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1 Department of Pediatrics, University of Colorado Health Sciences Center, Denver 80262; 2 Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, Colorado 80525; and 3 Exercise Science Research Institute, Arizona State University, Tempe, Arizona 85287
Obesity results from
positive energy balance and, perhaps, abnormalities in lipid and
glycogen metabolism. The purpose of this study was to determine whether
differences in lipogenesis, retention of dietary fat, and/or
glycogenesis influenced susceptibility to dietary obesity. After 1 wk
of free access to a high-fat diet (HFD; 45% fat by energy) rats were
separated on the basis of 1 wk body weight gain into obesity-prone (OP;
48 g) or obesity-resistant groups (OR;
40 g). Rats were either
studied at this time (OR1, OP1) or continued on the HFD for an
additional 4 wk (OR5, OP5). Weight gain and energy intake were greater
(P
0.05) in OP vs. OR at both 1 (53 ± 2 vs. 34 ± 1 g; 892 ± 27 vs. 755 ± 14 kcal) and 5 (208 ± 7 vs. 170 ± 7 g; 4,484 ± 82 vs. 4,008 ± 72 kcal) wk, respectively. Rats were
injected with 3H2O and were either provided
free access to an HFD meal containing labeled fatty acids (fed;
n = 10 or 11/group) or were fasted (n = 10/group) overnight. The amount of food or 14C tracer eaten
overnight was equivalent between OP and OR rats. In liver, the fraction
of 3H retained in glycogen or lipid was not significantly
different between OR and OP groups. Retention of dietary fat in the
liver was not increased in OP rats. In adipose tissue, retention of 3H was ~49% greater (P
0.05) in OP1 vs.
OR1 and ~30% greater in OP5 vs. OR5, but retention of dietary fat
was not elevated in OP vs. OR. At the same time, fat pad weight (sum of
epididymal, retroperitoneal, mesenteric) was 49% greater in OP1 rats
vs. OR1 rats and 65% greater in OP5 vs. OR5 rats (P
0.05). Thus a greater capacity for lipogenesis or retention of dietary
fat does not appear to be included in the OP phenotype. The
characteristic increase in energy intake associated with OP rats
appears to be necessary and critical to accelerated weight and fat gain.
tritium; liver; adipose tissue; energy intake; high-fat diet
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