Effect of varying the fatty acid composition of a carbohydrate-restricted diet on plasma fatty acid composition, blood lipids oxidative stress, inflammation and insulin sensitivity in men

Background. Carbohydrate-restricted diets (CRD) consistently improve risk factors associated with Metabolic Syndrome (MetSyn). Recently, we showed that a saturated-fat rich hypocaloric CRD significantly reduced serum content of saturated fatty acids (SFA) and significantly increased arachidonic acid (AA) and the omega-6/omega-3 polyunsaturated (PUFA) ratio while significantly decreasing inflammation compared to a low-fat diet. This disconnect between dietary and circulating lipid lead us to explore how varying the fat composition of a CRD affects these variables, in addition to oxidative stress. ^ Methods. Eight healthy weight-stable men (age 45 ± 7.9 y, body fat 28.4 ± 6.5%) were fed two eucaloric CRD varying in saturated fat and unsaturated fat with the same macronutrient distribution (12%en carbohydrate, 30%en protein, 58%en fat, 850 mg cholesterol) for 6 weeks each without weight loss. Similar foods were fed but CRD-SFA emphasized dairy fat while CRD-UFA emphasized olive oil, omega-3 fortified eggs, salmon, and walnuts. CRD-SFA provided almost twice as much SFA (86 g vs 47 g) and less monounsaturated fat (MUFA) and omega-6 and omega-3 PUFA than CRD-UFA, confirmed by chemical analysis. Fasting blood and 24 hr urine was analyzed at baseline and following each diet for fasting lipoproteins, insulin, glucose, inflammatory markers, fatty acid composition in plasma triacylglycerides (TAG), phospholipids (PL) and cholesteryl esters (CE), and urine 8-iso PGF2α. ^ Results. Regardless of fat quality, both CRD significantly decreased TAG and insulin, and increased HDL-C and LDL particle size (P \u3c 0.05). Despite increased total-cholesterol (TC) and LDL-cholesterol (LDL-C) after CRD-SFA, the TC/LDL-C ratio was not different between diets. Total plasma SFA in CE, PL, and TAG were unchanged after the CRD-SFA, and plasma PL and CE AA content was significantly increased. CRD-UFA significantly increased PL and CE EPA+DHA content and the PL omega-3 index. Inflammation was not different between diets or compared to baseline, but urinary 8-iso PGFza was significantly lower than baseline following CRD-UFA (-32.4%). PL AA was significantly inversely correlated to 8-iso PGF2α with both diets. ^ Conclusion. Regardless of SFA content, CRD positively influence risk factors associated with MetSyn and do not increase plasma SFA content. Elevated plasma AA following a high-SFA CRD does not have deleterious effects while replacement of some SFA with MUFA and omega-3 PUFA significantly decreased plasma SFA, increased omega-3/omega-6 PUFA ratio and reduced oxidative stress as measured by lower urinary 8-iso PGF2α.