Project : USDA ARS

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Research Project: Dietary Guidelines Adherence and Healthy Body Weight Maintenance

Location: Healthy Body Weight Research

2019 Annual Report

Objectives
Objective 1: Identify psychological and physiological processes and factors that influence the motivation to exercise and to eat. Objective 1A. Determine whether incentive sensitization for physical activity is dependent on the dose and the pattern/intensity of physical activity. Objective 1B. Determine whether the level of negative energy balance influences the magnitude of alterations in food reinforcement. Objective 2: Determine whether the relative reinforcing value of vegetables or fruits can be increased through repeated exposure. Objective 3: Determine the effect of meal macronutrient composition on energy metabolism and substrate utilization and satiety. Objective 3A: Compare the effects of high- vs. low-protein breakfasts as components of two patterns of daily protein intake (even distribution of protein across all meals vs. a skewed distribution with most protein consumed at the evening meal) on energy metabolism, substrate oxidation, satiety and the reinforcing value of high-sugar, after-meal snack foods. Objective 3B: Determine the effects of consuming a sugar-sweetened beverage as part of low- (55% CHO, 15% PRO, 30% FAT) or high-protein (40% CHO, 30% PRO, 30% FAT) meals on energy metabolism and substrate oxidation, and satiety and RRV of high-sugar, after-meal snacks.

Approach
Achieving and maintaining healthy body weight underlies many critical aspects of health. The immediate choices people make about their foods and physical activities have cumulative effects that affect body weight and, ultimately, health. Yet, the motivational bases of those choices remain poorly understood; as are ways those choices may be moved towards healthier alternatives. This knowledge is needed for the development of new and effective tools to promote behavioral choices that support healthy body weight. This project addresses these needs by investigating how to increase the reinforcing value of physical activity, and ways to increase the reinforcing value of vegetables and fruits. It also will evaluate the motivating potential of providing real-time feedback on subject energy balance based on an analysis of breath. This project will yield empirical evidence that will inform dietary and physical activity guidelines and programs, and tools that can be used by workers in the health and fitness industries to help individuals make healthy choices regarding physical activity, diet, and maintenance of a healthy body weight.

