Exercise, an Active Lifestyle, and Obesity
Making the Exercise Prescription Work
Ross E. Andersen, PhD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 27 - NO. 10 - OCTOBER 1, 1999
In Brief: An active lifestyle can play an important role in helping overweight patients both lose and manage their weight. The traditional exercise prescription of regular bouts of continuous vigorous exercise may need to be modified to increase rates of adoption and compliance. Recent data suggest that accumulating several short bouts of moderate to vigorous activity each day may improve adherence to the program. Understanding the barriers to activity that overweight people face—such as fear or embarrassment—can help physicians prescribe appropriate exercise routines, which may ultimately help them with better weight management.
Obesity is a serious and increasingly prevalent health problem. In the United States, an estimated 33.3% of men and 36.4% of women have a body mass index (BMI) of 27 kg/m2 or greater (a BMI under 26 kg/m2 is considered healthy) (1). Moreover, 14.4% of American men and 16.2% of women are now considered obese using a standard of 30 kg/m2 BMI or greater. In addition, 26% of American children are overweight and 10% are severely overweight (2). These statistics represent a dramatic increase over a relatively short period.
This increased prevalence of overweight is paralleled by an increase in inactivity. Most jobs today are sedentary (3), and 24% of Americans report participating in no leisure-time activity (4). Overweight people are even more likely to report being inactive.
Automobiles, public transportation, and other labor-saving devices also contribute to sluggish lifestyles (5). Prentice and Jebb (6) recently reported that the prevalence of obesity has doubled in England over the past 10 years. This trend was mirrored by an increase in the number of cars and televisions per household.
My colleagues and I (7,8) recently investigated the relationships among physical activity, television watching, body weight, and level of fatness in American children. We found a very strong relationship between television watching and fatness. Furthermore, 26% of American children watched 4 or more hours of television each day—a rate that was higher among Mexican-American (30%) and African-American (43%) children. Boys and girls who were high television watchers and not regularly active were fatter than children who were low television watchers and highly active.
Americans spend billions of dollars annually on diet books, exercise equipment, and weight-loss programs. Unfortunately, losing weight is difficult for most patients, and most of those who do lose weight ultimately regain it. These well-publicized statistics may leave physicians wondering how to counsel their overweight patients—or if it is even worth trying.
Exercise and Weight: Current Evidence
Simply having patients increase their level of exercise without restricting calorie intake is a relatively ineffective way to lose weight. When combined with a healthy diet, however, increased aerobic and strength exercise may result in optimal changes in body composition by contributing to a negative energy balance and preserving lean body mass.
Metabolic cost of activity. It is well accepted that remaining sedentary is associated with an increased risk of obesity. This is supported by the fact that the prevalence of obesity has more than doubled in the United States since 1900, despite a 10% decline in food intake (9). Hence, the goal of most weight-management programs should be to decrease energy intake while simultaneously increasing energy expenditure and reducing sedentary time.
Some studies have reported that adding aerobic exercise to the weight-loss program can increase the rate of weight loss. One of the key benefits of exercise is the increased calories that are burned beyond resting levels. For example, it is not uncommon for a beginning exerciser to expend energy at a rate 5 to 7 times above resting levels (10).
Furthermore, the resting metabolism does not plunge back to resting levels immediately after an exercise bout. Active individuals may have slightly higher metabolic rates than their sedentary counterparts (11). This may be due to the metabolic demands of resynthesizing glycogen stores and repairing tissue damage (12). Melby et al (13) reported that resistance exercise may lead to greater postexercise oxygen consumption than endurance exercise does.
Favorable body composition changes. The primary objective of most overweight people is to lose fat. Ballor and Poehlman (14) conducted a meta-analysis to examine the effects of exercise training on fat-free mass (FFM) preservation during diet-induced weight loss. They found that 24% to 28% of weight loss will come from FFM in the nonexercising dieter, while only 11% to 13% of weight loss will come from FFM in those who engage in vigorous aerobic and resistance exercise while dieting. Thus, exercise appears to attenuate, but not totally prevent, the loss of lean tissue. This is an important point since the loss of lean tissue is known to be highly related to reductions in resting metabolic rate.
