Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Human Ecology

First Advisor

Michael Keenan


Introduction. A high amount of dietary fat has been shown to have a negative effect on metabolism, causing insulin resistance, weight gain, and other metabolic alterations. Several studies have found a direct link between lack of activity and obesity. Purpose. The purpose of this study was to see if a diet had an effects on insulin sensitivity, autonomic nervous system function, and substrate utilization as predicted by Flatt, in healthy young men. Subjects. The subjects studied were 6 nonathletes (NA), 6 aerobically trained (AT), and 5 weight trained (WT) men. Their body mass index (BMI) was 22.1 $\pm$ 2.92 kg/m$\sp2$ (mean $\pm$ SD), age 22.5 $\pm$ 5.01 yr, and body fat 15.9 $\pm$ 6.5%. The study was a crossover design with a high (HF 50%) or low (LF 20%) fat diet assigned randomly for 7 days after 5 days of control diet (40% fat). Results. Energy expenditure (EE) was highest in the WT subjects, but after correcting for LBM, NA had the highest energy expenditure. Diet had an overwhelming effect on substrate oxidation and RQ. During an early overfeeding period, fat oxidation was reduced, while carbohydrate oxidation increased, but these shifted to accommodate intake on both HF and LF diets when energy balance was zero. Fat oxidation was significantly higher on the HF diet than on the LF diet but there was no significant difference by groups. Insulin sensitivity and glucose effectiveness were significantly higher on the LF than on the HF diet. There was no significant difference in cardiac autonomic activity by groups or diets. Resting catecholamine excretion was significantly higher on the HF diet. Additionally, using LBM as a covariate resulted in significant differences among groups in 24-hour and resting epinephrine excretion on the HF diet. Conclusions. The results indicate that S$\sb2$ appears to function as indicated by causing an increased carbohydrate oxidation during overfeeding. When energy and carbohydrate balances were below S$\sb2$: fat oxidation increased, carbohydrates were spared, even a HC diet did not fill S$\sb2$ at zero energy balance. A hierarchy of importance in relation to weight gain and weight maintenance are (1) overfeeding, (2) exercise, (3) high or low fat diets.