Progress Report
Progress was made on all three objectives which fall under NP107. Objective 1 included completion of five clinical trials and one large cross-sectional study. Four of these studies focused on developing an exercise program that would simultaneously increase people’s fitness as well as their desire to exercise so that they could maintain an active and healthy lifestyle. The work aimed to understand and increase the motivating nature of exercise (exercise reinforcement), which would result in shifting the daily choice of being physically active or sedentary towards physical activity. This work started with a cross-sectional study that demonstrated for the first time that the motivating aspects of exercise and tolerance for the discomfort felt during exercise predicted who engages in enough physical activity to meet guidelines, and that the liking of exercise did not predict usual exercise participation. Through this work we also identified genetic differences. Tolerance for exercise discomfort, which predicts exercise reinforcement, is associated with genetic polymorphisms that moderate central reward processes, pain, and physical activity. With this knowledge, the next study sought to increase the motivating value of exercise by asking adults to exercise. All subjects in this first clinical trial trained for 6 weeks to determine whether repeated exposures to exercise increased their motivation to exercise. Exercise training reduced the motivation to be sedentary but did not increase the motivating value of exercise. Still, this is an important finding as it should help shift choice away from sedentary behavior and towards physical activity. A second clinical trial tested whether a greater ‘dose’ of exercise would help to increase exercise motivation. Similar to the first trial, participating in exercise sessions for 12 weeks decreased the motivation to be sedentary, but also increased exercise motivation. Notably, in both clinical trials, we found that the subsets of adults that did increase their exercise motivation also increased their tolerance for the discomfort of exercise and exercised at a greater intensity during their workouts. Armed with this evidence, we are finishing a third clinical trial where adults engage in high-intensity exercise that produces discomfort to empirically test whether exposures to discomfort increases tolerance for exercise discomfort and the motivation to exercise. Concurrent to our studies of adults we extended these ideas to children by studying whether playing active videogames increases the motivating value of active play. Encouragingly, in this fourth clinical trial, active videogame play increased children’s motivation towards traditional active play and did not increase motivation towards sedentary videogames. In ancillary work we completed a study to understand why some individuals lose more weight with exercise training than others. This study determined whether there are physiological and behavioral mechanisms that explain why some people compensate to the energy expended during exercise by eating more or being less active throughout the day resulting in no or little weight change. In a second ancillary study (a fifth clinical trial) we demonstrated that eating a low-sugar diet for 1 week increases the desire for foods high in added sugars. This work connects to the new project by extending our research to understand how signaling molecules released for muscle and fat in response to diets and exercise promote changes in exercise motivation. Objective 2A consisted of a large, randomized, controlled clinical trial with the goal to ascertain if incentive sensitization (repeated exposure) to vegetables could increase the reward value (reinforcing value) of vegetables. One-hundred two participants completed the 16-week protocol. The experimental diet consisted of providing vegetables, in the amounts and types recommended by the Dietary Guidelines for Americans (DGA), in minimally-processed form to overweight and obese individuals. We found that incentive sensitization, or repeated exposure, to vegetables in the amounts recommended by the DGA did not result in increased motivation to eat vegetables. This has implications for nutrition researchers, public health workers, and dietitians/nutritionists who work with U.S. consumers to improve diet quality by including vegetables into the diet. A secondary outcome, substitution, was also evaluated in this study. As the DGA recommends ~300kcal/day from vegetable intake, we investigated whether people substituted the provided vegetables for other, higher-calorie foods, or simply added the vegetables to their usual diet. We found that participants did substitute vegetables for snacks and protein foods, but also for whole fruits. These results highlight the public health importance of emphasizing the substitution of vegetables for other, more energy-dense foods. The study design for Objective 2B has been amended to include secondary endpoints that are very pertinent to individual’s ability to reduce and maintain recommended amounts of added sugars in their diet. The primary outcome of the objective remains the same; to investigate the reinforcing value of fruits by incentive sensitization but now includes hypotheses relating to a person’s ability to taste low amounts of sugary foods, and what level of sweetness they prefer. To investigate these aims, we are 1) giving people DGA amounts of fruit, 2) a complete diet including natural sugars (such as those found in fruits) but no added sugar, and 3) an attention control group. This work connects directly with the new Project Plan which examines the DGA’s influence on physiological and psychological outcomes. Objective 3 aimed to understand how changes in the macronutrient composition of a meal, specifically dietary protein and added sugars, and intake patterns alter energy metabolism, substrate oxidation, and food reinforcement. In the first clinical trial we found that drinking a sugar-sweetened beverage with a meal reduces energy efficacy and fat oxidation. Furthermore, these alterations in energy metabolism were exacerbated when the sugar-sweetened drink was paired with a protein-rich meal. One implication of these results is that the body’s reduced metabolic efficiency after drinking a sugar-sweetened drink can lead to a greater tendency to make and store fat. Additionally, we found that changes in the macronutrient composition of a meal does not influence the reinforcing value of sweet tasting, energy-dense foods when consumed as a snack outside of the meal time. These results demonstrated that the highly reinforcing properties of sugar are difficult to overcome. However, we did find that when women eat a protein-rich meal their wanting of energy-dense savory snack foods (e.g., potato chips) is significantly less than after eating a lower protein meal; there was no difference in men. One implication of this research finding is that increasing the amount of protein consumed at a meal can influence a woman’s snacking behavior. In a second clinical trial we demonstrated, for the first time, that increasing the amount of sugar in a food produces a measurable psychoactive dose response. Using a questionnaire developed to assess the subjective effects of psychoactive drugs we found that increases in the sugar content of chocolates increases the number of positive responses on the questionnaire. These results suggest that the reward centers in the brain are sensitive to the amount of sugar in a food and help explain why it is so difficult to decrease sugar consumption. We are currently finishing two other clinical trials to determine how the distribution of dietary protein impacts energy metabolism, substrate oxidation, food reinforcement, and ultimately weight control. In these clinical trials we are testing the effects of evenly distributing protein intake throughout the day compared to typical consumption patterns in which the majority of protein is consumed at the evening meal. In one of these two clinical trials we are testing the acute effects of protein distribution patterns on energy metabolism, substrate oxidation, and the reinforcing value of energy-dense and nutrient-dense foods. To date 20 of 40 subjects have completed all testing in this randomized cross-over study. This study will help us begin to understand the connection between the foods we eat, energy metabolism, and motivational outcomes related to increased energy intake due to snacking. In the other clinical trial, we are testing the effects of protein distribution patterns on a woman’s ability to stay “on track” with her weight control behaviors and goals. This study will help begin to elucidate the connections between the daily pattern of protein intake on body composition during weight loss, adherence to a weight control diet and alterations in the reinforcing value of energy-dense snack foods. To date 26 of 43 subjects have completed all testing in this randomized parallel study design. We are extending these ideas in our new project plan by testing how dietary intake patterns affect metabolic flexibility and alter dopamine modulation in the brain, which is responsible for reward seeking behavior.

