John C. Peters

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 …

THE VARIABILITY OF YOUNG CHILDREN'S ENERGY INTAKE

Abstract Background. Research conducted in the 1930s showed that, given nutritious choices, children can select an adequate diet without adult supervision. Paradoxically, children grew well and were healthy despite patterns of intake at individual meals that were unpredictable and highly variable. Methods. To investigate in more detail the energy intake of young children, we measured 24-hour food intake for 15 children, from two to five years of age, on six days. For each of the six days of the study, coefficients of variation were calculated for each child for each of the six meals and snacks (breakfast, lunch, dinner, and morning, afternoon, and evening snacks) and for total daily energy intake. Results. The childrens intake at individual meals was highly variable, but total daily energy intake was relatively constant for each child. The mean coefficient of variation for each childs energy intake at individual meals was 33.6 percent; in contrast, the mean coefficient of variation for each childs tota...

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.

A Colorado statewide survey of walking and its relation to excessive weight.

INTRODUCTION There is an urgent need to increase the physical activity in the population. Small-scale success has been achieved in programs like Colorado on the Move (COM), an obesity prevention program using electronic pedometers. METHODS To provide baseline information for COM, this first-ever statewide survey of walking was conducted with 1098 individuals. The weighted mean BMI was 25.3 +/- 0.18 kg x m(-2), and mean age was 44 +/- 0.42 yr of age. Subjects participated in a short telephone interview and then were sent a pedometer to wear for four consecutive days. A total of 742 of the 1098 subjects completed the pedometer phase. RESULTS The average adult in Colorado reported taking 6804 steps per day. About 33% reported taking fewer than 5000 steps per day, and only 16% reported taking 10,000 or more steps per day. Steps per day increased with other self-reported measures of physical activity (P = 0.0001) and decreased with self-reported inactivity (P = 0.0001). Significant determinants of steps per day included increasing age (negative, P = 0.001), marital status (positive for single status, P = 0.05), income (positive for incomes of dollar 25,000 to dollar 99,000, P = 0.003), and increasing BMI (negative for BMI > or = 30 kg x m(-2), P = 0.000). Obese individuals (BMI > or = 30 kg x m(-2)) walked about 2000 fewer steps per day than normal-weight individuals. These results provide the first population data on current walking levels, on how this relates to self-reported physical activity, and on determinants of walking. Results also provide a baseline level of walking for future evaluation of COM. CONCLUSION Increasing steps per day appears to be a good target to use in interventions to increase physical activity. Even in Colorado, one of the leanest states, very low levels of physical activity are seen in much of the population.

Thermogenesis in humans during overfeeding with medium-chain triglycerides

To test whether excess dietary energy as medium-chain triglycerides (MCT) affects thermogenesis differently from excess dietary energy as long chain triglycerides (LCT), ten male volunteers (ages 22 to 44) were overfed (150% of estimated energy requirement) liquid formula diets containing 40% of fat as either MCT or LCT. Each patient was studied for one week on each diet in a double-blind, crossover design. Resting metabolic rate (RMR) did not change during either week of overfeeding. The thermic response to food (TEF) was greater on day 1 following a meal (1,000 kcal) containing MCT than following an isocaloric meal containing LCT (8 +/- .8% v 5.8 +/- .8% of ingested energy; P less than .05). Moreover, the TEF observed after a 1,000 kcal meal containing MCT increased significantly to 12% (+/- 1.3%) overfeeding. The TEF of the 1,000 kcal meal containing LCT was unchanged by five days of LCT overfeeding (6.6 +/- 1.0% of ingested energy). Energy expenditure during a 20-hour continuous enteral infusion of the diet on day 7 was also significantly higher with the MCT diet than with the LCT diet (15.7 +/- 1.7% v 7.3 +/- .9% of ingested energy; P less than .05). Our results demonstrate that excess dietary energy as MCT stimulates thermogenesis to a greater degree than does excess energy as LCT. This increased energy expenditure, most likely due to lipogenesis in the liver, provides evidence that excess energy derived from MCT is stored with a lesser efficiency than is excess energy derived from dietary LCT.

