Role of Exercise and Physical Activity in Weight Regulation
The Role of Exercise and Physical Activity in Weight Loss and Maintenance (2013)
- This review explores the role of physical activity (PA) and exercise training (ET) in the prevention of weight gain, initial weight loss, weight maintenance, and the obesity paradox. In particular, we will focus the discussion on the expected initial weight loss from different ET programs, and explore intensity/volume relationships.
- Based on the present literature, unless the overall volume of aerobic ET is very high, clinically significant weight loss is unlikely to occur. Also, ET also has an important role in weight regain after initial weight loss. Overall, aerobic ET programs consistent with public health recommendations may promote up to modest weight loss (~2 kg), however the weight loss on an individual level is highly heterogeneous. Clinicians should educate their patients on reasonable expectations of weight loss based on their physical activity program and emphasize that numerous health benefits occur from PA programs in the absence of weight loss.
Physical activity does not influence obesity risk: time to clarify the public health message (2013)
- Within this new phase of aetiological thinking, however, there has continued to be less clarity about the role of ‘low levels of physical activity’. In this commentary we challenge the theoretical basis for considering reduced energy expenditure in activity as a cause of the obesity epidemic and summarize the empirical data to support that contention.
- From both perspectives – physiological theory as well as observational data and trials as set out below – energy expenditure in activity appears to be playing no role in either causing or moderating the obesity epidemic, suggesting that current guidelines need to be reformulated.
Resistance to exercise-induced weight loss: compensatory behavioral adaptations (2013)
- In many interventions that are based on an exercise program intended to induce weight loss, the mean weight loss observed is modest and sometimes far less than what the individual expected. The individual responses are also widely variable, with some individuals losing a substantial amount of weight, others maintaining weight, and a few actually gaining weight. The media have focused on the subpopulation that loses little weight, contributing to a public perception that exercise has limited utility to cause weight loss.
- The purpose of the symposium was to present recent, novel data that help explain how compensatory behaviors contribute to a wide discrepancy in exercise-induced weight loss. The presentations provide evidence that some individuals adopt compensatory behaviors, that is, increased energy intake and/or reduced activity, that offset the exercise energy expenditure and limit weight loss. The challenge for both scientists and clinicians is to develop effective tools to identify which individuals are susceptible to such behaviors and to develop strategies to minimize their effect.
Obesity, Abdominal Obesity, Physical Activity, and Caloric Intake in US Adults: 1988 to 2010 (2014) Uri Ladabaum, MD, MS, et al
- Obesity and abdominal obesity are associated independently with morbidity and mortality. Physical activity attenuates these risks. We examined trends in obesity, abdominal obesity, physical activity, and caloric intake in US adults from 1988 to 2010.
- Average body mass index (BMI) increased by 0.37% (95% confidence interval [CI], 0.30-0.44) per year in both women and men. Average waist circumference increased by 0.37% (95% CI, 0.30-0.43) and 0.27% (95% CI, 0.22-0.32) per year in women and men, respectively. The prevalence of obesity and abdominal obesity increased substantially, as did the prevalence of abdominal obesity among overweight adults. Younger women experienced the greatest increases.
- The proportion of adults who reported no leisure-time physical activity increased from 19.1% (95% CI, 17.3-21.0) to 51.7% (95% CI, 48.9-54.5) in women, and from 11.4% (95% CI, 10.0-12.8) to 43.5% (95% CI, 40.7-46.3) in men.
- Average daily caloric intake did not change significantly. BMI and waist circumference trends were associated with physical activity level but not caloric intake. The associated changes in adjusted BMIs were 8.3% (95% CI, 6.9-9.6) higher among women and 1.7% (95% CI, 0.68-2.8) higher among men with no leisure-time physical activity compared with those with an ideal level of leisure-time physical activity.
An Unjustified Conclusion from Self-report-based Estimates of Energy Intake (2014)
- To the Editor:
- Although we agree with Ladabaum et al that obesity is a major health problem, we do not believe that any conclusion can be justified from their data as to whether the increase in body weight over the past 2 decades is primarily due to an increase in energy intake or a decrease in energy expenditure. They base their conclusion on their analysis of National Health and Nutrition Examination Survey (NHANES) dataset, indicating that energy intake did not increase during this period while self-reported leisure-time activity decreased. Unfortunately, the NHANES data relied on self-reported energy intake as a measure of energy intake.
