The Role of Exercise and Physical Activity in Weight Loss and Maintenance

Abstract

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), heat failure (HF), stroke, ventricular dysfunction, and cardiac arrhythmias ³. The American Heart Association's scientific statement on obesity and weight loss ³ recommends weight loss in overweight and obese patients to reduce the severity of CV risk factors. Weight loss in these patients have been associated with improvements in many cardiometabolic risk factors such as prevalence of the metabolic syndrome, insulin resistance, type 2 diabetes (T2DM), dyslipidemia, hypertension, pulmonary disease, CV disease, and inflammation ³. Clinically significant weight loss (≥ 5% of baseline body weight) has been shown to be more effective in reducing CV and T2DM risk factors ⁴. Thus, a strong rationale exists for clinicians to advocate that overweight and obese patients attempt at least modest weight loss. Recent epidemiological evidence has emerged showing greater survival in adults with CV diseases with higher obesity levels compared to lower levels, which has been coined “the obesity paradox” ⁵. Although, the findings of the obesity paradox have been verified in several studies within different clinical populations^6-8, at the present time, little evidence exists that lower survival is observed in adults with CV diseases after modest or clinically significant weight loss.

High physical activity (PA) levels or exercise training (ET) should be an integral part of any treatment plan for obese individuals regardless of weight loss goals, and is associated with numerous CV benefits ⁹. High levels of PA and cardiorespiratory fitness (CRF) are inversely associated with CV disease, T2DM and all-cause mortality ¹⁰. Several epidemiological studies even suggest that high levels of PA or CRF attenuates the health risk of obesity ^11-13. Moreover, CRF levels have been shown to alter the relationship of the obesity paradox ¹⁴, where high CRF level is associated with greater survival in all body mass index (BMI) categories. So above all, clinicians should always encourage their patients to adhere to ET programs or engage in regular PA regardless of the weight loss achieved.

The present American College of Sports Medicine (ACSM) recommendations for physical activity to maintain health ⁹ and promote weight loss ¹⁵ are summarized in Figure 1. Strong evidence exists that PA can attenuate weight gain in those at risk for obesity, and many ET programs are capable of producing at least modest weight loss (~2 kg) ¹⁵. A question often encountered in the clinical setting from patients is how much exercise is needed to lose weight and what type of ET should be performed. Overall, the changes in weight in response to ET without caloric restriction are highly heterogeneous and individual differences can span weight gain to clinically significant weight loss ¹⁶. Clinicians should consult their patients on what are reasonable expectations based on their specific weight loss program. In the following paper, we will discuss the role of PA and ET in the prevention of weight gain, the expected weight loss from different ET types/modalities, how much PA is necessary to reduce recidivism following weight loss, and further discuss the obesity paradox.

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Figure 1

Current recommendations for amounts of physical activity based on goals for maintaining health, prevention of weight gain, promoting clinically significant weight loss, and prevention of weight gain after successful weight loss. Recommendations are based on the American College of Sports Medicine position stand of Appropriate Physical Activity Intervention Strategies for Weight Loss and Prevention of Weight Regain for Adults.

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 occupational ¹⁸ and leisure settings ¹⁹ 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 gain ^15,19-21. Williamson et al. ²² using data from the National Health and Nutrition Examination Survey observed that low levels of self-reported recreational PA was associated with a 3-fold greater risk of major weight gain in men and almost a 4-fold in women. In a prospective study of 34,079 middle aged women (mean: 52.2 yrs), Lee et al. ²⁰ observed that in women the risk of weight gain over a three year period was 11% greater in women who participated in less than 7.5 metabolic equivalent (MET)·hr/wk compared to women who participated in greater than 21 MET·hr/wk (approximately 300 minutes/week of moderate PA). Several studies using the Aerobic Center Longitudinal Study database have observed that CRF level ²³, PA level ²⁴, and change in PA level ²⁴ are inversely associated with future weight gain. Clearly, PA and CRF levels have an important role in weight gain for those at risk.

