartile of intake, those in the highest quartile had a 31% decreased risk of CKD. This study revealed the importance of the omega-6 to omega-3 ratio in the diet.

Historically, the intake ratio of omega-6 to omega-3 fatty acids was more equivalent; however, in the modern diet, which contains lower amounts of fish and nuts, the ratio favors omega-6 fatty acids. Estimates of the ratio of omega-6 to omega-3 fatty acids in the western diet are of 15 to 1 or higher (Biomed Pharmacother 2006;60:502-507).

In a study of 145 hemodialysis (HD) patients, a team led by Kamyar Kalantar-Zadeh, MD, MPH, PhD, examined the association of both the ratio of omega-6 to omega-3 fatty acids and the intake of omega-3 fatty acids alone with serum C-reactive protein (CRP), a marker of inflammation, and mortality (Am J Kidney Dis 2011;58:248-256). The researchers collected data on dietary intake using a three-day diet record.

The subjects, who participated in the Nutritional and Inflammatory Evaluation in Dialysis study, had a median intake of omega-3 fatty acid of 1.1 g/day (25th-75th percentile, 0.8-1.6 g/day) and a median ratio of omega-6 to omega-3 intake of 9.3 (25th-75th percentile, 7.6-11.3 g/day). This median intake is lower than documented for the Western diet but is still high in omega-6 versus omega-3 fatty acids. Interestingly, patients in the highest omega-3 quartiles also had high intakes of energy, cholesterol, fiber, total fat, and omega-6 fatty acids but lower intake ratios of omega-6 to omega-3 fatty acids.

Subjects had a mean age of 53 years and 43% of them were women and 42% were African Americans.

Measuring inflammation

To measure the relationship of inflammation to the omega-6 to omega-3 intake ratio, multivariate regression models were conducted where the change in CRP over 12 months was predicted by the fatty acid ratio. Each one unit increase in ratio was associated with a significant 0.55 mg/L increase in CRP, indicating that the higher the ratio the more inflammation was present. The investigators also examined death risk by quartile of omega-6 to omega-3 fatty acid ratio. The lowest quartile of ratio was associated with the lowest risk of death.

The authors explained that mammalian cells cannot convert omega-6 into omega-3 fatty acids because they lack the converting enzyme, omega-3 desaturase. Vegetable oils rich in omega-6 have displaced other fats in the American diet, they observed, because of evidence of their hypocholesterolemic properties.

These aforementioned studies indicate that promoting foods high in omega-3 fatty acids may be beneficial in reducing inflammation and risk of death in patients with CKD.

 

Table 1

Foods containing omega-3 fatty acids

 

Food item

mg of omega-3 fatty acids

Flaxseed Oil, 1 tsbp

7196

Salmon, 1 tbsp

4767

Cod Liver Oil, 1 tbsp

2664

Walnuts, 1 tbsp

1271

Margarine, 1 tbsp

705

* Source of data = USDA’s National Nutrient Database for Standard Reference