Objectives: Low-carbohydrate diets very high in total and saturated fat may, despite possible weight-loss advantages, increase cardiometabolic risk. In this randomized controlled trial, we sought to determine macronutrient-specific effects on ectopic fat deposition and circulating risk markers, with particular attention to possible differences in short-term responses.
Methods: Forty-six abdominally obese men were randomized to either a very-high-fat low-carbohydrate (VHFLC) or low-fat high-carbohydrate (LFHC) diet for 12 wk. The diets were isocaloric, provided equal protein and PUFAs, and emphasized low-processed foods without added sugar. Dietary intake based on food weighing was recorded each month for 5 consecutive d. Blood samples were collected at baseline and after 4, 8, and 12 wk. Changes in body composition were quantified by bioelectrical impedance and CT.
Results: Recorded intakes of carbohydrate, total and saturated fat in the VHFLC/LFHC groups were 11/51, 71/29, and 34/12 energy percent, respectively. Both diets similarly reduced body weight, visceral fat mass, hepatic lipid content and circulating concentrations of TAG, insulin and HbA1c, and HOMA-IR (all p < 0.01). Diet-dependent responses were observed for total and LDL cholesterol (decreased only on LFHC) and HDL cholesterol (increased only on VHFLC). Non-esterified fatty acids (NEFA) increased on both diets from baseline to 4 and 8 wk, and returned to baseline levels after 12 wk. All biochemical variables improved significantly from 8 to 12 wk on the VHFLC diet, in contrast to a more gradual response in the LFHC group.
Conclusions: Both diets led to significant improvements in body composition and circulating risk factors, but with different temporal changes. Our data do not support that dietary fat per se promotes ectopic adiposity and cardiometabolic syndrome in humans.
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