The combination of exercise and diet has long been prescribed for severe obesity. Support for this rational comes from reports of the effects of strenuous exercise and physical training in the non-obese, sedentary, athletic, and those with only mild or moderate degrees of obesity. Relatively fewer studies have been conducted with severe or morbid obese subjects (23).
Exercise alone is probably insufficient to bring about significant fat loss except in individuals who are extremely motivated. The combination of modest caloric restriction and physical training may be necessary to induce favorable changes in body composition (27). Although prolonged, intense physical exercise may promote weight loss, more moderate exercise, as practiced by non-athletes may not induce significant weight loss. In some cases, weight gain has actually been reported (28, 29). The combination of modest caloric restriction and physical training may be necessary to induce favorable changes in body composition (27).
In a landmark study in 1976, Zuti & Golding compared changes in body composition in three treatment groups. In group one, each subject reduced dietary intake by 500 Calories daily. Group two increased energy expenditure by 500 Calories daily. Group three combined a dietary restriction of 250 Calories and an energy expenditure of an additional 250 Calories. Through the 16 week study, all groups lost comparable weight, 11.7 lbs., 10.6 lbs., and 12 lbs. respectively. The exercise and combination groups lost more fat, 9.3 lbs., 12.6 lbs., and 13 lbs. respectively. Group one experienced a loss of muscle mass while the group two gained the greatest muscle mass, -2.4 lbs., 2 lbs., and 1 lb. respectively (30).
Regular exercise tends to preserve lean body mass even with caloric restriction (31). Van Loan, M. D. et al. evaluated the effects of endurance exercise on fat-free mass and nitrogen balance, with energy restriction or with energy intake to meet non-exercise needs in obese women. Endurance exercise had a slower rate of weight loss and a lower loss of fat free mass than the diet and exercise group. Nitrogen balance was more positive in the endurance exercise group than the diet and exercise group. Although, changes in fat free mass, assessed by nitrogen balance, were different from the results obtained by total body electrical conductivity. This difference suggests decreased FFM were due to fluid losses, which were confirmed by deuterium dilution procedures. This study demonstrates that body protein stores may be maintained during periods of endurance exercise and dietary restriction in obese women (32).
The major fraction of daily energy expenditure in the obese comes from their resting metabolism, although exercise can contribute to a substantial portion (33). Lean body mass retention tends to maintain resting metabolic rate. Among other factors, lean body mass is related to resting metabolic rate (34). Shinkai, S., et al. concluded aerobic exercise enhances the effect of moderate dietary restriction by augmenting the metabolic activity of lean tissue in mildly obese middle-aged women (35).
The combination of moderate energy restriction and either resistance or aerobic exercise induces significant reductions in visceral and subcutaneous adipose tissue and are thus effective means of reducing total and upper-body obesity in obese women (36). The American College of Sports Medicine's Guidelines for Exercise Testing and Prescription asserts that both weight training and aerobics can contribute to a loss of fat, yet they claim aerobic exercise is more efficient because it involves a sustained, high rate of energy expenditure (4). Weight training seems to be superior in preserving or increasing fat-free mass during a calorie restrictive diet (37) and increasing functional strength.
In 1988, Ballor, D. L. et al. assessed the effects of weight training on body composition in an 8 week weight loss study. Forty obese women were randomly assigned to one of four groups: diet without exercise; diet plus weight training; and weight training without diet. The authors concluded that caloric restriction diet supplemented with a resistive weight training program results in maintenance of lean body weight compared with dieting alone. Furthermore, they found that weight training resulted in comparable gains in muscle area and strength in both weight training groups; with and without diet (38).
In 1989, Walberg, J. L. commented on the value of weight training in the treatment of obesity. He noted that resistance exercise appeared to prevent the loss of or even increase in muscle mass during energy restriction. Walberg argued that resistance exercise is less likely than aerobic exercise to acutely increase lipid and energy utilization but may indirectly aid weight reduction by increasing lean tissue and metabolic rate. He concluded that the value of aerobic exercise during weight loss was apparent, but the potential of resistance exercise in weight remained unclear (39).
Donnelly, J. E. et al. (1991), studied the benefits of aerobic exercise and weight training combined with a very low calorie diet. He discovered that changes in body weight, percent fat, fat weight, and fat-free mass, were not different between exercise/diet groups and diet groups. All groups exhibited declines in resting metabolic rate. This study failed to show advantages of any exercise regimen over diet alone for weight loss, body-composition changes, or declines in resting metabolic rate, although limited improvements in work capacity were reported in the exercise groups. Conversely, strength improvements were found in the exercise groups that included strength training (40).