Researchers have speculated on the amount of PA necessary to prevent weight gain^15,21. The ACSM position stand ¹⁵ recommends 150-250 minutes per week of moderate to vigorous PA, with an energy equivalent of 1,200 to 2,000 kcals per week. Saris et al. ²¹ recommended that PA levels of 225 to 300 minutes per week were necessary to prevent the transition of normal weight to overweight or overweight to obese. Thus, clinicians should always recommend that patients engage in regular ET even if they are normal weight, and certainly if they are at risk for becoming overweight or obese.

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 levels to 10,000 steps or 2000-4,000 step/day above baseline levels have shown some positive effects for weight loss; however, in general weight loss tends to very modest (<2 kg) ^25,26. Richardson et al. ²⁷ performed a meta-analysis on pedometer-based interventions without caloric restriction (median duration: 16 weeks), and observed that pooled estimated change in weight was −1.3 kg. Bravata et al. ²⁶ performed a meta-analysis regarding the physiological effects of pedometer-based interventions on risk factors for CV disease, and has observed significant reductions in BMI (−0.38 kg/m²), systolic blood pressure (−3.8 mmHg), diastolic blood pressure (−0.3 mmHg), but no significant reduction in cholesterol, triglyceride, or fasting glucose levels. Although, asking a participant to walk a certain amount of steps can promote favorable changes in CV disease risk factors and may provide minimal weight loss, little empirical evidence exists that a pedometer-based program alone without caloric restriction can promote clinically significant weight loss.

Weight Loss from Aerobic Exercise at Public Health recommendation levels

Clinical trials of ET that report no weight loss or modest weight loss (<5 kgs) 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 lipoprotiein 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 expenditure, but also compensatory changes in dietary caloric intake ¹⁷. Large randomized controlled trials (RCTs) which have evaluated the change in weight following aerobic ET programs consistent with PA recommendations have observed either no changes in weight or only modest weight loss.

The following studies represent the strongest research design to evaluate changes in weight from aerobic ET as they have a large sample size of overweight or obese individuals at baseline, supervised ET sessions, strong adherence to their aerobic ET program, and comparison of weight change against a control group. The Dose Response to Exercise in Women (DREW) study ²⁸ (n=464) observed no significant changes in body weight in postmenopausal women exercising at 50% (−0.4 kg), 100% (−2.2 kg) and 150% (−0.6 kg) of public health guidelines for 6 months despite greater than 89% adherence in all ET groups. The Inflammation and Exercise (INFLAME) study (n=129) ³⁸ observed no significant change in body weight (−0.4 kg) compared to the control group (0.1 kg) after 4 months of ET in adults with elevated C-reactive protein levels at baseline. The Studies of a Targeted Risk Reduction Intervention through Defined Exercise (STRRIDE) study ³⁴ (n=84) observed significant, but minimal weight loss in those exercising at low amount/moderate intensity (−0.6 kg, 176 min/week), low amount/high intensity (−0.2 kg, 117 min/week ), or high amount high intensity (−1.5 kg, 171 minutes/week) following 6 months of aerobic ET. The Diabetes Aerobic and Resistance Exercise (DARE) study ³¹ (n= 251) observed significant weight loss in the aerobic ET group (−0.74 kg) compared to the control group after 22 weeks of intervention in adults with T2DM.

Thus, overweight and obese adults who adhere to an exercise program consistent with public health recommendations without a dietary plan involving caloric restriction can expect to experience weight loss in a range of no weight loss to approximately 2 kgs. Clinicians should caution their patients that the chances of substantial weight loss are unlikely at these ET levels without caloric restriction ¹⁵. Regardless of the amount of weight loss, clinicians should emphasize that numerous health benefits occur in the absence of weight loss, and that maintenance of an active lifestyle will reduce the risk of future weight gain ^15,19. An important limitation of the present data in this area is that long-term (> 1 year) and time-course studies are not currently available.

Weight loss from high volume aerobic exercise training without caloric restriction

Current ACSM recommendations state that exercise programs need to exceed 225 min/per week 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(daily exercise sessions of 700 kcals). In a different study, Ross et al. ⁴⁰ observed an 6.8% weight loss in premenopausal women (BMI>27) following 14 weeks of aerobic ET with an energy expenditure of 500 kcals per session. In the Midwest Exercise Trial, Donnelly et al. (n=131) observed a 5.3% weight loss in men after 16 weeks of aerobic ET at approximately 2,000 kcals per week. In contrast, the women in the exercise group did not have a significant change in weight (0.7 kg) following the intervention, but the exercise program prevented the weight gain observed in the control group (2.9 kg.) Thus, clinically significant weight loss is possible with aerobic ET without caloric restriction, but it requires a high ET volume. For the general population, these ET volumes may not be practical or sustainable.

