Physical Activity and Weight Management

Building the Case for Exercise

Ross E. Andersen, PhD; John M. Jakicic, PhD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 31 - NO. 9 - NOVEMBER 2003

In Brief: Exercise interventions are powerful tools for helping many patient populations. For those who need to manage their weight, an exercise program combined with diet modification may be key to losing weight and keeping it off. Many patients who are already at healthy weights find that physical activity helps to prevent weight gain. The good news is that accumulating frequent short bouts of moderately intense activity can be as effective as performing longer exercise sessions less often. Aerobic exercise alone may not be enough to preserve lean muscle mass when weight is lost, but incorporating resistance exercise may prevent reductions in resting metabolic rate and lean body mass.

The current obesity epidemic shows no sign of slowing down. Data from the 1999-2000 National Health and Nutrition Examination Survey (NHANES)1 show that almost 2 in 3 US adults are overweight (ie, have a body mass index [BMI] > 25 kg/m2) and 31% of US adults are obese (BMI > 30 kg/m2). These numbers represent significant increases in the prevalence of overweight and obesity from the NHANES III,2 conducted between 1988 and 1994. (For quick BMI calculations, see "Easy Body Mass Indexes," below.)

Easy Body Mass Indexes

Body mass index calculators are available at several sites on the Internet, such as:

 http://www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi.htm  http://www.keepkidshealthy.com/welcome/bmicalculator.html

A printable chart is available from the National Heart, Lung, and Blood Institute at http://www.nhlbi.nih.gov/guidelines/obesity/bmi_tbl.htm.

The lay public and many health professionals are wondering what is driving the obesity epidemic. Clearly, the overconsumption of high-energy, inexpensive, ubiquitous foods can partially explain the increased prevalence of obesity in the United States and around the world.3 Snack, drink, and food portion sizes have steadily increased over the past 25 years, but increased energy intake is not the sole cause of the obesity epidemic.

Examination of population trends indicates a possible link between physical inactivity and increases in body weight. The prevalence of obesity increased in every age-group from NHANES III (1988-1994) to NHANES 1999-2000. A steady increase in the prevalence of obesity is evident as US men move from the third decade of life (ages 20 to 29) to the seventh decade (ages 60 to 69) (figure 1).4 We have also noted a steady increase in the proportion of US men who report participating in no leisure-time activity at these ages (figure 2).5 A similar pattern of weight gain and inactivity exists for US women. Thus, as obesity increases from ages 20 to 70, a corresponding increase in physical inactivity may be partially related.

Moreover, nonobese persons tend to be more physically active in free-living environments than their obese counterparts. Investigators have reported that obese shoppers and commuters are more likely than nonobese pedestrians to ride an escalator than walk up the adjacent stairs.6

The Importance of Exercise

Physical activity is a key component of the energy balance equation in adults, and activity has a significant influence on body weight regulation. Numerous clinical studies7-14 have shown that the combination of dietary modification and exercise is the most effective behavioral intervention for weight loss in both short-term and long-term programs. Hagan et al7 compared diet, exercise, and diet plus exercise in men and women for 12 weeks. Their results support the incorporation of both diet and exercise in treatment programs and suggest that little change in body weight can be expected from exercise alone during a short-term intervention. These findings have been confirmed by other investigators who have shown that diet or the combination of diet plus exercise produces greater weight loss than exercise alone.8

Long-term interventions (> 1 year) are more effective when dietary modification is combined with exercise, and the impact on weight loss of exercise alone is less than diet alone or the combination of diet plus exercise.9-14 In a 1-year study9 of 131 men, body weight was reduced by 4.0 kg ± 3.9 kg (8.8 lb ± 8.6 lb) in men assigned to the exercise- only intervention, whereas men assigned to the diet-only group lost substantially more--7.2 kg ± 3.7 kg (15.9 lb ± 8.2 lb). Likewise, Wing et al10 reported minimal changes in body weight in an exercise-only group in a 2-year intervention in overweight adults.

Wood et al14 reported significantly greater weight loss following a 1-year intervention in men participating in a diet-plus-exercise intervention compared with those receiving only a diet intervention (8.7 kg ± 5.7 kg [19.2 lb ± 12.6 lb] versus 5.1 kg ± 5.8 kg [11.2 lb ± 12.8 lb]). After the same intervention in women, no significant difference was seen in weight loss in the diet-only (4.1 kg ± 5.5 kg [9 lb ± 12.1 lb]) versus the diet-plus-exercise (5.1 kg ± 5.3 kg [11.2 lb ± 11.7 lb]) groups.

