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New Guidelines for Physical Activity Intervention for Weight Loss
Posted: Wednesday, March 11, 2009
The American College of Sports Medicine (ACSM) has updated its guidelines for appropriate physical activity (PA) intervention strategies for weight loss and prevention of weight regain in adults.
The Position Stand updates the 2001 ACSM recommendations. The latter document discussed identifying adults needing weight loss, the magnitude of weight loss recommended, dietary strategies, the use of resistance exercise, the use of pharmacotherapy, behavioral techniques, and other topics.
"The purpose of the current update was to focus on new information that has been published after 1999, which may indicate that increased levels of ... PA may be necessary for prevention of weight gain, for weight loss, and prevention of weight regain compared to those recommended in the 2001 Position Stand," write Joseph E. Donnelly, EdD, and colleagues from the ASCM. "In particular, this update is in response to published information regarding the amount of PA needed for weight management found in the National Weight Control Registry and by the Institute of Medicine. This update was undertaken for persons older than 18 yr who were enrolled in PA trials designed for prevention of weight gain (i.e., weight stability), for weight loss, or prevention of weight regain."
Guidelines regarding weight control are needed because more than 66% of the adult population are overweight or obese, conditions which are associated with a variety of chronic diseases. Although guidelines of the National Heart, Lung, and Blood Institute recommend a 10% reduction in weight for those who are obese, much evidence supports a lowered health risk with 3% to 5% weight loss.
To prevent weight gain, to lose weight, and to prevent weight regain after weight loss, PA is recommended as a component of weight management. Light-intensity activity is defined as 1.1 to 2.9 metabolic equivalents, moderate-intensity activity as 3.0 to 5.9 metabolic equivalents, and vigorous activity as 6 or more metabolic equivalents.
Although the 2001 ACSM guidelines recommended a minimum of 150 minutes per week of moderate-intensity PA for overweight and obese adults to improve health and 200 to 300 minutes per week for long-term weight loss, the updated guidelines suggest that moderate-intensity PA between 150 and 250 minutes per week is effective to prevent weight gain but will provide only modest weight loss.
Clinically significant weight loss has been reported with greater amounts of PA (> 250 minutes per week). In studies that use moderate but not severe diet restriction, weight loss was improved by moderate-intensity PA between 150 and 250 minutes per week. After weight loss, weight maintenance is improved with PA of more than 250 minutes per week, according to findings of cross-sectional and prospective studies, but there have been no well-designed, randomized controlled trials to determine whether PA is effective to prevent weight regain after weight loss.
Although resistance training does not increase weight loss, it may increase fat-free mass and loss of fat mass while lowering health risk. Available data suggest that endurance PA or resistance training reduces health risk even without weight loss. Evidence to date is insufficient to determine whether PA prevents or ameliorates harmful changes in the risk for chronic disease during periods of weight gain.
Few studies to date have enrolled adults older than 65 years, but this is an important population to evaluate because of concerns that weight loss in older adults may cause loss of fat-free mass and potential bone loss. The position stand reviews the available evidence as it applies to the general population, while pointing out that individuals vary in their response to PA for prevention of weight gain, for weight loss, and for weight maintenance.
Although the review did not include studies of individuals with comorbid conditions that acutely affect weight, such as AIDS and type 1 diabetes, or pharmacotherapy trials, it did include trials enrolling individuals using medication for comorbid diseases, such as hypertension, cardiovascular disease, and type 2 diabetes.
Specific clinical recommendations, and their accompanying level of evidence rating, are as follows:
* For prevention of weight gain in most adults, PA of 150 to 250 minutes per week, with an energy equivalent of 1,200 to 2,000 kcal/week, will prevent weight gain of more than 3% (level of evidence, A).
* There is a dose-response effect of PA on weight loss, with PA of less than 150 minutes per week resulting in minimal weight loss, PA of more than 150 minutes per week in modest weight loss of approximately 2 to 3 kg, and PA of more than 225 to 420 minutes per week leading to weight loss of 5 to 7.5 kg (level of evidence, B).
* To maintain weight after weight loss, some studies suggest that PA of approximately 200 to 300 minutes per week will help minimize weight regain, although "more is better." To date, no well-designed, sufficiently powered, energy-balance studies provide evidence concerning the amount of PA needed to prevent weight regain after weight loss (level of evidence, B).
* Lifestyle PA, which is an ambiguous term that should be better defined to assess available evidence in the literature, may help counteract the small energy imbalance ultimately leading to obesity in most adults (level of evidence, B).
* If diet restriction is modest but not if diet restriction is severe, PA will increase weight loss (level of evidence, A).
* Resistance training is ineffective for weight loss with or without diet restriction, according to limited research evidence. However, some limited data suggest that resistance training enhances gain or maintenance of lean mass and loss of body fat during energy restriction. Furthermore, resistance training may also ameliorate risk factors for chronic disease, such as low high-density lipoprotein cholesterol levels, high low-density lipoprotein cholesterol levels, insulin sensitivity, and blood pressure (level of evidence, B).
"On the basis of the available scientific literature, the ACSM recommends that adults participate in at least 150 min/wk of moderate-intensity PA to prevent significant weight gain and reduce associated chronic disease risk factors," the guidelines authors write. "It is recommended that overweight and obese individuals participate in this level of PA to elicit modest reductions in body weight. However, there is likely a dose effect of PA, with greater weight loss and enhanced prevention of weight regained with doses of PA that approximate 250 to 300 min/wk (approximately 2,000 kcal/wk) of moderate intensity PA."
The guidelines authors note that these recommendations are consistent with those of the US Department of Health and Human Services Physical Activity Guidelines for Americans.
Source: Diabetes In Control: Med Sci Sports Exerc. 2009;41:459-471.
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