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 at 50%, 100% and 150% of public health recommendations, and restricted the analysis to those who were 85% compliant to exercise training. The authors observed that the most weight compensation (less weight loss achieved than predicted from ET alone) occurred in the women exercising at 150% of the recommended volume. In fact, the amount of actual weight loss achieved in women exercising at 50% (−1.4 kg) and 150% (−1.5 kg) of the PA recommendations were virtually identical to each other despite the greater level of energy weekly energy expenditure in the 150% group.¹⁶. Thomas et al. ¹⁷ performed an analysis of weight change from 15 aerobic ET interventions, and concluded that the major factors limiting the expected weight loss from aerobic ET were dietary compensation and low aerobic ET dose. At the present time, evidence is limited to explain whether other factors of the energy balance equation, including compensatory changes in non-exercise PA (except for perhaps older adults), resting metabolic rate, movement efficiency, or changes in lean mass, are responsible for weight compensation with 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 ^45-47, 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 similar changes in weight following 6 months of moderate intensity (−1.1 kg) and high intensity (−0.5 kg) aerobic ET. In the STRRIDE study, Kraus et al. ³⁴ observed similar weight loss in overweight/obese adults participating in 8 months of moderate (−0.6 kg) and high intensity (−0.2 kg) aerobic ET at the same exercise dose (14 kilocalories per kg per week). Vigorous intensity aerobic ET can contribute to greater weight loss if matched for session time compared to moderate intensity aerobic ET because the total energy expenditure is greater. Thus, if vigorous aerobic ET can be sustained and is enjoyable for the patient, the exercise program may induce additional health benefits and potentially increase the energy expenditure seen with exercise training (if replacing the exercise time of moderate intensity training).

Resistance ET and isometric exercises are important and sometimes overlooked aspects of an ET program that have many health benefits including increasing/maintaining muscular strength with aging (prevention of sarcopenia) and preserving bone mineral density^9,48. Although, resistance ET alone contributes to the reduction of body fat, the effect on overall weight loss is minimal ¹⁵. In the Health Benefits of Aerobic and Resistance Training (HART-D) study, Church et al. ³⁰ observed no significant change (−0.3 kg) in weight in the resistance ET group (n=73) compared to a control group after the 9 month intervention. In the DARE trial ³¹, no significant difference was observed between the resistance ET group and the control group (0.3 kg). Bateman et al. (n= 86) observed no significant change in weight (0.07 kg) following 8 months of intervention in the STRIDDE AT/RT study ⁴⁹. Overall, little evidence exists that resistance training alone promotes weight loss.

Very few randomized controlled trials have explored whether the combination of both aerobic and resistance ET leads to a greater reduction in body weight compared to aerobic ET alone. The available evidence from large randomized RCTs suggests similar weight losses after participating in a program composed of aerobic ET or combined aerobic and resistance ET ^30,31. However, combined programs may have enhanced effects for other health indicators such as glucose control. Observations from both the HART-D ³⁰ and DARE trials ³¹ suggest that an ET program composed of both resistance and aerobic ET promotes greater changes in hemoglobin A_1C compared to aerobic ET alone in adults with T2DM.

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. Wing et al. ⁵⁰ reported that, although ET and caloric restriction together may promote greater weight loss compared to caloric restriction alone, the differences in weight loss are not statistically significant. Miller et al. ⁵¹ performed a meta-analysis of weight loss interventions and determined that rate of weight loss was similar after ET and caloric restriction (1.0 kg/week) and caloric restriction alone (0.98 kg/week). The rate of weight loss observed in both these interventions far exceeded that which can be achieved by ET only (0.2 kg/week). Thus, the present literature supports that the majority of the weight loss from combined ET and caloric restriction can be attributed to caloric restriction. However, as will be discussed in this review, PA has an important role in weight maintenance, as well as increasing CRF ⁵², which improves in direct response to aerobic ET ¹⁰, but not with caloric restriction alone.

