Resistance to diet-induced obesity: food intake, pancreatic sympathetic tone, and insulin.

After 15 wk on a moderately high-calorie high-fat (CM) diet, 43% of 40 3-mo-old male Sprague-Dawley rats developed diet-induced obesity (DIO) (29% more weight gain), whereas 57% of diet-resistant (DR) rats gained no more weight than 20 chow-fed controls. When switched to chow for another 7 wk, DR rats ate 13% less, gained 55% less weight, and had 49% lower food efficiency, whereas DIO rats ate 4% less but had comparable weight gain and efficiency to controls. DIO rats had 29% more carcass lipid (percent of carcass weight). DIO rat retroperitoneal white adipose pads had 65% more cells that were the same size as those in chow-fed pads; DR rat cells were similar to controls. Both DR and DIO rats increased norepinephrine turnover in their interscapular brown adipose pads by greater than 90%. DIO rats also had 40% lower pancreatic turnover; their plasma insulin levels were 327% of controls after 15 wk on the CM diet and 188% after 7 wk on chow. DR levels were the same as controls at both times. Therefore, regulation of caloric intake, pancreatic sympathetic tone, and plasma insulin levels were three important differences between rats that resisted and those that developed DIO on high-energy diets.