Move to lose? Physical activity and weight management
It is well known that physical activity is important for managing weight, but it’s not clear to most people which aspects of weight loss is impacted by it. Does it help with both losing weight and maintaining that weight loss? Which is better resistance training or aerobic training? Would it be better to just restrict calories and forego the rigors of engaging in physical activity? To address these questions and more, we turn to the American College of Sports Medicine (ASCM); arguably the most reputable exercise science research body in North America and perhaps the world. The ACSM has a position paper entitled: Appropriate Physical Activity Intervention Strategies for Weight Loss and Prevention of Weight Regain for Adults. Below is a summary of that position paper.
Maintaining one's current weight
Physical activity will assist with maintaining one's current weight (preventing further weight gain). Moderately vigorous physical activity is likely sufficient to prevent further gains in weight. There is data to suggest that even those who exercised less than 150 minutes/week had gained less weight than sedentary individuals. The amount of physical activity recommended would be:
- 150 - 250 minutes/week (20 - 35 minutes/d)
- energy expenditure of: 1200 - 2000 kcal/week (171 - 285 kcal/d)
Physical activity and clinically significant weight loss
It seems that the more physical activity one does, the more weight they are likely to lose. For example:
- less than 150 minutes a week of physical activity results in minimal weight loss
- Greater than 150 minutes of physical activity / week results in modest weight loss of 2 - 3 kg. This is equivalent to 21 mins/d to lose 4.4 - 6.6 lbs.
- 225 - 420 mins/week (32 - 60 mins/d) may result in 5 - 7.5 kg (11 - 16.5 lbs) of weight loss.
These conclusions were drawn from studies ranging from 12 weeks to 16 and 18 months in duration.
Preventing gaining weight again after losing it
Physically activity is considered to be a necessity for weight maintenance. It's perhaps the best predictor for whether an individual will keep maintaining their weight loss. However, the specific amount is yet uncertain. But there are some interesting findings that help provide some guidance:
- 275 minutes/week (~1500 kcal/week) resulted in greater maintenance of weight loss after 24 months. This would amount to 30 minutes/d and 215 kcals/d of physical activity.
- Averaging approximately 2317 kcal/week (331 kcal/d) had greater sustained weight loss after 18 months.
- Likely, ~60 minutes/d of an exercise such as walking (~4 miles/d) at a moderate intensity may be sufficient to maintain weight.
Physical activity in combination with diet
When the dietary restriction is severe, physical activity does not seem to add any further benefit. However, when the dietary restriction is modest, physical activity + diet is superior to diet alone. One researcher concluded that physical activity combined with diet results in 20% greater weight loss vs diet alone (13 kg vs 9 kg) over the course of 10 weeks to over a year.
Resistance training and weight loss
Without a modification in diet, resistance training (RT) on its own does not result in large amounts of energy expenditure. However, combining resistance training and restricting energy intake is superior to just energy restriction on its own. RT will increase muscle mass and the energy expenditure over a 24 hr period. It may perhaps reduce body fat but the evidence is contradictory.
Resistance training combined with aerobic training
Resistance training combined with aerobic training appears to be superior for reducing body weight and fat compared to just aerobic exercise.
Conclusion from the paper
"Moderate-intensity PA of 150 to 250 minutes/week with an energy equivalent of ~1200 to 2000 kcal/week seems sufficient to prevent weight gain greater than 3% in most adults and may result in modest weight loss. PA without diet restriction generally provides modest weight loss; ... PA combined with diet restriction provides a modest addition of weight loss compared to diet alone, and this additive effect is diminished as the level of diet restriction increases. .. The effects of resistance training for prevention of weight gain are largely unknown owing to lack of available literature. Resistance training does not seem to be an effective means for weight loss, but is associated with numerous other health benefits including decreases in many chronic disease risk factors and increases in fat-free mass and decreases in fat mass. Weight maintenance compared to weight gain seems to protect against an increase in chronic disease risk factors..." (p. 467)
Donnelly JE et al. American College of Sports Medicine Position Stand. Appropriate Physical Activity Intervention Strategies for Weight Loss and Prevention of Weight Regain for Adults. Medicine & Science in Sports & Exercise. 2009; Feb 41(2): 459 - 471
Click here for full text of the ACSM position stand