A 52-year-old overweight man with hypertension and diabetes has made some dietary changes, but he has not initiated an exercise program for weight loss. He wonders if exercise will really make a difference.
How effective is exercise in reducing body weight and improving cardiac risk factors in overweight or obese patients?
Exercise leads to a weight loss of 1 lb, 2 oz to 16 lb, 12 oz (0.5 to 7.6 kg), compared with a 3-oz (0.1-kg) weight loss to a weight gain of 1 lb, 9 oz (0.7 kg) with no treatment. Patients participating in higher-intensity exercise lose 3 lb, 5 oz (1.5 kg) more than those participating in low-intensity exercise. Regardless of whether the patient loses weight, exercise improves diastolic blood pressure and triglyceride, high-density lipoprotein, and glucose levels. When a low-calorie diet is compared with exercise alone, a low-calorie diet leads to more weight loss (6 lb, 3 oz to 29 lb, 16 oz [2.8 to 13.6 kg] versus 1 lb, 2 oz to 16 lb, 12 oz). However, trials with three to 12 months of follow-up show that participants who combine a low-calorie diet with exercise lose 2 lb, 7 oz (1.1 kg) more than those who only diet.1
In the United States and in some European countries, an estimated 50 percent of adults are overweight.2 The health consequences of overweight and obesity include decreased life expectancy and increased risk of heart disease, stroke, hypertension, dyslipidemia, type 2 diabetes, gallbladder disease, osteoarthritis, and sleep apnea.
The benefits of exercise extend beyond weight loss. Improvement in cardiovascular risk factors (e.g., decreased blood pressure; cholesterol, triglyceride, and fasting serum glucose levels) occurs in patients who adopt a regular exercise program. Even if exercise produces minimal weight loss, obese patients with a good cardiorespiratory fitness level have been shown to have a reduced cardiovascular mortality risk compared with lean but unfit patients.3
Regular exercise also appears to play an important role in maintaining long-term weight loss and in preventing weight regain. Patients in the National Weight Control Registry who continued to exercise were more likely to maintain their weight loss compared with those who did not continue to exercise.4 However, less than 25 percent of patients who attempt weight loss on their own incorporate exercise into their weight loss plans.5 Lack of ongoing physical activity may be responsible for the prevalence of weight regain after initial weight loss.
Although high-intensity exercise leads to a slightly greater weight loss than low-intensity exercise, initiating a high-intensity regimen is not practical for many obese patients. Degenerative joint disease is common in these patients, and appropriate exercise modification is necessary. Low-intensity exercise (e.g., walking) may be strenuous even for obese patients without joint problems. Although lean, fit persons may consume only 35 percent of the maximum volume of oxygen (VO2) while walking, obese persons have much higher VO2 requirements. Therefore, a long, brisk walk is not necessarily low-intensity exercise in obese persons.2
Background: Clinical trials have shown that exercise in adults with overweight or obesity can reduce body weight. There has been no quantitative systematic review of this topic in the Cochrane Library.
Objectives: To assess exercise as a means of achieving weight loss in persons with overweight or obesity, using randomized controlled trials (RCTs).
Search Strategy: Studies were obtained from computerized searches of multiple electronic bibliographic databases. The last search was conducted in January 2006.
Selection Criteria: Studies were included if they were RCTs that examined body weight change using one or more physical activity intervention in adults with overweight or obesity at baseline and if they had a loss to follow-up of participants of less than 15 percent.
Data Collection and Analysis: Two authors independently assessed trial quality and extracted data.
Primary Results: The 43 studies included 3,476 participants. Although significant heterogeneity in some of the main effects' analyses limited ability to pool effect sizes across some studies, a number of pooled effect sizes were calculated. When compared with no treatment, exercise resulted in small weight losses across studies. Exercise combined with diet resulted in a greater weight reduction than diet alone (weighted mean difference [WMD], −2 lb, 7 oz [−1.1 kg]; 95% confidence interval [CI], −3 lb, 5 oz to −1 lb, 5 oz [−1.5 to −0.6 kg]). Increasing exercise intensity increased the magnitude of weight loss (WMD, −3 lb, 5 oz; 95% CI, −5 lb, 1 oz to −1 lb, 9 oz [−2.3 to −0.7 kg]). There were significant differences in other outcome measures such as serum lipids, blood pressure, and fasting plasma glucose. Exercise as a sole weight loss intervention resulted in significant reductions in diastolic blood pressure (WMD, −2 mm Hg; 95% CI, −4 to −1), triglycerides (WMD, −17.7 mg per dL [−0.20 mmol per L]; 95% CI, −0.3 to −0.1), and fasting glucose (WMD,−3.6 mg per dL [−0.20 mmol per L]; 95% CI, −0.3 to −0.1). Higher-intensity exercise resulted in greater reduction in fasting glucose than lower-intensity exercise (WMD, −5.4 mg per dL [−0.30 mmol per L]; 95% CI, −0.5 to −0.2). No data were identified on adverse events, quality of life, morbidity, costs, or mortality.
Reviewers' Conclusions: The results of this review support the use of exercise as a weight loss intervention, particularly when combined with dietary change. Exercise is associated with improved cardiovascular disease risk factors even if no weight is lost.
These summaries have been derived from Cochrane reviews published in the Cochrane Database of Systematic Reviews in the Cochrane Library. Their content has, as far as possible, been checked with the authors of the original reviews, but the summaries should not be regarded as an official product of the Cochrane Collaboration; minor editing changes have been made to the text (http://www.cochrane.org)
Most trials in this review included 15 to 60 minutes of exercise (median exercise duration of 45 minutes per session) three to five days per week. The Centers for Disease Control and Prevention and the American College of Sports Medicine (ACSM) recommend a minimum of 30 minutes of moderate-intensity exercise on most days (interpreted as approximately 150 minutes per week).6 However, because glycogen is preferentially burned during the first 20 minutes of exercise, at least 30 minutes of exercise is necessary to begin burning fat stores.2 Consequently, the ACSM and the International Association for the Study of Obesity recommend that overweight persons exercise more than 30 minutes per day to control body weight.7
A variety of exercises were included in this review: walking, jogging, cycle ergometry, weight training, aerobics, ball games, and calisthenics. Patients without joint disease who can tolerate walking should be encouraged to walk for exercise. Age, degenerative disease, gait disturbances, uneven or slippery surfaces, heavy clothing, and skin friction may impede a walking regimen. Cycling and swimming may be acceptable alternatives. A recent study showed that walking on land or in water leads to similar reductions in body weight and body fat8; this refutes an earlier study that suggested swimming is not effective at reducing body fat.9
There are many barriers to sustaining an exercise program. Some persons find that 30-minute sessions are too long; however, intermittent exercise (e.g., three 10-minute sessions per day) improves cardiovascular fitness. Although some persons think they must join a health club to achieve an appropriate exercise level, a home-based, self-directed approach can be just as effective as exercising at a health club.7 Self-monitoring (e.g., pedometers) and goal setting (e.g., gradual increase in number of steps) may help patients comply with exercise regimens.
When counseling overweight patients about adopting a diet and exercise program, physicians should honestly and openly discuss the patient's weight problem and weight loss goals. In a 1994 survey of 61,000 obese adults, only 42 percent reported that their health care provider advised them to lose weight; this number decreased to 40 percent in a 2000 survey.10
Some overweight patients will respond to a physician's advice to adopt an exercise program, whereas others may require additional motivation and education. Those who adopt a program may need frequent reminders and social support.11 To meet the weight loss needs of overweight and obese patients, family physicians should fill the roles of educator, coach, and facilitator.