Exercise and Weight Loss
By Dónal P. O'Mathúna, BS (Pharm), MA, PhD. Dr. O'Mathúna is Senior Lecturer in Ethics, Decision Making & Evidence, School of Nursing, Dublin City University, Ireland; he reports no financial relationship to this field of study.
The worldwide epidemic of overweight and obesity continues to deteriorate.1 The personal and societal health and economic consequences of obesity have been well documented.2 Mention obesity or the need to lose weight, and the next thing to be brought up in many discussions is exercise. Either intuitively, or because of the attention this topic receives, many believe they are not getting enough exercise. If only we could get to the gym more, or at least out for a walk, all those extra pounds would melt away.
The solution seems to be fairly straightforward: People lose weight when energy output exceeds energy intake. The trend toward obesity is matched by an increasingly sedentary lifestyle, particularly in developed countries. Since physical activity increases energy output, exercise would seem to be an important part of any solution. Hence, a whole exercise industry has arisen claiming that physical activity can burn calories, reduce body fat, control your weight, and reduce your appetite.3 The number of gym club memberships has doubled since 1993, now totaling $19 billion per year in the United States alone.4
Apparently flying in the face of common sense, Yahoo! News published on-line in August 2009 an article entitled "Why Exercise Won't Make You Thin."5 Later that month, the article was the cover story for Time magazine and is currently the most frequently read article on the Time magazine web site.4 Patients are likely to be wondering whether the advice they may have received to exercise more is justified. Should they join gyms and don shorts or sweat pants when they get home from work? Time has raised serious questions, and patients need evidence-based answers.
A systematic review was published in 2009 that examined randomized controlled trials (RCTs) of exercise, dietary, and/or behavioral interventions for weight loss in healthy adults.1 To be included, studies had to compare people engaged in physical training or exercise with those who exercised and received a dietary and/or behavioral intervention. Studies were also required to include a one-year follow-up evaluation or to last at least one year. Twelve RCTs met the inclusion criteria. Aerobic training was the exercise method in all studies, with walking being a part of all, but also with some participants using a step-up machine, jogging, or cycling. Combinations of individual and group training were included. Much variability occurred in the duration, frequency, and intensity of training. Similar variability occurred with the dietary recommendations. The purpose of behavioral therapy was consistently stated as changing behavior, thinking, and feelings about body weight, but the interventions themselves were poorly described.
At the end of the intervention period, most studies found that participants had lost significant amounts of weight. The largest weight loss (ranging from 8 to 12 kg, i.e., 17-27 lbs) occurred in those groups that combined aerobic training with dietary and behavioral interventions. The next largest loss of weight occurred in those groups that used exercise and dietary interventions. The least amount of weight was lost in those groups that used aerobic training alone.
Eight of the studies included follow-up periods of up to two years. The same general patterns existed in the degree of successful weight maintenance. The largest effect size was seen in those groups that combined exercise, dietary, and behavioral interventions. Although the groups that included exercise were more successful than control groups without exercise, groups using exercise as the sole intervention were the least successful. The reviewers concluded that exercise is important in combination with other weight-loss strategies, but that "training alone cannot be expected to lead to any significant weight loss, regardless of the type of training or exercise plan."1 Subsequent studies have been published supporting this conclusion.6,7
Looking for Solutions
Part of the problem with exercise and weight loss is that a complex relationship exists between exercise and food intake. In studies where calorie intake was held constant and exercise was added, weight loss occurred. In calorie-restriction programs, weight loss was maintained better when exercise was part of the maintenance program. In one study with a very low-calorie diet and behavior therapy, participants lost an average of 27.2 kg. Two to three years later, those who reported high levels of physical activity had maintained their weight loss better (17.5 kg down from baseline) than those who exercised moderately (9.3 kg) or not at all (5.6 kg).8
Another issue is that the number of calories consumed in physical activity is often overestimated by people. The accompanying Table lists the number of calories consumed per hour by various activities.9 After running for an hour, or hiking in a park for an hour, you decide to reward yourself at a local coffee shop. A muffin and a whole-milk cappuccino will replace 573 calories and negate the run; if you went on the hike, you will need to limit yourself to a skinny muffin and a non-fat latte, which will replace 387 calories.10
Thirty minutes of physical activity on most days of the week is often recommended. This brings many health benefits, but by itself is insufficient for most people to maintain a desirable body weight (BMI, 18.5-24.9 kg/m2). Sixty minutes of daily physical activity is necessary for most people to prevent undesirable weight gain, and 60-90 minutes per day is necessary for weight loss in addition to reducing caloric intake.2 Thus, many organizations now recommend an hour or more of daily exercise in weight-management programs.11
However, while a small number of studies have shown that short-duration exercise can lead to slightly decreased food intake, as the duration of exercise lengthens, food intake can increase through appetite stimulation.12 Many studies lasting more than 25 weeks have noted that actual weight loss is often less than that predicted based on the energy expended by the additional exercise.13 This phenomenon has been called "compensation" and in some cases people lose only 30% of the weight predicted.11 Anecdotally, this has been explained in terms of people exercising and then compensating in a number of ways that counteract the exercise. Compensation can occur as a high-calorie "reward" for exercising, feeling ravenous and consuming additional food, or being too tired for any further activity later in the day.4
The first controlled study to examine different durations of exercise for weight loss was published in 2009.11 More than 400 sedentary, overweight, or obese postmenopausal women were randomized to one of four groups. The four groups averaged either 194, 136, 72, or 0 minutes of supervised exercise per week (beyond normal activities). The women were asked not to change their dietary habits and to complete a monthly health questionnaire. After six months, all four groups lost weight, with the differences between the groups not being statistically significant. However, the group that exercised the most had much less weight loss compared to what was predicted. In the group that averaged 136 minutes per week, the predicted and actual losses matched closely. The group that exercised the least had slightly more weight loss than predicted. The authors concluded that as the amount of exercise increases, people use compensatory mechanisms that counteract weight loss. They encouraged further research to understand the causes and types of compensation, but raised concerns that current recommendations (to exercise more than 200 minutes per week) may be counterproductive. At the same time, they noted that about one-quarter of the women engaging in the additional exercise did lose weight as predicted, thereby highlighting the importance of individual variability in weight-loss programs.
