Dietary obesity in rats: influence on carbohydrate metabolism.

When male rats were fed a high diet from 3 to 20 weeks of age, they weighed 633 g which was 30% more than the animals fed a high glucose diet. Blood samples after a 16 to 18 hour fast, from the rats fed the high fat and high glucose diets contained, respectively: 130 +/- 11, 110 +/- 8 mg glucose/100 ml; 27 +/- 5, 24 +/- 3 microunits immunoreactive insulin (IRI)/ml; 791 +/- 58, 1104 +/- 179 meq nonesterified fatty acids (NEFA)/L. A tolerance test, by stomach tube, with 125 mg of glucose/100g body weight indicated that the rats fed the high fat diet had significantly higher mean plasma glucose concentrations, lower IRI responses and a lower leve of NEFA than rats fed a high glucose diet. Switching diets for 5 weeks resulted in body weights of about 600 g for both groups of rats. Those rats switched from the high fat to the high glucose diet did show an improved glucose tolerance, while the reverse was true of rats switched from the high carbohydrate to the high fat diet.