Holly R. Wyatt

How much physical activity is enough to prevent unhealthy weight gain? Outcome of the IASO 1st Stock Conference and consensus statement

A consensus meeting was held in Bangkok, 21–23 May 2002, where experts and young scientists in the field of physical activity, energy expenditure and body‐weight regulation discussed the different aspects of physical activity in relation to the emerging problem of obesity worldwide. The following consensus statement was accepted unanimously.

Energy Balance and Obesity

This article describes the interplay among energy intake, energy expenditure, and body energy stores and illustrates how an understanding of energy balance can help us develop strategies to reduce obesity. First, reducing obesity requires modifying both energy intake and energy expenditure, not simply focusing on either alone. Food restriction alone will not be effective in reducing obesity if human physiology is biased toward achieving energy balance at a high energy flux (ie, at a high level of energy intake and expenditure). In previous environments, a high energy flux was achieved with a high level of physical activity, but in todays sedentary environment, it is increasingly achieved through weight gain. Matching energy intake to a high level of energy expenditure will likely be more feasible for most people than restricting food intake to meet a low level of energy expenditure. Second, from an energy balance point of view, we are likely to be more successful in preventing excessive weight gain than in treating obesity. The reason is that the energy balance system shows stronger opposition to weight loss than to weight gain. Although large behavior changes are needed to produce and maintain reductions in body weight, small behavior changes may be sufficient to prevent excessive weight gain. The concept of energy balance combined with an understanding of how the body achieves balance may be a useful framework for developing strategies to reduce obesity rates. Obesity is often considered to be a result of either excessive food intake or insufficient physical activity. There is a great debate about which behavior deserves the most responsibility, but this approach has not yet produced effective or innovative solutions. We believe that obesity can best be viewed in terms of energy balance. The first law of thermodynamics states that body weight cannot change if, over a …

Weight and Metabolic Outcomes After 2 Years on a Low-Carbohydrate Versus Low-Fat Diet: A Randomized Trial

BACKGROUND Previous studies comparing low-carbohydrate and low-fat diets have not included a comprehensive behavioral treatment, resulting in suboptimal weight loss. OBJECTIVE To evaluate the effects of 2-year treatment with a low-carbohydrate or low-fat diet, each of which was combined with a comprehensive lifestyle modification program. DESIGN Randomized parallel-group trial. (ClinicalTrials.gov registration number: NCT00143936) SETTING 3 academic medical centers. PATIENTS 307 participants with a mean age of 45.5 years (SD, 9.7 years) and mean body mass index of 36.1 kg/m(2) (SD, 3.5 kg/m(2)). INTERVENTION A low-carbohydrate diet, which consisted of limited carbohydrate intake (20 g/d for 3 months) in the form of low-glycemic index vegetables with unrestricted consumption of fat and protein. After 3 months, participants in the low-carbohydrate diet group increased their carbohydrate intake (5 g/d per wk) until a stable and desired weight was achieved. A low-fat diet consisted of limited energy intake (1200 to 1800 kcal/d; <or=30% calories from fat). Both diets were combined with comprehensive behavioral treatment. MEASUREMENTS Weight at 2 years was the primary outcome. Secondary measures included weight at 3, 6, and 12 months and serum lipid concentrations, blood pressure, urinary ketones, symptoms, bone mineral density, and body composition throughout the study. RESULTS Weight loss was approximately 11 kg (11%) at 1 year and 7 kg (7%) at 2 years. There were no differences in weight, body composition, or bone mineral density between the groups at any time point. During the first 6 months, the low-carbohydrate diet group had greater reductions in diastolic blood pressure, triglyceride levels, and very-low-density lipoprotein cholesterol levels, lesser reductions in low-density lipoprotein cholesterol levels, and more adverse symptoms than did the low-fat diet group. The low-carbohydrate diet group had greater increases in high-density lipoprotein cholesterol levels at all time points, approximating a 23% increase at 2 years. LIMITATION Intensive behavioral treatment was provided, patients with dyslipidemia and diabetes were excluded, and attrition at 2 years was high. CONCLUSION Successful weight loss can be achieved with either a low-fat or low-carbohydrate diet when coupled with behavioral treatment. A low-carbohydrate diet is associated with favorable changes in cardiovascular disease risk factors at 2 years. PRIMARY FUNDING SOURCE National Institutes of Health.

A randomized, phase 3 trial of naltrexone SR/bupropion SR on weight and obesity-related risk factors (COR-II).

To examine the effects of naltrexone/bupropion (NB) combination therapy on weight and weight‐related risk factors in overweight and obese participants.