Accomplishments
1. Why it can be so difficult to stop eating sugary foods. Eating a low-sugar diet for one week increases the desire for foods high in added sugars. The Dietary Guidelines for Americans (DGA) have recommended reducing added sugar intake since its inception in 1980. Nearly 40 years later, added sugar consumption still exceeds recommendations among most of the population. One problem is that added sugars are highly reinforcing, so people really want to eat them. ARS researchers in Grand Forks, North Dakota, demonstrated for the first time that restricting intake of foods high in added sugars made them more reinforcing. People wanted to eat them even more, making it difficult to maintain reductions in the foods with added sugars, which are energy-dense and excessive consumption is linked with increased risk of obesity. Thus, abrupt reductions in intake of reinforcing foods to meet the Dietary Guidelines for Americans are not likely to result in habit change. Guidelines for dietary behavior change may want to promote gradual changes.

2. Vegetable variety or amount - determining which is most effective at lowering chronic disease risk. ARS researchers in Grand Forks, North Dakota, demonstrated using a large, nationally representative sample of Americans that both the amounts and the variety of vegetables Americans eat is associated with a lower prevalence of coronary heart disease, and that the amount of vegetables people eat is associated with lower risk of death from chronic diseases. This finding is important in that the Dietary Guidelines for Americans recommends that people increase both the amount and variety of vegetables consumed. This research shows that if we can just get people to increase the amounts of vegetables they consume, there are still health benefits, but increasing both is best. This is important as vegetables are nutrient dense, mostly low-energy foods that, if used to replace higher calorie foods, can contribute to maintenance of a healthy body weight.

3. Eating eggs for dinner can lower food costs. A recognized approach to improve diet quality is to incrementally replace commonly consumed foods with targeted healthy foods, which is known as the “small changes” approach. Eggs are a good candidate for this approach because they are nutrient-dense, easy to prepare, and are part of a wide range of cultural food menus. However, the cost of healthy foods, like eggs, may present a barrier to improving diet quality. ARS researchers in Grand Forks, North Dakota, demonstrated that if people ate eggs instead of other commonly-consumed meal items, food costs can be reduced by up to $1.99 per person per day, representing over 20% of food expenditure. Replacing other commonly consumed foods with eggs at some eating occasions may be a simple and practical way to improve diet quality and reduce calorie intake while simultaneously reducing daily diet costs.

4. Eat the amount of vegetables recommended by the Dietary Guideline for Americans. Identified key facilitators and barriers to consuming the Dietary Guidelines for Americans recommended amount of vegetables in individuals who typically consume less than one vegetable serving per day and those who consumed the recommended amounts during an 8-week intervention. ARS researchers in Grand Forks, North Dakota, found that the barriers and facilitators identified by these groups differed in relative rankings, suggesting that the experience of consuming provided vegetables influenced the strength of the perceived barriers and facilitators. Knowledge emerged as both a core barrier and facilitator in this sample of adults and is likely a factor for adults in other parts of the country. Specifically, knowing where to find vegetable intake recommendations and how to implement the recommendations were common themes. Perceived higher cost of fresh vegetables remains an intractable barrier, as well as the perceived time constraint in preparing them. The multi-factorial nature of the identified barriers and facilitators underscores the importance of addressing both individual and environmental factors in designing successful programs to increase vegetable consumption to amounts that confer health benefits. These findings extend our understanding of determinants of food choice behavior, offering new insights focused specifically on vegetable consumption. This is important as vegetables are nutrient dense, mostly low-energy foods that, if used to replace higher calorie foods, can contribute to maintenance of a healthy body weight.

5. Snacking maybe hindering our weight control success. Snacking accounts for about 24% of our daily caloric intake and snacking in the absence of hunger is associated with greater body weight. ARS researchers in Grand Forks, North Dakota, demonstrated that dietary restriction aimed at eliminating between-meal snacking increases cognitive restraint of eating and decreases disinhibition and that the conscious intention of adhering to eating only 3 meals/day may improve the perception of hunger cues while reducing susceptibility to external food cues, helping people to maintain a healthy body weight.

U.S. DEPARTMENT OF AGRICULTURE

Healthy Body Weight Research: Grand Forks, ND