A review of 55 studies found that adults who try to lose weight with a program of exercise alone will, on average, reduce their fat percentage by 1.6% (15). A few of these studies involving very lengthy and strenuous exercise protocols have reported weight losses of up to 25 lb (11 kg). However, the volume of activity used in these trials would not be feasible for most overweight individuals.
Weight management. Longitudinal and cross-sectional studies have consistently reported that physical activity is inversely related to weight (16). Although exercise does not consistently predict weight loss in the short term, it is commonly cited as the strongest predictor of long-term success in weight management.
Most physicians recognize that an active lifestyle plays an important role in long-term weight management. Kayman et al (17) reported that 90% of women who have lost weight and kept it off report exercising on a regular basis. In contrast, only 34% of women who regain their lost weight report regular activity.
My colleagues and I (8) recently examined weight-regain patterns in 40 women who had lost weight in a 16-week treatment program. Over the year that followed treatment, we found that the most active third of patients actually lost weight. The middle third reported meeting the current surgeon general's recommendations (4) in only 52% of the weeks in the year following treatment, but they maintained their full end-of-treatment weight loss. The least active third, in contrast, steadily gained weight throughout the year after treatment. This shows that, when attempting to manage their weight, patients should strive to incorporate physical activity into their daily lives—but they should realize that even irregular activity is much better than nothing at all.
General health benefits. Exercise will benefit patients even if they don't lose weight. Lee et al (18) examined the health benefits of leanness and the hazards of obesity while simultaneously considering cardiorespiratory fitness. They followed 21,925 men, aged 30 to 83. All participants had a baseline body-composition assessment and a peak treadmill exercise test. During 8 years of follow-up, 428 of these died (144 from cardiovascular disease, 143 from cancer, and 141 from other causes).
After the researchers adjusted for confounding variables, they found that unfit lean men had double the risk of all-cause mortality when compared with fit lean men (relative risk, 2.07; 95% confidence interval, 1.16 to 3.69; P = 0.01). Unfit lean men also had a higher risk of all-cause and cardiovascular disease mortality than did men who were fit and obese. Similarly, unfit men with small waistlines (< 87 cm) had a greater risk of all-cause mortality than did fit men with greater girths (> 99 cm). The investigators concluded that the health benefits of leanness may be limited to fit men, and that exercise is very beneficial to overall health even if no weight is lost.
Psychological effects. Brownell (9) has also speculated that the psychological impact of exercise is a key mechanism for weight control. Patients who exercise regularly are likely to be less depressed, have higher self-esteem, and have an improved body image (9). Regular exercise may also reduce stress and anxiety—elements that represent a high-risk situation for many dieters (17). An active lifestyle seems to be one of many factors that converge to help people manage their weight.
Barriers to Activity
Most patients recognize that regular exercise is important from both health and weight management perspectives. Given this information, why do so few participate? We recently surveyed 52 overweight, sedentary patients who were beginning a weight-loss program (unpublished data). Their four greatest barriers to regular activity were:
A lack of time has consistently been reported as the greatest obstacle to being active (4,10,19). Given this information, new strategies to promote physical activity are being explored that stray from the classic exercise prescription of at least 30 minutes of uninterrupted vigorous activity done 3 or more days per week.
Lifestyle Activity and Regular Exercise
The American College of Sports Medicine (ACSM), the Centers for Disease Control and Prevention, the National Institutes of Health, and the surgeon general have recommended that all Americans attempt to accumulate 30 minutes or more of moderate-intensity physical activity on most or, preferably, all days (4,20,21). The aim of these recommendations is to offer a greater range of choices for sedentary people, especially those who do not enjoy traditional activity.
DeBusk et al (22) have shown that three 10-minute bouts of aerobic exercise yield fitness improvements comparable to (though slightly less than) those from one continuous 30-minute session. Moreover, the strategy of splitting up the workouts may result in better exercise adherence and increased weight loss (23,24).