Obesity: overview of an epidemic.

The obesity epidemic in the United States has proven difficult to reverse. We have not been successful in helping people sustain the eating and physical activity patterns that are needed to maintain a healthy body weight. There is growing recognition that we will not be able to sustain healthy lifestyles until we are able to address the environment and culture that currently support unhealthy lifestyles. Addressing obesity requires an understanding of energy balance. From an energy balance approach it should be easier to prevent obesity than to reverse it. Further, from an energy balance point of view, it may not be possible to solve the problem by focusing on food alone. Currently, energy requirements of much of the population may be below the level of energy intake than can reasonably be maintained over time. Many initiatives are underway to revise how we build our communities, the ways we produce and market our foods, and the ways we inadvertently promote sedentary behavior. Efforts are underway to prevent obesity in schools, worksites, and communities. It is probably too early to evaluate these efforts, but there have been no large-scale successes in preventing obesity to date. There is reason to be optimistic about dealing with obesity. We have successfully addressed many previous threats to public health. It was probably inconceivable in the 1950s to think that major public health initiatives could have such a dramatic effect on reducing the prevalence of smoking in the United States. Yet, this serious problem was addressed via a combination of strategies involving public health, economics, political advocacy, behavioral change, and environmental change. Similarly, Americans have been persuaded to use seat belts and recycle, addressing two other challenges to public health. But, there is also reason to be pessimistic. Certainly, we can learn from our previous efforts for social change, but we must realize that our challenge with obesity may be greater. In the other examples cited, we had clear goals in mind. Our goals were to stop smoking, increase the use of seatbelts, and increase recycling. The difficulty of achieving these goals should not be minimized, but they were clear and simple goals. In the case of obesity, there is no clear agreement about goals. Moreover, experts do not agree on which strategies should be implemented on a widespread basis to achieve the behavioral changes in the population needed to reverse the high prevalence rates of obesity. We need a successful model that will help us understand what to do to address obesity. A good example is the recent HEALTHY study. This comprehensive intervention was implemented in several schools and aimed to reduce obesity by concentrating on behavior and environment. This intervention delivered most of the strategies we believe to be effective in schools. Although the program produced a reduction in obesity, this reduction was not greater than the reduction seen in the control schools that did not receive the intervention. This does not mean we should not be intervening in schools, but rather that it may require concerted efforts across behavioral settings to reduce obesity. Although we need successful models, there is a great deal of urgency in responding to the obesity epidemic. An excellent example is the effort to get menu labeling in restaurants, which is moving rapidly toward being national policy. The evaluation of this strategy is still ongoing, and it is not clear what impact it will have on obesity rates. We should be encouraging efforts like this, but we must evaluate them rigorously. Once we become serious about addressing obesity, it will likely take decades to reverse obesity rates to levels seen 30 years ago. Meanwhile, the prevalence of overweight and obesity remains high and quite likely will continue to increase.

The role of physical activity in producing and maintaining weight loss

The majority of randomized, controlled trials (RCTs) show only modest weight loss with exercise intervention alone, and slight increases in weight loss when exercise intervention is added to dietary restriction. In most RCTs, the energy deficit produced by the prescribed exercise is far smaller than that usually produced by dietary restriction. In prospective studies that prescribed high levels of exercise, enrolled individuals achieved substantially greater weight loss—comparable to that obtained after similar energy deficits were produced by caloric restriction. High levels of exercise might, however, be difficult for overweight or obese adults to achieve and sustain. RCTs examining exercise and its effect on weight-loss maintenance demonstrated mixed results; however, weight maintenance interventions were usually of limited duration and long-term adherence to exercise was problematic. Epidemiologic, cross-sectional, and prospective correlation studies suggest an essential role for physical activity in weight-loss maintenance, and post hoc analysis of prospective trials shows a clear dose–response relationship between physical activity and weight maintenance. This article reviews the role of physical activity in producing and maintaining weight loss. We focus on prospective, RCTs lasting at least 4 months; however, other prospective trials, meta-analyses and large systematic reviews are included. Limitations in the current body of literature are discussed.