Using the Energy Gap to Address Obesity: A Commentary

The global obesity pandemic has arisen from small imbalances in energy intake and expenditure that have accumulated over time. For primary obesity prevention, the energy gap in the U.S. is less than 100 kcal/day for 90% of the population, meaning that relatively small changes in energy intake and expenditure adding up to 100 kcal/day could arrest excess weight gain in most people. Preventing further weight gain in the population could substantially reduce the prevalence of obesity within one generation. The energy gap is even smaller in other countries that have made similar analyses. The energy gap for weight reduction and maintenance (i.e., obesity treatment) is much larger than 100 kcal/day owing to the increased energy demands of maintaining a larger body. Thus, the magnitude of behavioral changes required to restore the current population to normal weight is much larger than that required to prevent further weight gain. At this point in time, efforts to create and sustain such large changes in behavior, either at the individual or population level, have been unsuccessful. Focusing solely on trying to address the large energy gap associated with obesity treatment seems unsatisfactory and unhelpful as it both overlooks the tangible progress that could be made against preventing primary weight gain and it seems tantamount to suggesting that attempts to deal with obesity should only be initiated once it is established. The notion that the obesity pandemic is exclusively due to increased food intake is also not helpful in finding a solution. While it is certainly easier to find a villain to blame for increased food intake (the food industry) than it is to assign ownership for sedentariness (e.g., progress, technology), it ignores the evidence that increased levels of physical activity are essential for effectively balancing energy intake and expenditure at a healthy weight. In order to restore conditions under which human physiology evolved and developed mechanisms for balancing energy intake and expenditure, it will require both finding effective ways to assure a reasonable level of daily physical activity AND reducing energy intake. At this time, small changes in both intake and expenditure may be sufficient to prevent further population weight gain and support energy balance at a healthy weight. It will take a concerted effort by both public and private interests to accomplish even this goal. Restoring normal body weights among those already obese would likely require more dramatic intervention including pharmacological and surgical treatment. A small changes approach must be included in public health strategies and in public policies to address obesity.

Obesity Treatment: Can Diet Composition Play a Role?

