Limited effect of dietary saturated fat on plasma saturated fat in the context of a low carbohydrate diet.

Abstract

"We recently showed that a hypocaloric carbohydrate restricted diet (CRD) had two striking effects: (1) a reduction in plasma saturated fatty acids (SFA) despite higher intake than a low fat diet, and (2) a decrease in inflammation despite a significant increase in arachidonic acid (ARA). Here we extend these findings in 8 weight stable men who were fed two 6-week CRD (12%en carbohydrate) varying in quality of fat. One CRD emphasized SFA (CRD-SFA, 86 g/d SFA) and the other, unsaturated fat (CRD-UFA, 47 g SFA/d). All foods were provided to subjects. Both CRD decreased serum triacylglycerol (TAG) and insulin, and increased LDL-C particle size. The CRD-UFA significantly decreased plasma TAG SFA (27.48 ± 2.89 mol%) compared to baseline (31.06 ± 4.26 mol%). Plasma TAG SFA, however, remained unchanged in the CRD-SFA (33.14 ± 3.49 mol%) despite a doubling in SFA intake. Both CRD significantly reduced plasma palmitoleic acid (16:1n-7) indicating decreased de novo lipogenesis. CRD-SFA significantly increased plasma phospholipid ARA content, while CRD-UFA significantly increased EPA and DHA. Urine 8-iso PGF(2α), a free radical-catalyzed product of ARA, was significantly lower than baseline following CRD-UFA (-32%). There was a significant inverse correlation between changes in urine 8-iso PGF(2α) and PL ARA on both CRD (r = -0.82 CRD-SFA; r = -0.62 CRD-UFA). These findings are consistent with the concept that dietary saturated fat is efficiently metabolized in the presence of low carbohydrate, and that a CRD results in better preservation of plasma ARA."

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Modification of lipoproteins by very low-carbohydrate diets.

Abstract

"Very low-carbohydrate diets (VLCDs) are popular, but remain controversial. This review summarizes the latest studies that have examined the effects of VLCDs on lipoproteins and related risk factors for cardiovascular disease. Prospective studies indicate that VLCDs improve the lipoprotein profile independently of weight loss. Although not as effective at lowering LDL cholesterol (LDL-C), VLCDs consistently improve postabsorptive and postprandial triacylglycerols (TAGs), HDL cholesterol (HDL-C), and the distribution of LDL-C subfractions to a greater extent than low-fat diets. VLCDs also improve proinflammatory markers when associated with weight loss. Studies usually report mean lipid responses, but individual data indicate a large degree of variability in the magnitude and in some cases the direction (e.g., LDL-C) of lipoprotein responses to both low-fat and VLCDs. Such variability makes it hard to defend a single diet recommendation, especially considering the potential for low-fat/high-carbohydrate diets to exacerbate TAG, HDL-C, and other characteristics of the metabolic syndrome. Considering the effectiveness of VLCDs in promoting fat loss and improving the metabolic syndrome, discounting or condemning their use is unjustified. We encourage a more unbiased, balanced appraisal of VLCDs."

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