Location: Healthy Body Weight Research
Project Number: 3062-51000-057-001-T
Project Type: Trust Fund Cooperative Agreement
Start Date: Jun 15, 2016
End Date: Dec 31, 2020
Reducing energy intake below baseline increases the reinforcing (motivating) value or ‘wanting’ of food in general and may especially increase the ‘wanting’ of energy dense snack foods, particularly in overweight/obese women; thus contributing to the struggle of adhering to a weight control diet. While protein-rich diets are efficacious for achieving and maintaining a healthy body weight, little is known about whether consuming protein (particularly beef) in a more even distribution throughout the day reduces the motivation for snacking on energy dense foods and a woman’s ability to stay ‘on track’ with her weight control behaviors and goals. Our general hypothesis is that, in overweight/obese women, beef consumed as part of an even protein distribution intake pattern will: a) reduce loss of lean mass during weight loss; and b) increase adherence during healthy dieting by increasing dietary satisfaction, dampening the increase in the motivational drive for energy dense snack foods that occurs with energy deficit, increasing the satiating value of a meal, and delaying hunger. To test this hypothesis we will compare diets with two protein intake patterns with a 500 kcal/day deficit. Specific Objectives: The overall objective is to test the efficacy of two patterns of daily protein intake (32en% from beef) to promote healthy changes in body composition and dietary adherence during weight loss. We will do this by accomplishing the following specific aims: Specific Aim 1: Determine the effects of beef consumption as a component of two patterns of daily protein intake on changes in fat mass and fat-free mass during weight loss. Specific Aim 2: Determine the effects of beef consumption as a component of two patterns of daily protein intake on weight loss diet adherence and putative mediators (satisfaction, satiety, hunger, motivation to snack on energy dense foods) of adherence.
Experimental Approach: Healthy overweight/obese (BMI: 28 – 40 kg/m2) women of childbearing age will complete a randomized parallel feeding trial evaluating two patterns of daily protein intake (even distribution across all meals vs. a skewed distribution with most protein consumed at the evening meal) on adherence to a caloric restricted diet. Intervention: Eligible participants will be randomly assigned to receive one of two patterns of daily protein intake for an 8 week energy restricted (~500kcal/day) period in which all foods will be provided, followed by an ad libitum eating period in which they will be asked to maintain a similar dietary pattern when buying, choosing and consuming their own foods for the next 8 weeks. Outcome variables will be tested at baseline, 8 weeks, and 16 weeks. Dietary Intervention: Study diets will be designed on a 5-day menu rotation, formulated with commonly available food items, isoenergetic and isonitrogenous, provide 90g of protein/day, and will differ only in daily distribution pattern. The skewed distribution pattern will model typical protein intakes of Americans: 10 g (breakfast), 15 g (lunch) and 65 g (dinner). The even distribution pattern will provide the same amount (30g) of protein at each meal. Study diets will be based on the 2015 DGA, providing 32en% (based on 12.5 oz eq/wk for a 2,000 kcal diet level) of the protein requirement as beef. Dietary advice will be provided in small groups during the first 8 weeks and focus on reinforcing positive dietary changes and addressing barriers to adherence. Outcome Variables: Primary outcome variables are: body composition, anthropometrics, diet adherence, and monthly measures of putative mediators of adherence. The motivation task will measure the amount of work an individual engages in to gain access to the food of interest versus an alternative. Treatment moderators will be assessed at baseline using validated questionnaires. Secondary outcome variables include: lipid metabolism, fasting glucose and insulin levels, and skeletal muscle protein breakdown. Power and Statistical analysis: Power estimates are based on the effects of protein as part of an energy-restricted diet in women on changes in total lean mass. Assuming a between subject SD of 1.4 kg, 23 participants per group will provide 90% power to detect a difference in lean mass losses. Changes in body composition over time will be assessed using a General Linear Model. Between subject factor will be diet with time as the within factor. Baseline body composition, the relative reinforcing value of energy dense snack foods, cognitive restraint, uncontrolled eating, emotional eating and impulsivity will all be considered for potential covariates. The effects of the dietary interventions on diet adherence and mediators of adherence, lipid metabolism, fasting glucose and insulin levels, and skeletal muscle protein breakdown will also be assessed using General Linear Models. Mediation analyses will also be completed. Tukey contrasts will be used for post-hoc comparison of means. P values < 0.05 will be considered statistically significant. All analyses will be conducted using SAS software.