Treatments for obesity involve a weight-reduction phase and a subsequent maintenance phase. To assess the role of diet composition in the treatment of obesity, it is necessary to evaluate its effect on both phases. During weight reduction, one must consider whether diet composition affects the amount, composition, or rate of weight loss for a given degree of negative energy balance. In the maintenance phase, one must consider whether diet composition affects the successful maintenance of a reduced body weight. This review addresses these questions and provides some basis for understanding the mechanisms by which diet composition can influence body weight regulation. Before reviewing the experimental data, we review some basic principles governing body weight regulation. Energy Balance Equation To maintain a stable body weight, energy intake must be balanced by an equivalent amount of energy expenditure, as shown by the following equation: Ein Eout = Estored in which Ein represents energy intake, Eout represents energy expenditure, and Estored represents energy stored in the body (the difference between energy intake and expenditure). All components of this equation can be characterized in terms of the amount and composition of energy. The macronutrient composition of ingested food becomes particularly important when one considers that maintenance of constant body weight and composition requires not only that energy intake equal energy expenditure but that, on average, the intakes of the major nutrients comprising body tissuesprotein, carbohydrate, and fatare balanced by equivalent oxidation of each. Failure to achieve this nutrient balance results in changes in body stores of protein, carbohydrate, or fat. Significant changes in these compartments as a result of cumulative effects over time can influence metabolic processes (for example, the rate of fatty acid oxidation), which can, in turn, alter the proportions of metabolic fuels oxidized [13]. Furthermore, alterations in the fuel mixture can affect the steady-state body weight and body composition that is reached under a given set of dietary conditions [24]. Diet Composition, Energy Balance, and Nutrient Balance In this section, we discuss the effect of diet composition on energy intake, energy expenditure, and nutrient balance in general terms and under conditions of weight reduction. Effects on Energy Intake Most research on the effects of diet composition on food intake has focused on the fat and carbohydrate components of the diet, whereas protein has been less studied. Studies in rodents and humans have shown that voluntary energy intake tends to increase, with increases in the proportion of dietary energy supplied by fat [57]. Although some reports have indicated that diets high in sweet carbohydrates (for example, sucrose) elevate long-term energy intake in animals [8], a similar long-term effect has not been described in humans. High levels of protein (> 25% of calories) have a suppressive effect on energy intake in animals [9]. In humans, high-protein loads acutely reduce subsequent energy intake relative to low-protein foods [10]. The effects of protein are probably of limited importance in humans because protein makes up a small and relatively constant proportion (10% to 15%) of calories [11, 12]. Effects on Energy Expenditure and Nutrient Oxidation Energy expenditure (Eout) involves several factors, as shown by the following equation: Eout = RMR + EEACT + TEF in which RMR is the resting metabolic rate, EEACT is the energy expenditure associated with physical activity, and TEF is the thermic effect of food. Diet composition has not been shown to directly influence resting metabolic rate, which accounts for more than 50% of total daily energy expenditure in sedentary persons [13]. Because the main determinant of resting metabolic rate is fat-free mass (with fat mass as a lesser determinant) [13], diet composition may have secondary effects on resting metabolic rate through long-term effects on body composition. Studies in humans have yielded no data suggesting that diet composition can directly affect the energy expended in physical activity. To calculate the energy expended in physical activity, both the amount and energy cost of physical activity must be considered. Unlike for resting metabolic rate, the factors that can explain the interpatient variation in amount and energy cost of physical activity are not well understood. Little is known about the influence of diet composition on the amount of physical activity; however, this area deserves further study. The third component of energy expenditure is the thermic effect of food, which represents the energy expended in digesting, absorbing, interconverting, and storing ingested nutrients. Overall, the magnitude of the thermic effect of food is small (about 6% to 10% of total ingested energy) and is less than the error involved in measuring food intake under outpatient conditions. Both the amount [14] and composition [15, 16] of food can affect the thermic effect of food; however, increasing the proportion of dietary fat from 20% to 60% of total calories while keeping the proportion of protein constant does not produce a measurable difference in energy expenditure during a 24-hour period [17]. Effects on Nutrient Balance Nutrient balance represents the difference between the intake of a given energy-yielding nutrient and its oxidation during a specified time period. In the case of fat, a person is in fat balance when the oxidation of fat by the body is equal to the intake of fat from the diet. If this condition is not met, fat is either gained or lost. A similar situation is true for the other major dietary energy sourcesprotein and carbohydrate. Recent work has shown that the oxidation of protein and carbohydrate is closely tied to their intake, whereas fat oxidation is not as tightly correlated with intake [1821]. Thus, both protein and carbohydrate are actively metabolized after ingestion, and the balance of these nutrients is closely maintained. Fat oxidation, conversely, is not actively driven by fat intake but occurs passively as the difference between total energy expenditure and the oxidation of protein and carbohydrate [22]. Because fat intake does not promote its own oxidation, maintenance of fat balance requires that other factors promoting fat oxidation, such as negative energy balance or exercise, must compensate for the fat consumed in the diet. The tendency for persons to overconsume energy when the diet is rich in fat and the prevalence of sedentary lifestyles in Western societies undoubtedly contribute to the high incidence of obesity in these populations. Influence of Obesity Treatment on Energy and Nutrient Balance By definition, the treatment of obesity involves the creation of a negative energy balance, a condition in which energy expenditure exceeds energy consumption. When this condition is achieved, body energy stores are consumed to sustain metabolic processes, and weight loss ensues. Because a negative energy balance is required for successful obesity treatment, we should consider the effects of this physiologic state on the main components of the energy balance equation described earlier and on nutrient balance. When a negative energy balance is achieved through reduced energy intake, the primary and short-term effect on energy expenditure is a reduction in the thermic effect of food proportional to the reduction in energy intake. As caloric restriction continues, the resulting decrease in body mass is accompanied by a reduction in the resting metabolic rate. The energy expended in physical activity also decreases because the energy cost of movement is less at lower body masses [23]. Exercise in conjunction with caloric restriction is frequently used in obesity treatment programs. The primary effect of exercise is to increase energy expenditure during periods of activity. Physical activity does not appear to have significant effects on the thermic effect of food [24]. When combined with food restriction, exercise may preserve fat-free mass, but the effect is small and is unlikely to have a measurable effect on the decrease in resting metabolic rate that accompanies weight reduction [25]. The effect of a negative energy balance on nutrient oxidation and balance is necessarily dominated by the metabolic condition associated with energy deprivation. Regardless of how the negative energy balance is achieved, the body is forced into a negative protein and fat balance. This condition occurs because fat is the major stored fuel oxidized under hypocaloric conditions (fasting or dieting) and because some net protein oxidation is necessary due to the loss of tissue supporting the lost fat. In addition, protein loss occurs due to the essential role of protein in providing amino acids that can be converted to glucose. Carbohydrate balance may be negative initially after the imposition of a negative energy balance, but a new steady-state balance (possibly at a reduced level of body carbohydrate stores) is reached within several days and is maintained. Carbohydrate will remain the preferred fuel for several important tissues (for example, brain and formed blood elements) even during a complete fast, and the body is equipped to provide this fuel by converting amino acids into glucose through the process of gluconeogenesis. Diet Composition and Obesity Treatment Diet composition is one of many variables that can influence the short- and long-term outcome of an obesity treatment program. In the next section, we address some of the most commonly asked questions about the effect of diet composition in the treatment of obesity. Effect of Diet Composition on the Amount, Rate, and Composition of Weight Loss Diet composition has no significant effect on the amount, rate, or composition of weight loss under conditions of a negative energy balance. The most significant factor determining the a