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 reduction), and had significant reductions in total fat mass, visceral fat and increased glucose disposal. However, the ET-induced weight loss group had a greater reduction in total fat mass compared to the diet induced weight loss group. Importantly, the exercise-induced weight loss improved CRF whereas the dietary group did not. In the group who performed ET without weight loss, the participants still experienced reductions in visceral fat and increased CRFs.

The observations by Ross et al. reaffirm that an ET program still confers health benefits to obese patients even in the absence of weight loss. Although dieting without ET has potential CV benefits, ET should be encouraged by clinicians to help their patients improve CRF levels, which is an independent risk factor for CV diseases, T2DM and mortality ¹⁰, and may further augment the negative energy balance created by caloric restriction. Lastly, Ross’ observations suggest that there is a rationale for ET to be a part of weight loss programs as the authors observed greater changes in visceral fat, oral glucose tolerance, and glucose disposal in the ET group with clinically significant weight loss compared to the group with ET without weight loss group.

Exercise and Weight Maintenance

The ACSM position stand on PA intervention strategies to promote weight loss and weight regain ¹⁵ emphasize the distinction between the minimum levels of PA to maintain health (150 minutes per week) and higher levels of PA to prevent weight regain (200 minutes per week). 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 observational and the retrospective nature of the existing literature from randomized trials. However, several studies in this area deserve mentioning. Using data from a PA weight loss study, Jakicic et al. ⁵³ observed a dose response between the amount of self-reported PA per week and long-term success with weight loss at 18 months of intervention (composed of caloric restriction and ET). Adults who exercised greater than 200 minutes per week (−13.1 kg) lost more weight compared to those who exercised between 150-199 min per week (−8.5 kg), and those that exercised less than 150 minutes week (−3.5 kg). A different study by Jakicic et al. ⁵⁴ observed similar findings in post hoc analyses of a weight loss intervention composed of both caloric restriction and exercise training in women. After 12 months of intervention, women with greater than 200 min/week (13.6%) had maintained significantly greater percentage of weight loss compared to those who had exercised at 150-199 min/week (9.5%), and less than 150 min/week (4.7%). Lastly, Andersen et al. ⁵⁵ evaluated the effect of low-fat diet (1200 kcals/day) in combination with either structured aerobic ET or lifestyle activity (patients were advised to increase their PA to recommended levels), and both groups lost approximately 8 kg of weight following 16 weeks of intervention. Weight maintenance was monitored for 1 year after the intervention, and those who were the most active lost additional weight (1.9 kg) whereas the group that was the least active regained a substantial amount of weight (4.9 kg). These data suggest that PA has an important role in the amount of weight regain following successful weight loss. Clinicians should therefore advocate that their patients attempting to reduce recidivism after weight loss engage in PA levels above 200 minutes/week ¹⁵.

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 restriction without exercise does not improve CRF levels ^39,52. As mentioned previously, ET has been shown to provide numerous health benefits even in the absence of weight loss. Therefore, if a patient is utilizing caloric restriction to lose weight, clinicians should always encourage an active lifestyle.

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 nature, therefore reverse causation may be an important factor to consider. More research is needed to determine the extent to which the relationships explained by the obesity paradox in individuals investigating weight loss programs or actively losing weight to verify whether maintaining higher weight levels are protective against mortality in these populations. Further, many studies which show weight loss with PA as a component have shown improvements in CV disease risk factors ⁹, progression to T2DM ⁵⁶, and mortality ¹⁰. Importantly, higher CRF levels appear to be protective against mortality in all BMI categories ¹⁴, and alter the relationship of the obesity paradox. Thus, the current literature suggests that overweight/obese adults with CVD should still participate in ET and a moderate weight loss program. However, further investigation of the obesity paradox is certainly warranted.

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 from a PA program unless the overall volume of ET is well above the minimum recommended levels. Patients wishing to lose weight should participate in physical activity and caloric restriction to improve the chances of weight loss. However, PA has a major role in the amount of weight regained after the initial weight loss. Overall clinicians should attempt to encourage participants to adhere to ET programs over the long-term regardless of the amount of weight loss achieved, as CV benefits are readily achieved in the absence of weight loss.

Acknowledgement

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