The concept of "lifestyle activity" encourages patients to look for opportunities every day to increase energy expenditure. Patients are encouraged to work short bouts of activity into their daily routines, which may fit more easily into busy schedules. Here are a few examples for increasing daily energy expenditure:
Focusing on lifestyle activity may be a suitable initial exercise program for an obese patient. This is especially true for those who do not have time for a traditional exercise program or those who simply do not enjoy exercise.
My colleagues and I (8) recently compared health outcomes in a group of obese women who were randomized to a program of either diet plus lifestyle activity or diet plus aerobic exercise. After 16 weeks of treatment, we found similar and significant improvements in fitness, serum lipid profiles, blood pressure, and weight loss. Interestingly, there was a trend for the patients in the lifestyle group to maintain their weight loss during the year following treatment better than did the aerobic group. We believe the lifestyle group created habits that were maintained during the follow-up year (figure 1: not shown).
In addition, Dunn et al (25) recently reported that in 235 previously sedentary adults, a lifestyle activity intervention is as effective as a structured exercise program in improving physical activity, aerobic fitness, and blood pressure.
From lifestyle to traditional workouts. Traditional exercise prescriptions have been devised to optimize fitness levels, but obese individuals too often find it difficult to comply with a vigorous exercise regimen. Physicians, therefore, need to counsel patients that lifestyle activity counts. My colleagues and I have found that the model of lifestyle activity is exciting to patients as they begin the treatment, since most perceive that they can successfully comply with the prescription.
We also suspect that lifestyle activity may be a gateway into a more traditional exercise program, though this has not been tested. We have noticed that patients who have increased their lifestyle activity for an extended period begin to gain confidence that they can successfully attempt a vigorous exercise program. It is also important for healthcare professionals to encourage patients to reduce the time they spend doing sedentary activities (see the Patient Adviser, "Simple Steps for Increasing Activity and Losing Weight," page 51).
The exercise prescription for the obese individual who is ready to start a traditional exercise program should involve not only cardiorespiratory fitness enhancement, but also strength training, lifestyle activity, and flexibility exercises. Clinicians should ensure that cardiovascular intensity is at the low end of the appropriate target heart rate range (close to 60% rather than 90% of maximal heart rate) (26). The ACSM recommends aerobic exercise 20 to 60 minutes (which can be broken into 10-minute bouts) 3 to 5 days per week, resistance training 2 to 3 days per week, and flexibility training 2 to 3 days per week (27).
Exercise history and other key questions. Assessing the exercise history of overweight patients can help in designing an exercise program. Physicians can ask if they participated in youth sports, activities in college, or exercise as an adult. Queries about exercise enjoyment and recent exercise history will also help physicians to prescribe a tailored program (3). Formerly active people may feel quite comfortable resuming a traditional exercise program, whereas patients who have never been regularly active may be overwhelmed with the notion of starting to exercise.
Obesity typically is associated with low levels of leisure-time physical activity (28). Beginning a moderate or vigorous exercise routine may be threatening to an obese patient who feels winded by simply taking one flight of stairs. The fear of vigorous exercise is often cited as a barrier to increasing activity levels. Physicians should ask about patients' comfort with starting an exercise program; this will provide an opportunity to educate and to allay fears.
Advice and Follow-Through
Given that a sedentary lifestyle and obesity have been added to the American Heart Association's list of major risk factors for heart disease (29), it is important for physicians to address these two modifiable risk factors. If physicians fail to address these health concerns, patients may perceive that these issues are not important.
Overweight people should be encouraged to pursue a sensible meal plan and to slowly increase their activity. Recommendations should be recorded in the medical charts, and body weight and exercise habits should be addressed at each office visit. By encouraging overweight individuals to engage in physical activity, physicians will help them live more healthfully.
Dr Andersen's work is supported by grant 97214G from the John A. Hartford Foundation.
Dr Andersen is an assistant professor of medicine in the Division of Geriatric Medicine and Gerontology at the Johns Hopkins University School of Medicine in Baltimore. He is a fellow of the American College of Sports Medicine. Address correspondence to Ross E. Andersen, PhD, FACSM, Johns Hopkins School of Medicine, 4940 Eastern Ave, Suite 025, Baltimore, MD 21224-2780; e-mail to [email protected].