However, others have shown that there is an additive effect in women.12,15 Dahlkoetter et al,12 who studied only women, reported significantly greater weight loss in the diet-plus- exercise group when compared with either diet alone or exercise alone for treatment. In addition, in a 20-week study of 21 women and 9 men, Wing et al15 reported significantly greater weight loss in a diet-plus-exercise intervention compared with a diet intervention alone. After an additional year of less intensive intervention, the diet-plus-exercise group maintained an average weight loss of 7.9 kg (17.4 lb) versus 3.8 kg (8.4 lb) in the diet-only group.

Getting Off the Couch

We live in a fast-paced world. Sedentary individuals often cite a lack of time to exercise as one of the most common barriers to becoming more active. Other patients tell us that they do not enjoy participating in vigorous activity or that they are embarrassed to go to a health club. In response to these concerns, we have developed new strategies to help overweight individuals who hope to manage their weight by increasing their levels of activity.

The classic exercise prescription was based on 30 minutes or more of sustained, vigorous activity performed three or four times per week. However, newer public health guidelines16 suggest that sedentary individuals can derive significant health benefits from accumulating 30 minutes or more of moderately intense activity, called lifestyle activity,17,18 on most days of the week. Lifestyle activity may include walking, using stairs when available, gardening, and looking for opportunities to expend energy.

Overweight women who followed a program of diet plus lifestyle activity lost amounts of weight similar to those who lost weight with diet plus programmed aerobic exercise.17 Both groups also demonstrated similar and significant improvements in body composition, lipid levels, blood pressure, and fitness. Considerable interest exists in the scientific literature about which activities are actually being done by patients who choose lifestyle activity. Walking was by far the most commonly cited activity in a study of patients who were randomized to lifestyle activity.19

A series of weight loss interventions by Jakicic and colleagues20,21 compared the effects of performing several 10-minute bouts of exercise throughout the day with a single, longer bout. Overweight patients who dieted in conjunction with short bouts of exercise were more likely to adhere to their exercise prescription than those who exercised in longer bouts. Sedentary people may find it easier to work shorter bouts of exercise into their busy schedules.

Wing and Hill22 described a group of adults who maintained weight loss and developed The National Weight Control Registry to track people who successfully maintain long-term weight loss (average 30 kg [66 lb] for 5.5 years). Most of the registered people report that they carefully watch their diets and try to avoid fried foods and snack foods. Only 9% of those registered reported maintaining their weight without regular physical activity. Of those who reported regular activity, most did a combination of lifestyle and regular programmed exercise. A much higher proportion of registered subjects report performing regular resistance training compared with the general population. It is not clear if weight training contributes to the long-term weight-maintenance success in the registered population,22 but Melby et al23 reported that acute strenuous resistance exercise is associated with modest, but prolonged, elevations in postexercise metabolic rate and possibly fat oxidation.

Saelens and Epstein24 tested a new paradigm to help patients manage their weight. For overweight children, they made sedentary activities (eg, watching movies, playing video games) contingent on riding a stationary bike. The control group had free choice of activities. The children in the contingent group increased their physical activity and reduced their television-related activity compared with the control group, even though other sedentary activities remained freely available. Sedentary behaviors, such as television watching, video games, and surfing the Internet, have been associated with a higher prevalence of obesity,25 partially because these behaviors expend relatively little energy. In one study,26 the prevalence of obesity was highest in children who watched 4 or more hours of television per day. These children also tended to consume more calories per day than those who watched less television. Thus, it is important for healthcare professionals to encourage overweight patients of all ages to reduce their sedentary behaviors.

Keeping the Weight Off

When examining behavioral interventions for overweight and obese patients, it is clear that maintenance of long-term weight loss has been less than optimal. On average, approximately 33% to 50% of weight lost is regained within 12 months following the initial weight loss period.8 Therefore, it is critical that interventions focus on strategies for maintaining long-term weight loss, and physical activity should be a key factor in those interventions.

Pavlou et al27 studied male law enforcement officers to examine the effectiveness of exercise in the treatment of obesity. Results of the 3-year study showed that individuals who exercised as part of their intervention showed better long-term weight loss compared with those who only dieted. Moreover, if exercise was added during the follow-up period, weight was either lost or maintained, but diet alone resulted in steady weight gain. Women who successfully maintained their weight loss for 7 months reported frequent participation in exercise in a study by Gormally et al.28 These findings suggest that exercise may be especially important for long-term effectiveness of behavioral weight loss programs.

The importance of exercise for enhancing long-term weight loss is further supported by findings from cross-sectional studies. In a study of individuals who lost at least 20% of their initial body weight and maintained the loss for at least 2 years, Colvin and Olson29 reported that 85% of the men and 78% of the women used increasing exercise as a strategy to maintain their weight loss. In a study by Kayman et al,30 90% of women who maintained a 20% weight loss for at least 2 years and 82% of nonobese control subjects reported performing regular exercise. Only 34% of the women who had not successfully maintained a weight loss reported exercising regularly.

