Individuals with metabolic syndrome (n = 15) were fed two hypocaloric diets, ~500 kcal below energy requirements, of individually prepared foods for 21 days. The diets consisted of a low-carbohydrate diet (LCD) (% carbohydrate:fat:protein = 7:74:20) and a low-fat diet (LFD) (55:28:20) reflective of the current US dietary recommendations. The LCD diet resulted in a net weekly intake of 2.69 g of arachidonic acid (ARA) in comparison to the 1.27 g/wk consumed during the LFD. The LCD significantly increased plasma ARA and decreased dihomo-gamma-linolenic acid (DGLA) in all three circulating lipid fractions as well as buccal cells in comparison to the LFD. Correlational analysis of plasma lipids with HOMA2 scores showed plasma ARA to be positively associated with insulin sensitivity in all three lipoprotein fractions during both diet phases. Total buccal cell ARA did not correlate to measures of insulin sensitivity in either diet phase, but DGLA was negatively correlated to insulin sensitivity during the LCD. The highly significant and consistent increase in circulating ARA after feeding a low-carbohydrate diet could be a result of multiple factors including better preservation of the existing ARA pool, increased dietary intake, greater endogenous synthesis and greater release into the circulation from adipose triglyceride stores. Given the importance of ARA in cellular membranes as it relates to insulin sensitivity, these results indicate that a low-carbohydrate diet promotes a favorable circulating and membrane fatty acid composition