The health benefits of exercise are many: It protects against the loss of lean body mass, improves cardiorespiratory fitness, reduces obesity-related health risks, and can improve a person's psychological and emotional sense of well-being.2
However, on its own, exercise is not an effective strategy for reducing weight, and may even contribute to weight gain. Additional exercise carries the risk of stimulating appetite and leading people to consume more calories. At the same time, exercise has an important role to play within a weight-management program that includes dietary and behavioral interventions. Regular physical activity is particularly important as part of a lifestyle that promotes maintenance of fitness and healthy body weight.
Losing weight is challenging and multifaceted. No one strategy will work for everyone. Exercise, reduced calorie intake, behavioral interventions, and social support are required by most people to be successful in losing weight. Modest, gradual weight loss is most effective, generally in the range of 0.5-1 lb per week.14 Since people usually become overweight or obese gradually over years, patients should be reminded that it will take time and perseverance to reach their target weight. Physical activity that is regular and incorporated into an active lifestyle will play an important role in maintaining a healthy body weight.
Walking is the most commonly recommended activity because it can be incorporated into most people's lifestyles relatively easily. The activity can also be carried out in smaller portions throughout the day. For some obese people, however, even walking can be a strenuous activity and cause discomfort or even pain.14 Individual considerations must be taken into account in recommending exercise prescriptions. A detailed list of activities at different intensities can be found on the CDC's web site.15 Even if exercise is not the panacea for weight loss, its health and psychological benefits make it vitally important.
1. Södlerlund A, et al. Physical activity, diet and behaviour modification in the treatment of overweight and obese adults: A systematic review. Perspect Public Health 2009;129:132-142.
2. Okay DM, et al. Exercise and obesity. Prim Care 2009;36:379-393.
3. Hayes C. What is physical activity and why should we do it? Perspect Public Health 2009;129:111-112.
4. Cloud J. Why exercise won't make you thin. Time 17 Aug 2009:26-31. Available at: www.time.com/time/health/article/0,8599,1914857,00.html. Accessed Sept. 7, 2009.
5. Cloud J. Why exercise won't make you thin. Yahoo! News 6 Aug 2009. Available at: http://news.yahoo.com/s/time/20090806/hl_time/08599191485700. Accessed Aug. 10, 2009.
6. Kerksick C, et al. Effects of a popular exercise and weight loss program on weight loss, body composition, energy expenditure and health in obese women. Nutr Metab (Lond) 2009;6:23.
7. Caudwell P, et al. Exercise alone is not enough: Weight loss also needs a healthy (Mediterranean) diet? Public Health Nutr 2009;12:1663-1666.
8. Hartman WM, et al. Long-term maintenance of weight loss following supplemented fasting. Int J Eat Disord 1993;14:87-93.
9. Office of Disease Prevention and Health Promotion, U.S. Department of Health and Human Services. Nutrition and Your Health: Dietary Guidelines for Americans, 2005. Available at: www.health.gov/DIETARYGUIDELINES/dga2005/report/HTML/table_e6.htm. Accessed Sept. 7, 2009.
10. Calculated at: www.calorieking.com on Sept. 8, 2009.
11. Church TS, et al. Changes in weight, waist circumference and compensatory responses with different doses of exercise among sedentary, overweight postmenopausal women. PLoS One 2009;4:e4515.
12. Doucet E, et al. Appetite after weight loss by energy restriction and a low-fat diet-exercise follow-up. Int J Obes Relat Metab Disord 2000;24:906-914.
13. Ross R, Janssen I. Physical activity, total and regional obesity: Dose-response considerations. Med Sci Sports Exerc 2001;33:S521-S527.
14. Poirier P, Despres JP. Exercise in weight management of obesity. Cardiol Clin 2001;19:459-470.
15. Centers for Disease Control and Prevention. General Physical Activities Defined by Level of Intensity. Available at: www.cdc.gov/nccdphp/dnpa/physical/pdf/PA_Intensity_table_2_1.pdf. Accessed Sept. 8, 2009.