The effects of a carbohydrate restricted diet with and without supplemental soluble fiber on cardiovascular risk and lipoprotein metabolism in men

Carbohydrate restricted diets (CRD) are popular for weight loss, and consistently reduce triglycerides (TG) and increase HDL-cholesterol (HDL-C); however, LDL-cholesterol (LDL-C) response is highly variable. Also, the mechanisms behind lipid changes and effects on emerging cardiovascular disease (CVD) risk factors are incompletely understood. The purpose of this dissertation project was to determine the effects of adding soluble fiber to a CRD on CVD risk and lipoprotein metabolism. ^ Using a parallel-arm, double blind, placebo controlled design, 30 men [body mass index (BMI) 25-35 k g/m2] were matched for BMI and age, then randomly assigned to consume either 3 g/d of glucomannan or placebo with a CRD for 12 weeks. Weighed food records were kept at baseline, and weeks one, six, and 12. Anthropometrics and blood measurements were completed at baseline, week six, and 12. ^ Compliance was excellent as assessed by diet records and ketonuria. Macronutrient composition was not different between groups. Energy distribution was 13:60:27 for carbohydrate, fat, and protein at week 12, and soluble fiber consumption was higher in the fiber group (P \u3c 0.05). Both groups experienced similar reductions in body weight and fat, waist circumference and plasma glucose (P \u3c 0.01). After 12 wk, HDL-C and TG improved significantly in the fiber (10 and -34%) and placebo (14, -43%) groups. ^ LDL-C decreased by 17.6% (P \u3c 0.01) at wk 6 and 14.1% (P \u3c 0.01) at wk 12 in the fiber group. Conversely, LDL-C reduction in the placebo group was only significant after 12 wk (-6.0%, P \u3c 0.05). Since no differences between groups existed in any measured plasma variable, data for all subjects were pooled and compared from baseline to week 12 for subsequent analyses. Apolipoproteins C-I (-13.8%), C-III (-21.2%) and E (-12.5%), VLDL particle number (-19%), and small LDL particles (-30%) were significantly reduced, while LDL particle size (2.5%), and large HDL particles (35.3%) increased. Lp(a) (-11.3%), C-reactive protein (-8.1%) and TNF-α (-9.3%) also decreased (P \u3c 0.05), while homocysteine remained unchanged. ^ Consumption of a CRD reduced CVD risk (particularly factors associated with metabolic syndrome), and improved lipoprotein metabolism, while soluble fiber supplementation provided no additional benefit.