Despite the demonstrated effectiveness of including exercise in weight loss interventions, the amount of exercise required to affect weight may be greater than typical public health recommendations designed to improve general fitness.31 The recommended 30 minutes of moderate-intensity activity burns up to 200 calories. (See "Easy Calorie Calculators, below") Initial results from the National Weight Control Registry show that individuals who maintained a weight loss of 30 kg ±15.5 kg (66 lb ± 34.1 lb) for an average of 5.6 years ± 6.8 years reported participating in a great deal of exercise (ie, 2,826 kcal ± 2,791 kcal of activity per week).32 This is roughly 400 kcal/day, an hour of activity every day, or the equivalent of a 70-kg (154-lb) person running about 25 miles per week (table 1). Moreover, Schoeller et al33 reported that individuals successful at maintaining their weight loss for 1 year participated in the equivalent of approximately 80 min/day of moderate intensity activity or 35 min/day of vigorous activity. Likewise, Jakicic et al21 reported that overweight women who maintained their weight loss for 1 year participated in approximately 40 min/day of moderate-intensity activity. Based on these findings, additional research is necessary to examine the dose-response relationship of exercise for optimal management of body weight.

Easy Calorie Calculators

The precise number of calories burned by doing an activity depends on the weight of the individual, the kind of activity, the intensity of the performance, and the duration of the exercise. Some Internet sites have fill-in formulas that will calculate energy expenditures for any body weight and for as little as 1 minute for many activities:

 http://www.primusweb.com/fitnesspartner/jumpsite/calculat.htm

 http://www.wvda.org/calcs/sport.html

TABLE 1. Number of Calories Burned in 1 Hour by a 70-kg (154-lb) Person for Various Activities

Estimated Activity Calories Burned* Running 5.2 mph (11.5 min mile) 633 Running 5 mph (12 min mile) 563 Running in place 563 Bicycling, moderate effort (12-14 mph) 563 Circuit training 563 Tennis, singles 563 Touch football, moderate effort 563 Walking up stairs 563 Cross-country skiing, light effort 493 Bicycling, light effort (10-12 mph) 422 Fishing, in stream, in waders 422 General aerobics 422 Stair climber or treadmill 422 Swimming, leisurely pace 422 Weight lifting or body building 422 Bicycling (stationary), light effort 387 Low-impact aerobics 352 Walking 4 mph 281 Walking 3 mph 246 Walking 2 mph 176 *Based on research data from the American College of Sports Medicine. Avoiding Weight Gain

In addition to the benefits of exercise for weight loss, increases in exercise and fitness may play an important role in preventing weight gain. DiPietro et al34 reported an inverse relationship between changes in fitness and changes in body weight. Based on odds ratios, each 1-minute improvement in maximal treadmill time decreased the risk of gaining 5 kg (11 lb) or more by 9% in women and 14% in men. The 1-minute improvement also reduced the odds of gaining 10 kg (22 lb) or more by 21% in both men and women.

Data from the NHANES-I Epidemiological Follow-up Study35 indicated that levels of recreational physical activity were inversely related to weight gain in both men and women. In addition, French et al36 found that either walking or higher-intensity activity predicted decreases in body weight for both men and women, but group sports and occupational activity may not be an effective strategy. Despite these findings, prospective data from randomized clinical trials that support the use of exercise for preventing weight gain are lacking and should be the focus of future research studies.

Effects on Lean Body Mass

When examining the role of exercise in weight loss, most clinical intervention studies have incorporated aerobic exercise, such as walking or stationary cycling. When weight is lost, loss of lean body mass and reductions in resting metabolic rate have been documented, and it does not appear that aerobic exercise can prevent these physiologic changes. Ross et al37 reported that an energy deficit, induced either by a reduction in energy intake or by an increase in energy expenditure through physical activity, resulted in similar decreases in body weight, body fatness, lean body mass, and resting energy expenditure. Thus, the addition of aerobic exercise may not be sufficient to combat the physiologic adaptations in lean body mass and resting energy expenditure that coincide with weight loss.

However, the incorporation of resistance exercise into weight loss interventions may minimize the reduction in lean body mass, which, in turn, may prevent the reduction in resting metabolic rate. The results of research trials in this area, though, have been mixed, and most research trials do not support this hypothesis. For example, Wadden et al38 examined the effects of aerobic and resistance training in overweight women who consumed a portion-controlled diet of approximately 900 to 925 kcal/day. Resistance training did not preserve lean body mass compared with diet alone, diet plus aerobic exercise, or diet plus the combination of aerobic and resistance exercise. Similar findings were reported by Donnelly et al39,40 when the diet consisted of approximately 520 kcal/day consumed in the form of liquid meals.

