|Physical Activity, Weight Loss and Weight Regain
Len Kravitz, Ph.D.
Donnelly, J.E., Blair, S.N., Jakicic, J.M., Manore, M.M., Rankin, J.W., & Smith, B.K. (2009). Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults, 41(2), 459-469.
The new ACSM position stand on physical activity intervention strategies for weight loss reflects an update from the previous position statement, synthesizing all published data-based research from 1999 to the present. This compilation of physical activity and weight management research includes individuals &Mac179;18 years of age, although the authors note there is a need for more weight loss studies with older populations (&Mac179;65 years). Investigations with subjects who have disorders such as cardiovascular disease, hypertension, and type 2 diabetes were included because these health troubles are reflective of the overweight/obese U.S. society. The quantification of exercise intensity is presented in the form of METS (meaning metabolic equivalents). One met is the equivalent of 3.5 ml/kg/min and is considered a resting level of oxygen consumption. Light-intensity activity is quantified as 1.1 to 2.9 METS with moderate-intensity at 3.0 to 5.9 METS and vigorous activity at &Mac179; 6 METS.
Overweight and Obesity
Presently 66.3% of U.S. citizens are either overweight (BMI = 25-29.9 kg/m2) and/or obese (BMI &Mac179; 30 kg/m2). Weight loss in overweight/obese persons of as little as 3% to 5% of body weight (although 10% reduction is encouraged) has shown improvements in high-density lipoproteins (the good cholesterol), glucose metabolism, a decrease in triglycerides (blood fats) and other risk factors of cardiovascular disease (Donnelly et al., 2009). However, despite these impressive health benefits of weight loss, it is clear that the U.S. is not going to reach its Healthy People 2010 initiative for reducing the prevalence of obesity (see Side Bar 1 for health initiatives and weight loss campaigns).
Weight Maintenance Defined and the Prevention of Weight Gain
In the new ACSM position stand, Donnelly et al. (2009) define weight maintenance as a <3% change in body weight, where as an increase in >5% change in body weight is considered a clinically significant change. The term clinical' infers involving a medical observation, treatment, practice or diagnosis. It is clear from all of the research and medical/scientific organizations (Centers for Disease Control, ACSM, AHA and AMA) that more physical activity is needed for most persons. The recent research indicates that moderately vigorous physical activity of 150 to 250 minutes per week at an energy equivalent of ~1200 to 2,000 kilocalories per week (about 12 to 20 miles per week of jogging or running) will be sufficient in preventing weight gain greater than 3%.
How Much Physical Activity Is Needed for Clinically Significant Weight Loss?
It is recognized that most studies showing clinically significant weight loss (5% of body weight) demonstrate this with energy restriction (i.e., eating fewer calories) combined with physical activity to create a larger negative energy balance (i.e., more calories expended than consumed). That noted, the research denotes that physical activity <150 minutes/week has a minimal effect on weight loss. Physical activity >150 minutes/week usually results in modest weight loss (defined as ~2-3 kg), with physical activity between 225 and 420 minutes/week resulting in the greatest weight loss (5 to 7.5 kg).
What About Weight Regain After Weight Loss?
It appears that most individuals are capable of losing weight with the long-standing challenge being how to maintain this reduced body weight. Consistent physical activity is the best predictor of sustained weight management after weight loss. And, when it comes to preventing weight gain, 'more is better' as Donnelly et al. (2009) report that some research specifies that individuals who lost >10% of their body weight in 24 months were participating in 275 minutes of physical activity a week. However, due to research methodology design flaws, currently there is no definitive answer how much exercise is needed to prevent weight regain. Minimally, Donnelly and colleagues suggest it is likely to be approximately 60 minutes per day (about 4 miles/day) at a moderate intensity.
No More Confusion: Lifestyle Approaches vs. Lifestyle Forms of Physical Activity
Lifestyle forms of physical activity include physical activity that is not an organized approach to exercise. This comprises spontaneous physical activity an individual does during the day (i.e., walking from the car to a store; walking to the chair at a theatre; walking in a grocery store; walking onto an airplane, etc.). Contrariwise, lifestyle approaches to physical activity include participation in organized exercise, leisure time physical activity, occupational physical activity, household physical activity and physical activity for commuting. Numerous studies point out that lifestyle approaches to increased physical activity are quite effective for preventing initial weight gain. Unfortunately, most adults spend most of their time sitting. The more active a person is, the less likely he/she will become obese.
How effective is 'Diet Only' versus 'Diet plus Exercise' for Weight Loss?
Most studies demonstrate that when diet (caloric restriction) and physical activity are combined in a weight management program, encouraging results in weight loss occur. Donnelly and colleagues (2009) explain that a weight loss program design may create an energy deficit (e.g., 500 to 1500) composed of exercise (e.g., 250 kilocalories/day) and caloric restriction (e.g., 250 kilocalories/day) for the daily caloric deficit total (500 kilocalories in this example). In studies where investigators introduce an energy deficit of 700 to 1000 kilocalories per day, 'diet only' and 'diet plus exercise' result in similar losses. Donnelly explains that this is due to metabolic adaptations that diminish any additive effect of energy expenditure from physical activity on weight loss. However, in investigations where the energy deficit is 500-700 kilocalories/day, the 'diet plus exercise' group is about 20% greater than the 'diet only' intervention.
Where Does Resistance Exercise Fit in the Weight Loss Picture?
Consistent resistance training provides numerous health-related benefits, including increases in insulin sensitivity, higher levels of HDL-C (the healthy cholesterol), reductions in blood glucose levels, lower levels of LDL-C (the bad cholesterol) and cardiovascular disease risk reduction. The increase in muscle mass from resistance exercise has been shown to elevate resting metabolic rate in some persons. Some resistance training programs elicit an increased fat oxidation (burning) after the workout (as the body uses additional energy to restore cell processes to homeostasis). Exercise programs combining aerobic training and resistance exercise exhibit superior results in weight and fat loss. In 'diet plus resistance training' programs, the addition of resistance training promotes the preservation and/or increase in fat-free mass.
Let's Put It Together
As exercise professionals, the evidence continues to mount that our first goal is to get clients active, with our continuing efforts to get students doing more endurance exercise at a more challenging intensity. Regular resistance training is a must for the maintenance and/or increase of fat-free mass. Donnelly et al. (2009) recommend 250 to 300 minutes/week (~2000 kilocalories/week) of moderate intensity exercise for greater weight loss and prevention of weight gain. We can do it!
Side Bar 1. Initiatives and Campaigns to Reduce Obesity
A. Healthy People 2010
Healthy People 2010 is a declaration of national health objectives which has identified the most significant preventable threats to health and has established national goals to reduce these threats.
B. Steps to a HealthierUS Initiative
The Steps to a HealthierUS Cooperative Agreement Program (Steps Program) is a national, multi-level program that is focused on chronic disease prevention in communities across the United States and improving people's lives.
C. Make Your Calories Count
This is a new Web-based interactive on-line learning program that is designed to help consumers understand and use the nutrition facts label to plan a healthful diet.
D. We Can!
We Can! or "Ways to Enhance Children's Activity & Nutrition" is a national program designed for families and communities to help children maintain a healthy weight.