Evaluation of the Potential for Olestra To Affect the Availability of Dietary Phytochemicals

It has been hypothesized that phytochemicals found in fruits and vegetables are responsible for the inverse association observed between diets high in fruits and vegetables and risk of certain chronic diseases and cancer. This paper assesses the potential for olestra to affect the absorption of dietary phytochemicals and estimates the effect of olestra on the availability of carotenoids when olestra-containing snacks and foods containing carotenoids are eaten in free-living diets. Experimental data compiled on the effects of olestra on the availability of 29 compounds, mainly nutrients and oral medications, showed that olestra affects the availability of only molecules having octanol-water partition coefficients greater than approximately 7.5. Partition coefficients compiled for 382 dietary phytochemicals showed that only two classes of phytochemicals, phytosterols and carotenoids, contain molecules with octanol-water partition coefficients in the range in which olestra could potentially affect bioavailability. The potential effect on the bioavailability of phytosterols would be <10% and would not be expected to be of concern inasmuch as the hypothesized benefit of consuming pharmacological amounts of phytosterols is to reduce cholesterol availability, a function also of olestra. A 5.9% reduction in the average effective beta-carotene intake was calculated for individuals eating olestra-containing snack foods in free-living diets. The calculation was made by assuming that carotenoid bioavailability would be reduced to the extent measured in human clinical studies each time olestra-containing snacks and carotenoid-containing foods are eaten together and that all snacks eaten are made with olestra. Among individuals with low carotenoid intakes (the lowest 10%) the calculated reduction was 6.0%; for heavy snack eaters (the top 10%) it was 9.5%. These effects on carotenoid bioavailability are similar to those that can occur with other dietary factors.

The effects of water and non‐nutritive sweetened beverages on weight loss during a 12‐week weight loss treatment program

To compare the efficacy of non‐nutritive sweetened beverages (NNS) or water for weight loss during a 12‐week behavioral weight loss treatment program.