In a 90-day study using about 800 kcal/day, Donnelly et al41 found that the same amount of weight and fat composition was lost by both the resistance-trained and control groups. However, biopsies of skeletal muscle showed significantly increased muscle fibers in the resistance group, suggesting that a decrease in lean body mass resulted from the loss of other lean tissue.

Similarly, Ross et al42 used magnetic resonance imaging to evaluate muscle mass in 14 strength-trained women whose diet produced a 1,000-kcal/day deficit. The study found that skeletal muscle was preserved and adipose tissue was substantially reduced. The interpretations of the results of this study are limited by the lack of a diet-only intervention group.

A 20-week study by Marks et al43 compared groups of overweight women who used diet, diet plus cycling, diet plus resistance training, diet plus resistance training and cycling, and a control group to determine which interventions would preserve fat-free mass. Hydrostatic weighing showed that all groups maintained fat-free mass, but only the diet plus resistance training and cycling group lost significant body fat.

Based on the findings reported to date, it appears that the role and effectiveness of resistance training in weight loss and body weight regulation of overweight individuals is not clear. Additional research is warranted.

Getting Patients Started

When a physician delivers a clear and concise message about the importance of regular physical activity, most sedentary people will listen. The best place to start is to ask your patients what type of activity (if any) they have done in the past. Overweight patients who have participated on sports teams may feel quite comfortable resuming a traditional exercise program. In contrast, overweight individuals who have never taken part in regular exercise may feel confident only by starting with increasing their lifestyle activities. As they progress, the physician can explore their willingness to consider increasing the relative intensity of their activity.

Exercise prescriptions that have been tailored to meet the individual's level of interest, readiness, and time availability are more likely to be followed.44 The task may seem less daunting to busy patients if they are encouraged to start with one 10-minute bout of walking every day. The goal becomes adding 10-minute bouts or walking longer each session as they become able. Activity totaling 30 min/day is enough to produce significant health benefits, whether or not patients lose weight. When combined with diet, weight loss should become an attainable goal when they consistently do the equivalent of four 10- minute bouts a day most days of the week. By starting gradually and building on successes, patients can reduce their sedentary time. Maintaining or increasing leisure-time activity will also help forestall the dreaded weight regain.

Addressing issues such as weight management and sedentary lifestyle at each office visit is important. Keeping detailed notes in the medical chart can help start the dialogue during follow-up visits and reinforce healthy habits. Overweight individuals can enjoy many of the health benefits of an active lifestyle, even if they do not lose weight. Motivating Behavioral Change

Although many people know that regular exercise can help them lose weight and keep it off, many are discouraged from adopting active lifestyles because they don't know how much exercise to perform to meet their goals. Perceived barriers to exercise keep many overweight sedentary people believing that losing weight takes too much effort, so they do not try. Many feel that losing weight is futile because they will just gain it all back. As the obesity epidemic spreads, clinicians need to promote activity and provide exercise prescriptions that encourage patients to attempt weight loss and to lead healthier, more active lives.

References

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Donnelly JE, Pronk NP, Jacobsen DJ, et al: Effects of a very-low-calorie diet and physical-training regimens on body composition and resting metabolic rate in obese females. Am J Clin Nutr 1991;54(1):56-61 40. Donnelly JE, Jacobsen DJ, Jakicic JM, et al: Very low calorie diet with concurrent versus delayed and sequential exercise. Int J Obes Relat Metab Disord 1994;18(7):469-475 41. Donnelly JE, Sharp T, Houmard J, et al: Muscle hypertrophy with large-scale weight loss and resistance training. Am J Clin Nutr 1993;58(4):561-565 42. Ross R, Pedwell H, Rissanen J: Response of total and regional lean tissue and skeletal muscle to a program of energy restriction and resistance exercise. Int J Obes Relat Metab Disord 1995;19(11):781-787 43. Marks BL, Ward A, Morris DH, et al: Fat-free mass is maintained in women following a moderate diet and exercise program. Med Sci Sports Exerc 1995;27(9):1243-1251 44. Christmas C, Andersen RA: Exercise and older patients: guidelines for the clinician. 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Dr Andersen is an associate professor of medicine in the division of geriatric medicine and gerontology at the Johns Hopkins University School of Medicine in Baltimore. Dr Jakicic is an associate professor in the physical activity and weight management research center at the University of Pittsburgh. Address correspondence to Ross E. Andersen, PhD, Johns Hopkins University School of Medicine, Division of Geriatric Medicine and Gerontology, 5505 Hopkins Bayview Cir, Baltimore, MD 21224; address e-mail to [email protected].

Disclosure information: Drs Andersen and Jakicic disclose no significant relationship with any manufacturer of any commercial product mentioned in this article. No drug is mentioned in this article for an unlabeled use.