Impacts of Wild Blueberries on Appetite and Weight Regulation
Impacts of Wild Blueberries on Appetite and Weight Regulation
The objective is to complete a two-phase study to assess how wild blueberries impact regulation of appetite of overweight and obese men and women as well as to determine if wild blueberries can promote more effective weight loss than an isocaloric control. For phase I, the acute effects of consuming 1-cup of frozen wild blueberries mixed into ¾ C of low-fat yogurt will be compared to consuming an isocaloric serving of yogurt mixed with an artificially flavored and colored blueberry syrup. During acute testing, subjective ratings of appetite, glucose metabolism, and appetite-regulating hormones will be assessed. Phase II will consist of an 8-week feeding trial in which the same subjects will consume daily servings of yogurt mixed with either frozen wild blueberries or placebo syrup along with intensive counseling for weight loss. The hypothesis is that wild blueberries will reduce hunger by regulating appetite hormones and promoting beneficial glycemic and insulinemic responses and that daily consumption of wild blueberries will translate to improved adherence to a weight loss regimen and therefore greater weight and fat loss. Secondary aims for Phase II of this project will include exploring the impacts of blueberry consumption during weight loss on antioxidant status, inflammatory markers, blood lipid profiles, glucose status, dietary intake, physical activity and blood pressure.
For Phase I, all subjects will complete two acute feeding trials in random order. One feeding will consist of 1 C frozen wild blueberries along with ¾ C low-fat Mountain High yogurt (total energy intake=170 kcal). The other feeding will consist of an isocaloric feeding of ¾ C yogurt mixed with artificially flavored and colored blueberry syrup (Torani). A standardized meal will be consumed the evening prior to testing to minimize fluctuations during the testing days. Arterialized fingerprick blood samples from heated hands will be collected into Greiner Bio-One MiniCollect™ Capillary Blood Collection System Tubes containing Ethylenediaminetetraacetic acid while fasted and 30, 60 and 120 minutes after food intake for analysis of glucose, insulin, ghrelin, and pancreatic peptide. Appetitive responses (hunger, fullness, desire to eat, and prospective food consumption) will be assessed by 100-mm visual analog scales at baseline and 15, 30, 45, 60, 90, and 120 minutes after intake.
For Phase II, subjects will be equally divided and matched for body fatness into two randomly assigned groups. Both groups will be counseled for weight loss, which will be achieved through a comprehensive program including a) dietary intervention, b) daily text messaging, and c) daily at-home weighing with a WiFi-enabled scale. In addition, groups will be randomly assigned to daily consume the same 170 kcal yogurt parfait described above containing either wild blueberries or placebo as an afternoon snack for 8 weeks. The rationale for the inclusion of a healthy, wild blueberry in yogurt afternoon snack intervention is supported by the National Health And Nutrition Examination Survey analyses that revealed a shift in eating patterns towards the evening in combination with an increase in snacking occasions, particularly in the afternoon/evening hours. Further, the majority of the snacking occasions include unhealthy, high fat/high sugar foods, potentially contributing to unwanted weight gain and obesity. Moreover, since blueberries can elevate pancreatic peptide for at least 2 hours after consumption, this could enhance the likelihood of maintaining lower intake during the evening meal. Thus, overall, it is proposed that the afternoon wild blueberry/yogurt snack will promote satiety and reduce overeating (especially of unhealthy foods) later in the day.
All participants will be counseled to achieve a 500-kcal/d energy deficit (from their baseline eucaloric diet). Energy requirements will be estimated by calculating resting metabolic rate using the equations of Schofield and multiplying by an activity factor of 1.3. The participants will meet with investigators every two-weeks for intensive counseling to ensure adherence to the dietary prescription. Before and after the trial, fasted blood will be collected into tubes for both plasma and serum to assess total antioxidant capacity, C-reactive protein, blood lipid concentrations, glucose and insulin. During lab visits investigators will assess anthropometrics (height, body weight, and body composition via dual x-ray absorptiometry, dietary intake, physical activity behaviors, food cravings, and blood pressure. Adequate samples of blood will be collected to allow us to bank plasma for future analyses if additional funding is obtained in the future.
Inclusion Criteria:
Exclusion Criteria: