The Role of Exercise and Physical Activity in Weight Loss and Maintenance
Section snippets
Rationale for weight loss in overweight and obese patients
In the United States, 66.3% of adults are overweight or obese,1 which represents a major public health concern. The total medical cost associated with treating obesity exceeds $140 billion annually, and represents approximately 9.1% of annual medical expenditures.2 Obesity is a major risk factor for many cardiovascular (CV) diseases such as coronary heart disease (CHD), heart failure (HF), stroke, ventricular dysfunction, and cardiac arrhythmias.3 The American Heart Association's scientific
Physical activity and the prevention of weight gain
Changes in weight are affected by the amount of energy expended versus the amount of energy consumed.17 Therefore, if the energy expenditure remains low, but dietary consumption levels are in excess, weight gain will occur. Several researchers have argued that declines in PA both in occupational18 and leisure settings19 may have an important role in the increase in obesity rates over the last 30 + years. Furthermore, many epidemiological studies suggest that PA has an important role in weight
Weight loss from specific exercise programs in overweight and obese patients
In the following sections, we will discuss several different PA strategies for weight loss in obese patients and describe the overall likelihood for nominal and clinically significant weight loss. When possible, we have provided data from large randomized controlled trials to support our conclusions. Table 1 summarizes the expected weight change from different exercise training programs discussed in the following sections.
Pedometers to increase physical activity and promote weight loss
Pedometers are devices that count the number of steps that an individual accumulates throughout the day.25 The current consensus states that obtaining less than 5,000 steps per day is indicative of sedentary behavior, whereas greater than 8,000 or 10,000 steps suggests a more active lifestyle. Clinicians can utilize pedometers to assess a patient's current PA habits, and as a tool for patients to increase their PA levels. Pedometer-based interventions where sedentary participants increase PA
Weight loss from aerobic exercise at public health recommendation levels
Clinical trials of ET that report no weight loss or modest weight loss (< 5 kg) still report numerous health benefits for overweight and obese adults with risk factors for disease. These benefits include improving CRF,28., 29. glucose control,30., 31. endothelial function,32., 33. lipoprotein particle size,34 high density lipoprotein,35 and quality of life.36., 37. Weight loss as a result of aerobic ET is very heterogonous, and the overall response is related not only to total energy
Weight loss from high volume aerobic exercise training without caloric restriction
Current ACSM recommendations state that exercise programs need to exceed 225 min/wk in order to possibly induce clinically significant weight loss.15 Supervised ET studies which have demonstrated clinically significant weight loss with aerobic ET (without caloric restriction) have far exceeded the minimum levels of physical activity according to public health definitions.15 Ross et al.39 observed an 8% weight loss in obese men after 12 weeks of aerobic ET with no alterations in dietary habits
Weight compensation for aerobic exercise training
Individuals who lose less weight than expected based on their training energy expenditure have been termed “weight compensators.” Several studies have examined weight compensation after aerobic exercise training. King et al.41 observed increased energy intake and increased fat intake in weight compensators compared to those that did not compensate for weight loss. Using data from the DREW study, Church et al.16 examined weight compensation in postmenopausal women who were required to perform ET
Contributing effects of aerobic exercise intensity or resistance training on weight loss?
Vigorous intensity aerobic ET has been shown to have enhanced health benefits for important risk factors,42 including visceral fat,43 measures of glucose/insulin metabolism,44 and CRF,45., 46., 47. compared to moderate intensity aerobic ET. In terms of weight change, when different intensities of ET are matched for caloric expenditure or ET dose, both vigorous and moderate intensity aerobic ET result in similar amounts of weight loss. O’Donovan et al.47 in an RCT of 64 obese men observed
Is the weight loss achieved through caloric restriction enhanced by exercise training?
The literature is clear that caloric restriction is more likely to result in clinically significant weight loss compared to aerobic ET alone; however, the present literature is less clear if weight loss from caloric restriction is enhanced by adding ET/PA. Wing50 reported that, although ET and caloric restriction together may promote greater weight loss compared to caloric restriction alone, the differences in weight loss between groups were not statistically significant. Miller et al.51
Diet versus exercise induced weight loss
Another question that is often encountered in the clinical setting is if there is a difference between weight loss achieved through dietary means or through ET in terms of CV and T2DM risk factors. In an elegantly designed study, Ross et al.39 randomized obese men (n = 52) to diet-induced weight loss, exercise induced weight loss, exercise without weight loss, or a control group for 3 months. The diet-induced and exercise-induced weight loss groups lost approximately 7 kg of weight (8% weight
Exercise and weight maintenance
The ACSM position stand on PA intervention strategies to promote weight loss and weight regain15 emphasizes the distinction between the minimum levels of PA to maintain health (150 min/wk) and higher levels of PA to prevent weight regain (200 min/wk). Therefore, obese individuals who have successfully lost weight require a substantial amount of PA to maintain this weight loss. As indicated in the ACSM position stand,15 several major limitations to research of PA on weight regain exist including
The rationale for exercise within weight management programs
From the present literature, caloric restriction appears to have a more profound and consistent effect on weight loss compared to exercise training alone.51 Therefore, clinicians may be tempted to advocate the use of caloric restriction in weight management plans. Importantly, PA contributes to the negative energy balance seen with caloric restriction. From a clinical perspective, both CRF and PA levels are established independent risk factors for CVD, T2DM and all-cause mortality.10 Caloric
The obesity paradox
The only group where the clinical impact of weight loss may not be as clear is for individuals with established CV diseases. Recent evidence suggests that in individuals with CV disease, higher BMI levels are associated with better survival rates compared to those with lower levels.5 This phenomenon which has been termed “the obesity paradox” has been shown in a variety of CV conditions such as heart failure, hypertension, and coronary heart disease.5 Much of these data are epidemiological in
Conclusions
Exercise training, regardless of weight loss, provides numerous health benefits especially for overweight and obese individuals at risk for CV diseases or with current CV conditions. Although the weight loss from ET programs without caloric restriction are very heterogeneous, based on the present literature patients who engage in a PA program may experience modest weight loss(< 2 kg), but no weight loss is possible. Clinicians need to emphasize that substantial weight loss is unlikely to occur
Statement of Conflict of Interest
All authors declare that there are no conflicts of interest.
Acknowledgments
Supported in part by an NIDDK T-32 fellowship (Obesity from Genes to Man, T32 DK064584-06).
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Statement of Conflict of Interest: see page 446.