In the first four posts in this series I looked at the history behind exercise and weight loss, how physical acitivity affects bodyweight, compensatory mechanisms and why some people gain weight from exercise. While these posts are important to understand how physical activity affects body composition and invidual differences in exercise-induced weight loss, the real issue still remains; does exercise make you lose weight?
There are hundreds of studies investigating the relationship between physical activity and fat loss, and a meta-analysis by Miller et al. (1997) looked at all the research done between 1969 and 1994 that met the criteria of the review (1). Most of the studies in that time period were done on the moderately obese and middle aged population. The meta-analysis shows that a 15-week diet or diet plus exercise program, produces a weight loss of about 11 kg, and that diet or a combined approach of both diet and exercise is far more effective than exercise on it’s own. A newer meta-analysis by Wu et al. (2009) also supports these findings (2).
Individuals respond differently
While some people can be labelled as “responders”, others experience little weight loss with physical activity alone. One of the studies reviewed by King et al. (2012) shows that 12 weeks of supervised exercise designed to burn a total of 2500 calories per week led to an average weight loss of 3.2 kg. While all of the test subjects performed identical exercise routines some lost more than 10 kg’s, while others actually gained weight (3). Hence, individual responses to exercise and compensatory mechanisms seem to determine exercise-induced weight loss.
Aerobic exercise on it’s own is not very effective
A recent systematic review and meta-analysis looked at the randomized controlled trials done on isolated aerobic exercise (no dietary intervention) and weight loss (4). The review comprised of 14 trials involving 1847 patients shows that isolated aerobic exercise only results in an average weight loss of 1.6 kg after six months, and an additional 6 months of training doesn’t results in any additional weight reduction. Aerobic exercise, with no dietary intervention, is for most people not an effective weight loss strategy, and it seems that most people respond to the increased energy expenditure by eating more food.
High-intensity intermittent exercise protocols usually involve repeated brief sprinting at an all-out intensity followed by rest or low-intensity exercise. While regular aerobic exercise usually involves longer workouts on a steady-state intensity, HIIE consists of short work and rest periods (5 s to 4 min). Compared to regular aerobic exercise, HIEE seems to be sligthly more effective for someone who wants to lose weight (5).
What about resistance training?
It’s difficult to adjust the intensity and volume of resistance training in order to accurately compare it to aerobic exercise. Heavy resistance training results in muscle growth, but usually a smaller caloric burn during exercise than aerobic training. Since the purpose of resistance exercise usually isn’t to lose weight, it’s no surprise that aerobic exercise seems to be more effective in terms of visceral fat loss (6,7).
While isolated resistance training like weight lifting isn’t associated with any significant reduction in bodyweight, an increase in muscle mass may lead to better metabolic control and increased basal metabolic rate, and resistance exercise is often recommended in the management of obesity, type 2 diabetes and other metabolic disorders (8,9).
All posts in this series on exercise and weight loss
Part 1: Introduction and history
Part 2: How does physical activity affect bodyweight?
Part 3: Physical activity, increased appetite and food intake
Part 4: Exercise and weight gain
Part 5: How much do I lose?
Part 6: Summary, discussion and conclusions