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Insulin Resistance and the Cardiometabolic Syndrome: Adipose Tissue and Skeletal Muscle Factors

Weight regain after sustained weight reduction is accompanied by suppressed oxidation of dietary fat and adipocyte hyperplasia

¹University of Colorado Denver, Center for Human Nutrition; ²Department of Medicine, Division of Endocrinology, Diabetes and Metabolism; and ³Department of Pediatrics, Aurora, Colorado

Submitted 6 November 2007 ; accepted in final form 9 February 2008

A dual-tracer approach (dietary ¹⁴C-palmitate and intraperitoneal ³H-H₂O) was used to assess the trafficking of dietary fat and net retention of carbon in triglyceride depots during the first 24 h of weight regain. Obesity-prone male Wistar rats were allowed to mature under obesogenic conditions for 16 wk. One group was switched to ad libitum feeding of a low-fat diet for 10 wk (Obese group). The remaining rats were switched to an energy-restricted, low-fat diet for 10 wk that reduced body weight by 14% and were then assessed in energy balance (Reduced group), with free access to the low-fat diet (Relapse-Day1 group), or with a provision that induced a minor imbalance (+10 kcal) equivalent to that observed in obese rats (Gap-Matched group). Fat oxidation remained at a high, steady rate throughout the day in Obese rats, but was suppressed in Reduced, Gap-Matched, and Relapse-Day1 rats though 9, 18, and 24 h, respectively. The same caloric excess in Obese and Gap-Matched rats led to less fat oxidation over the day and greater trafficking of dietary fat to visceral depots in the latter. In addition to trafficking nutrients to storage, Relapse-Day1 rats had more small, presumably new, adipocytes at the end of 24 h. Dietary fat oxidation at 24 h was related to the phosphorylation of skeletal muscle acetyl-CoA carboxylase and fatty acid availability. These observations provide evidence of adaptations in the oxidation and trafficking of dietary fat that extend beyond the energy imbalance, which facilitate rapid, efficient regain during the relapse to obesity.

acetyl-CoA carboxylase; metabolic inflexibility; postobese; adipocyte cellularity

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