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Exercise induces negative energy balance either directly or by enhancing meal thermogenesis, increasing resting metabolic rate, and/or decreasing food intake. A quantitative evaluation of these effects in programs of weight control led to the following conclusions: 1) energy cost of exercise per se is minimal, 2) effects on thermic of food are negligible, and 3) exercise training may be advantageous in conjunction with low-calorie diet programs because it helps to maintain resting metabolic rate and fat-free mass. However, exercise may not prevent, and may even accentuate, the fall in metabolic rate in programs of severe calorie restriction, thus hampering weight reduction. Overall, exercise should not be envisioned as a sole agent to induce negative energy balance, but it is an essential element in comprehensive programs for morbidly obese patients due to its effects on lipids, carbohydrate metabolism, and cardiovascular system.

The postexercise recovery period is characterized by transition from the acutely catabolic phase that occurs during exercise to an anabolic phase. Muscle glycogen stores are replenished after exercise and even in the absence of refeeding have returned to 50% of preexercise concentrations within 12 h (1). The increase in net protein degradation that is demonstrable during exercise at low-to-moderate workboads is replaced by net protein resynthesis as soon as exercise is stopped (2, 3). These anabobic responses are essential for physical training to result in increased glycogen stores and lean body mass. Physical training programs have been advocated as an important component in the treatment of subjects with noninsulin-dependent diabetes mellitus (NIDDM). Physical training was shown to improve the major defect present in NIDDM, ie, peripheral insulin resistance (4), and to improve glycemic control in these subjects (5). How much ofthis beneficial effect ofregular physical exercise is due to the cumulative effects of single bouts of exercise vs a specific training effect has been unclear. Recent work suggests that benefits may be demonstrable after single bouts ofexercise (6, 7) and the training effect is rapidly lost when an exercise program is interrupted (7, 8). Although most exercise studies have focused on effects on peripheral (skeletal muscle) insulin sensitivity, hepatic glucose production may also be affected by exercise(6). Although postexercise recovery is characterized by overall anabobic responses, these responses may vary in different body compartments. Ahlborg et al (9) showed that nonexercised muscle demonstrates ongoing catabolism (glycogenolysis) during the early postexercise period (40 mm) with release ofbactate presumably for gluconeogenesis. Whether this differential response (catabolism in nonexercised muscle, anabolism in exercised muscle) occurs for longer periods and involves other gluconeogenic precursors requires further study. Finally, food ingestion during exercise was shown to enhance endurance exercise performance in some studies ( 10) but not in others ( 11). Preexercise glucose ingestion may adversely affect performance (1 2). We (13) studied the effects of preexercise ingestion of a mixedmeal snack on the metabolic fuel responses during and after exercise. Subjects for the studies conducted during the bate (1216 h) postexercise recovery period consisted of six male control subjects within 18% of ideal body weight (14), designated as lean for the purpose of the study; six male subjects > 130% ideal body weight with either glucose intolerance or hyperinsubinemia during a 75-g oral glucose tolerance test ( 15), designated as obese; and five male subjects with NIDDM (1 5) who were all > 1 18% ideal body weight. Subjects for the studies conducted during early (2-4 h) postexercise recovery consisted of 1 1 lean healthy subjects (6 male, 5 female). For the studies of the effects of preexercise snack feeding, nine healthy male subjects within 15% of ideal body weight were selected. Except for obesity and diabetes melbitus in the respective groups, all subjects were deemed to be in excellent health as determined by medical history, physicab examination, and laboratory screening chemistry studies.

A population sample of 142 men and 148 women aged 40-69 was drawn in Chittenden County, Vermont, and studied for interrelationships among several parameters of obesity, fasting serum cholesterol, triglycerides, glucose and insulin concentrations, and 2-hour post-Glucola glucose and insulin concentrations. No significant sex differences were observed with regard to mean fasting concentrations of glucose, insulin, cholesterol, or triglyceride. Post-Glucola insulin concentrations were higher in women, particularly in the older age groups. Positive correlations were observed between mean log fasting insulin concentration and all parameters of obesity except log triceps skinfold thickness in men. In addition, a positive correlation was present between mean log fasting insulin and fasting triglycerides. There was a positive correlation between fasting triglycerides and ponderal index and estimated percent body fat. Fasting triglycerides correlated with percent ideal weight in women but not in men and with log subscapular skinfold thickness in men but not in women. There was no correlation with either log triceps skinfold thickness or with combined triceps and subscapular skinfold thickness in either men or women. No positive correlations were observed with regard to serum cholesterol. The measurement of glucose and insulin concentrations 2 hours post-Glucola or the calculation of insulin-to-glucose ratios did not provide additional correlations to those observed from the fasting data alone and in some instances correlations which existed in the fasting state were largely obscured following carbohydrate administration.

We studied the effects of prior high-intensity cycle exercise (85% VO2 max) on total energy expenditure (EE) and the thermic effect of insulin (TEI) in normal controls and in obese insulin-resistant and noninsulin-dependent diabetic (NIDDM) subjects. Normal controls, but not obese or NIDDM subjects, showed a significant increase (3-7%) in total EE 12-16 h after exercise (p less than 0.05). Prior exercise increased lipid and decreased glucose oxidation in all groups. During low-dose insulin infusion (40 mU X M2 X min), prior exercise potentiated TEI in control and NIDDM subjects (p less than 0.05), whereas obese subjects showed no response. During high-dose insulin infusion (400 mU X M2 X min), TEI was similar in NIDDM and control subjects but was significantly less in the obese group. In this study, we found a positive correlation between TEI and insulin-stimulated rates of glucose disposal (r = 0.91, p less than 0.001). The predicted cost of glucose storage accounted for 42% of TEI.

28%. The energy cost of protein synthesis and degradation is also high, requiring ap­ proximately 24% of the available energy in amino acids, whereas the cost of storage and remobilization of dietary fat is only about 7% (I). External factors that regulate nutrient in­ take include availability, preparation and palatability of foods, social setting and pres­ sures, and a variety of environmental con­ ditions such as heat or cold exposure. Energy stores The measurement of body energy stores is also important in studies of energy bal­ ance, because small changes in body com­ position may mask significant differences in energy intake or expenditure. Changes in body weight are often used to indicate posi­ tive or negative energy balance, but these may be misleading when concomitant changes in body composition are not known. Measurements of body fat content and fat­ free mass provide much more useful data and can be made by a variety oftechniques, the most accurate of which are estimation ofbody fat from body density measurements or estimation of lean body mass from meas­ urements of total body water or 40K con­ tent. Each ofthese methods involves the use of formulae which carry one or more as­ sumptions regarding body composition. However, in general they give comparable results and are most accurate in the mid­ range of body composition with greater er­ rors at the extremes. Several other, less tech