Effects of a structured lipid, Captex, and a protein-based fat replacer, Simplesse, on energy metabolism, body weight, and serum lipids in lean and obese Zucker rats

The effects of a structured lipid, Captex 810D, and a protein based fat replacer, Simplesse, on the energy metabolism of 8-week-old female lean and obese Zucker rats were measured for 14 days. Body weight gain and serum lipids and glucose were also measured after 4 weeks on the experimental diets. Zucker rats were divided into six groups (n = 9) as follows: lean control (LC), obese control (OC), lean Captex (LX), obese Captex (OX), lean Simplesse (LS), and obese Simplesse (OS). Heat production was measured using open circuit respiration chambers (Oxymax animal calorimeters). Average dry matter (DM) intake (g/kg0.75/d) during the respiration trials (two 24-hour periods) was significantly less (P < 0.05) in the OX and OC groups than in the OS group (31.9 +/- 1.6 and 33.1 +/- 1.5 SE, respectively, vs 40.1 +/- 4.2 SE). Gross energy (GE) was 5.2 and 4.7 kcal/g DM for the control and the Captex diets, respectively. Metabolizable energy density (ME, kcal/g DM) for Simplesse diets were significantly different from the ME in the control and Captex diets. ME density was less in the OS due to greater urine energy excretion (polyuria) in that group. ME intake (kcal/kg0.75/d) was similar for all groups (169.0 +/- 4.0 SE) when expressed on a metabolic body size basis, with the intake of the OX being 163.8 +/- 6.9 SE. Heat production or energy expenditure (kcal/kg0.75/d) of the OX group was significantly higher than the OC group (85.2 +/- 2.8 SE vs 76.0 +/- 2.9 SE), but the OC group was not significantly different from the OS group (76.9 +/- 2.9 SE). Experimental diets did not affect heat production in lean rats. A phenotypic effect was observed in serum glucose, triglycerides, cholesterol, and high density lipoprotein (HDL) cholesterol concentrations between lean and obese rats. Obese rats consuming the Simplesse diet had significantly lower glucose concentrations than the Captex and the corn oil control groups (16.3 +/- 3.8 vs. 20.1 +/- 4.8 and 20.7 +/- 2.1 mmol/L, respectively). Serum triglycerides (5.61 +/- 0.55 mmol/L vs. 4.27 +/- 0.81 and 4.21 +/- 0.91 mmol/L) and total cholesterol concentrations (3.96 +/- 1.09 mmol/L vs. 3.18 +/- 0.49 and 3.33 +/- 0.51 mmol/L) in the obese rats on the Simplesse diet were greater than the Captex and the control groups. Obese rats had higher HDL cholesterol concentrations than the lean rats but no difference due to diet was observed in either rats.