- Self-reported energy intake has been shown repeatedly to be an invalid measure of energy intake. Approximately a quarter century ago, investigators using doubly labeled water3 concluded that “current methods of self-reported energy intake are not recommended for use in obesity research.” Last year, Archer et al found that “Across the 39-year history of the NHANES, energy intake data on the majority of respondents (67.3% of women and 58.7% of men) were not physiologically plausible.” A recent study “pooled data from 5 large validation studies of dietary self-report instruments” and found pooled squared correlations between self-reported energy intake and “true” energy intake ranged from 0.04 to 0.10, indicating no more than 10% shared variance. Given this extreme lack of validation of self-reported energy intake as a measure of energy intake, no scientific conclusions can be credibly drawn about energy intake derived from self-reported energy intake measures.
- Because the conclusions reached by Ladabaum et al1 are based on invalid measures of energy intake, the article does not meet reasonable standards for scientific inferences, which contradicts recent trends toward evidence-based medicine and may jeopardize the public’s faith in biomedical science. We are hopeful that we, Ladabaum and colleagues, and others in the field can work together to produce data of the quality that can support scientific conclusions that a problem as important as obesity deserves.
Predictors of fat mass changes in response to aerobic exercise training in women (2015)
- Aerobic exercise training in women typically results in minimal fat loss, with considerable individual variability. We hypothesized that women with higher baseline body fat would lose more body fat in response to exercise training and that early fat loss would predict final fat loss. Eighty-one sedentary premenopausal women (age: 30.7 ± 7.8 years; height: 164.5 ± 7.4 cm; weight: 68.2 ± 16.4 kg; fat percent: 38.1 ± 8.8) underwent dual-energy x-ray absorptiometry before and after 12 weeks of supervised treadmill walking 3 days per week for 30 minutes at 70% of (Equation is included in full-text article.).
- Overall, women did not lose body weight or fat mass. However, considerable individual variability was observed for changes in body weight (-11.7 to +4.8 kg) and fat mass (-11.8 to +3.7 kg). Fifty-five women were classified as compensators and, as a group, gained fat mass (25.6 ± 11.1 kg to 26.1 ± 11.3 kg; p < 0.001). The strongest correlates of change in body fat at 12 weeks were change in body weight (r = 0.52) and fat mass (r = 0.48) at 4 weeks. Stepwise regression analysis that included change in body weight and body fat at 4 weeks and submaximal exercise energy expenditure yielded a prediction model that explained 37% of the variance in fat mass change (R = 0.37, p < 0.001). Change in body weight and fat mass at 4 weeks were moderate predictors of fat loss and may potentially be useful for identification of individuals who achieve less than expected weight loss or experience unintended fat gain in response to exercise training.
Summarized in The New York Times
- So for the new study, which was published last month in The Journal of Strength and Conditioning Research, scientists at Arizona State University in Phoenix recruited 81 healthy but sedentary adult women. All of the women were overweight, based on their body mass index, but some were significantly heavier than others. None had exercised regularly in the past year.
- The women were told that they would be joining a fitness study and would exercise in order to improve their aerobic endurance. The scientists asked the women not to change their eating habits in any way.
- Each of the volunteers visited the physiology lab at the start of the study and the scientists determined their weight, B.M.I., percentage of body fat, current endurance level, and others measures of health and fitness.
- Then each woman began a supervised exercise program designed to be vigorous but manageable by most people, said Glenn Gaesser, a professor of nutrition and health promotion at Arizona State and senior author of the study. The women walked on treadmills at the laboratory three times per week for 30 minutes at a pace that represented about 80 percent of their maximum endurance.
- They continued the program for 12 weeks, with the scientists repeating the original fitness and other tests every month during that time.
- At the end of 12 weeks, the women were all significantly more aerobically fit than they had been at the start. But many were fatter. Almost 70 percent of the women had added at least some fat mass during the program, and several had gained as much as 10 pounds, most of which was from fat, not added muscle.
- A few of the women, though, had lost that much fat or more, and quite a few had remained at the same weight as at the start of the regimen.
- At this point, the researchers returned to the data from the first day of the study, to determine whether any obvious differences existed between the women who subsequently gained or lost weight. “Some past studies of dieting had indicated that women who weigh more at the beginning” of a weight-loss program “tend to lose more weight during the program,” Dr. Gaesser said.
- But the researchers found no correlation in this case between a woman’s weight at the start and end of the study. In fact, the scientists found no connection between any of the original parameters of health and fitness and the women’s responses to the exercise program.
- But looking deeper into their data, they discovered one interesting indicator: Those women who were losing weight after four weeks of exercise tended to continue to lose weight, while the others did not.
- “What that means in practical terms is that someone who wants to lose weight with exercise” should step on the bathroom scale after a month, Dr. Gaesser said. If at that point your weight remains stubbornly unchanged or has increased, “look closely at your diet and other activities,” he said.