Pedometer-Measured Physical Activity and Health Behaviors in U.S. Adults

UNLABELLED U.S. adults may have lower levels of ambulatory physical activity compared with adults living in other countries. PURPOSE The purpose of this study was to provide descriptive, epidemiological data on the average number of steps per day estimated to be taken by U.S. adults and to identify predictors of pedometer-measured physical activity on the basis of demographic characteristics and self-reported behavioral characteristics. METHODS The America On the Move study was conducted in 2003. Individuals (N = 2522) aged 13 yr and older consented to fill out a survey, including 1921 adults aged 18 yr and older. Valid pedometer data were collected on 1136 adults with Accusplit AE120 pedometers. Data were weighted to reflect the general U.S. population according to several variables (age, gender, race/ethnicity, education, income, level of physical activity, and number of 5- to 17-yr-old children in the household). Differences in steps per day between subgroups were analyzed using unpaired t-tests when only two subgroups were involved or one-way ANOVA if multiple subgroups were involved. RESULTS Adults reported taking an average of 5117 steps per day. Male gender, younger age, higher education level, single marital status, and lower body mass index were all positively associated with steps per day. Steps per day were positively related to other self-reported measures of physical activity and negatively related to self-reported measures on physical inactivity. Living environment (urban, suburban, or rural) and eating habits were not associated with steps per day. CONCLUSIONS In the current study, men and women living in the United States took fewer steps per day than those living in Switzerland, Australia, and Japan. We conclude that low levels of ambulatory physical activity are contributing to the high prevalence of adult obesity in the United States.

From instinct to intellect: the challenge of maintaining healthy weight in the modern world.

The global obesity epidemic is being driven in large part by a mismatch between our environment and our metabolism. Human physiology developed to function within an environment where high levels of physical activity were needed in daily life and food was inconsistently available. For most of mankind’s history, physical activity has ‘pulled’ appetite so that the primary challenge to the physiological system for body weight control was to obtain sufficient energy intake to prevent negative energy balance and body energy loss. The current environment is characterized by a situation whereby minimal physical activity is required for daily life and food is abundant, inexpensive, high in energy density and widely available. Within this environment, food intake ‘pushes’ the system, and the challenge to the control system becomes to increase physical activity sufficiently to prevent positive energy balance. There does not appear to be a strong drive to increase physical activity in response to excess energy intake and there appears to be only a weak adaptive increase in resting energy expenditure in response to excess energy intake. In the modern world, the prevailing environment constitutes a constant background pressure that promotes weight gain. We propose that the modern environment has taken body weight control from an instinctual (unconscious) process to one that requires substantial cognitive effort. In the current environment, people who are not devoting substantial conscious effort to managing body weight are probably gaining weight. It is unlikely that we would be able to build the political will to undo our modern lifestyle, to change the environment back to one in which body weight control again becomes instinctual. In order to combat the growing epidemic we should focus our efforts on providing the knowledge, cognitive skills and incentives for controlling body weight and at the same time begin creating a supportive environment to allow better management of body weight.

The obesity epidemic.

Obesity has reached epidemic proportions in the United States, with 35.1% of adults being classified as obese. Obesity affects every segment of the US population and continues to increase steadily, especially in children. Obesity increases the risk for many other chronic diseases, including diabetes mellitus, cardiovascular disease, and nonalcoholic fatty liver disease, and decreases overall quality of life. The current US generation may have a shorter life expectancy than their parents if the obesity epidemic is not controlled, and there is no indication that the prevalence of obesity is decreasing. Because of the complexity of obesity, it is likely to be one of the most difficult public health issues our society has faced.

Small changes in dietary sugar and physical activity as an approach to preventing excessive weight gain: the America on the Move family study.

OBJECTIVES. The intent of this study was to evaluate whether small changes in diet and physical activity, as promoted by the America on the Move initiative, could prevent excessive weight gain in overweight children. METHODS. In this family-intervention study, the America on the Move small-changes approach for weight-gain prevention was evaluated in families with at least 1 child (7–14 years old) who was overweight or at risk for overweight. These children were the primary target of the intervention, and parents were the secondary target. Families were randomly assigned to either the America on the Move group (n = 100) or the self-monitor–only group (n = 92). Families who were assigned to the America on the Move group were asked to make 2 small lifestyle changes: (1) to walk an additional 2000 steps per day above baseline as measured by pedometers and (2) to eliminate 420 kJ/day (100 kcal/day) from their typical diet by replacing dietary sugar with a noncaloric sweetener. Families who were assigned to the self-monitor group were asked to use pedometers to record physical activity but were not asked to change their diet or physical activity level. RESULTS. During a 6-month period, both groups of children showed significant decreases in BMI for age. However, the America on the Move group compared with the self-monitor group had a significantly higher percentage of target children who maintained or reduced their BMI for age and, consistently, a significantly lower percentage who increased their BMI for age. There was no significant weight gain during the 6-month intervention in parents of either group. CONCLUSIONS. The small-changes approach advocated by America on the Move could be useful for addressing childhood obesity by preventing excess weight gain in families.