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Abstract
The objective of this dissertation was to determine the effect of feeding monosaccharides and fat on the development of leptin resistance, feed intake, growth, and metabolism in the rat and pig. Three rat experiments were completed to determine if feeding glucose, fructose, or starch with or without fat could alter leptin responsiveness in a short period (experiment 1 and 3) and over a long period (experiment 2). Rats fed the high-fat fructose diet increased energy expenditure after leptin treatment, compared to the rats fed the high-fat glucose fed diet where the increase in energy expenditure was limited. However, over a long period of time, the carbohydrate source in the diet alters central leptin resistance. The rats fed the glucose diet decreased intake after the central leptin injection. The starch and fructose fed rats were leptin resistant. Two experiments were conducted to determine if the source of dietary carbohydrate, with or without added fat, had an effect on body weight gain, glucose metabolism, or insulin response in growing pigs. Pigs were fed four diets: 1) 20% starch; 2) 10% glucose + 10% starch; 3) 10% fructose + 10% starch; or 4) 20% fructose for 9 weeks. There was a main effect of dietary fat to reduce feed intake. Serum fructose concentrations after the RTM test were elevated in pigs fed fructose diets. In the second experiment pigs were fed six diets: 1) 20% starch; 2) 10% glucose + 10% starch; 3) 10% fructose + 10% starch; and 4) 20% fructose for 9 weeks. Compared to the other dietary treatments, pigs fed fructose with high fat had an elevated glucose area under the curve during the GTT. It is likely that studies of longer duration are needed to determine if these changes are indicative of insulin resistance. The work demonstrates that pigs are a viable model to test the long-term effects of dietary carbohydrates on metabolism and body composition.