It should be noted that exercise is less likely to induce changes in resting oxygen uptake, adipose, and water weight when combining severe dietary restriction than those employing moderate dietary restrictions (41). Likewise, Dengel, D. R., et al. concluded that in older, obese men, hypocaloric dieting combined with aerobic exercise training does not attenuate the loss in fat-free mass that occurs during weight loss by hypocaloric dieting alone (42).
Conversely, Sweeney, M. E. et al. found that moderate calorie restriction (70%) may offer an advantage over severe energy restriction (30%) because it produces a greater energy loss relative to energy deficit. Although women in the severe energy restriction group lost more weight (mean +/- SE: 15.1 +/- 1.4 verses 10.8 +/- 1.0 kg.), fat (11.7 +/- 1.1 verses 8.3 +/- 0.6 kg.), and fat-free mass (2.8 +/- 0.3 verses 1.8 +/- 0.3 kg.) than the moderate calorie restriction group (P < or = 0.05). The overall energy loss relative to energy deficit was greater in the moderate calorie restriction group (0.80 +/- 0.07) compared with the severe energy restriction group (0.52 +/- 0.05; P < or = 0.01). Conversely, exercise had no significant effect on energy loss relative to energy deficit (43).
Physical training has been valued in the treatment of obesity for elevating mood, reducing hunger, and improving the likelihood of a successful outcome (44). Holm et. al. reported a temporary suppression of the appetite after the initial bouts of a conditioning program (45).
Caloric intake does not seem to change in proportion to energy expenditure during inactivity or exhaustive work. Yet, within these extremes, caloric intake does seem to change in accordance to the demands of energy expenditure (46). Staten found that men increased their intake by 200 Calories per day when subjected to 5 days of exercise (1 hour at 70% Vo2 max) whereas women did not (47).
Exercise can result in health and fitness benefits in the obese independent of weight loss. An increase of fitness can decrease the risk of cardiovascular disease and type 2 diabetes, even if no weight loss is observed.
Strenuous exercise and physical training can improve insulin sensitivity (12, 48). Interestingly, athletes and well-trained people possess a more efficient insulin-mediated glucose uptake than their sedentary counterparts (29). The addition of exercise to a low-calorie diet may prevent glucose tolerance impairment which seems to be associated with dieting alone (24). Regular intense and prolonged exercise can significantly lower plasma insulin concentrations with little effect on glucose tolerance. This effect has been attributed to improved insulin sensitivity and occurs with or without an accompanying body fat reduction (49). Although, it appears the effects of physical training on insulin sensitivity may be related to exercise's effects on adiposity (50, 48).
Tremblay, A. et al. conducted a study to evaluate the additive effect of exercise and a low fat diet on body weight, body composition, and metabolic profile in obese women. At the conclusion of the study, the subjects were still overweight, but their plasma glucose and insulin during an oral glucose tolerance test were similar to values obtained in a sample non-obese women. Furthermore, plasma lipid and lipoprotein levels were found to be normal with the exception of plasma apo B and HDL-C levels. The researchers concluded that aerobic exercise training and a low fat diet can normalize the metabolic profile of obese women, even if their adiposity remains higher than that of lean women (51).
Weight loss and fat reduction can decrease arterial pressure, lower plasma triglyceride and cholesterol concentrations, and can result in cardiovascular improvements (52). Likewise, regular exercise can lower plasma triglyceride levels in obese individuals. It is still unclear whether this change is due to the effects of regular exercise on metabolism or because of weight loss (53). In overweight women, regular exercise has been shown to slightly reduce hypertension, even with no or only slight weight reduction (54).
A multifaceted weight reduction program, including diet, exercise and behavior modification, has been shown to be more effective than other weight reduction programs (55). An increase of calorie expenditure is the major goal in prescribing weight loss programs. A balance between intensity and duration should be manipulated to yield a high total caloric expenditure. Approximately, 300 to 500 Calories each bout and 1000 to 2000 Calories per week for adults is recommended. Since many obese individuals are at an increased risk for orthopedic injury, nonweight-bearing activities may initially be recommended. Likewise, a variation of exercise modes and modifications in frequency and duration may be required. An intensity of 60% or less of functional capacity or maximal heart rate may be maintained to improve cardiorespiratory endurance (4). Although weight loss through exercise and modest calorie restriction is slow, the likelihood of achieving successful weight maintenance is greatly enhanced through physical activity.