Associations of Brain Reactivity to Food Cues with Weight Loss, Protein Intake and Dietary Restraint during the PREVIEW Intervention.

The objective was to assess the effects of a weight loss and subsequent weight maintenance period comprising two diets differing in protein intake, on brain reward reactivity to visual food cues. Brain reward reactivity was assessed with functional magnetic resonance imaging in 27 overweight/obese individuals with impaired fasting glucose and/or impaired glucose tolerance (HOMA-IR: 3.7 ± 1.7; BMI: 31.8 ± 3.2 kg/m²; fasting glucose: 6.4 ± 0.6 mmol/L) before and after an 8-week low energy diet followed by a 2-year weight maintenance period, with either high protein (HP) or medium protein (MP) dietary guidelines. Brain reactivity and possible relationships with protein intake, anthropometrics, insulin resistance and eating behaviour were assessed. Brain reactivity, BMI, HOMA-IR and protein intake did not change differently between the groups during the intervention. In the whole group, protein intake during weight maintenance was negatively related to changes in high calorie images>low calorie images (H > L) brain activation in the superior/middle frontal gyrus and the inferior temporal gyrus (p < 0.005, corrected for multiple comparisons). H > L brain activation was positively associated with changes in body weight and body-fat percentage and inversely associated with changes in dietary restraint in multiple reward, gustatory and processing regions (p < 0.005, corrected for multiple comparisons). In conclusion, changes in food reward-related brain activation were inversely associated with protein intake and dietary restraint during weight maintenance after weight loss and positively associated with changes in body weight and body-fat percentage.

Satiety and memory enhancing effects of a high-protein meal depend on the source of protein.

OBJECTIVE: High- protein diets have become increasingly popular with various touted benefits. However, the extent to which protein quantity and source affects cognitive functioning through altering postprandial amino acid profiles has not been investigated. Further, whether all protein sources are similarly anorexigenic is uncertain. The objective of this study was to determine the influence of protein level and source on Barnes maze performance, satiety and plasma amino acid levels in male Sprague-Dawley rats. METHODS: Rats were entrained to a meal-feeding schedule consisting of a 30 minutes meal, equivalent to 20% of average daily intake, one hour into the dark phase then ad libitum access to food for 5 h. On test days, rats received one of three isocaloric diets as their first meal, hereafter referred to as Egg White (EW), Wheat Gluten (WG), or Basal, and then were measured for cognitive performance, feeding behavior, or plasma amino acid levels via jugular catheter. Percentage energy from protein was 35% for both EW and WG and 20% for Basal with equal amounts provided by EW and WG proteins. RESULTS: Rats provided EW performed similarly to Basal on the Barnes maze, whereas WG performed worse. EW increased satiety, whereas WG reduced satiety relative to Basal. Both EW and WG increased postprandial concentrations of large neutral and branched chain amino acids relative to Basal, but in EW, concentrations were slower to peak, and peaked to a higher level than WG. DISCUSSION: Results demonstrate the importance of protein source for cognition and satiety enhancing effects of a high-protein meal.

Benefit beliefs about protein supplements: A comparative study of users and non-users.

The consumption of protein supplements among leisure time exercisers is growing. The present study aims to identify factors that motivate protein supplement consumption by comparing users' and non-users' underlying benefit beliefs about protein supplement. The study is based on an online survey of 813 Swiss adults (376 users of protein supplements and 437 non-users). Participants answered questions related to their benefit beliefs regarding protein supplement, their protein supplements consumption frequency, their activity level (GPAQ), and their reasons for taking protein supplement. In women, the most commonly cited reasons were to increase muscles (57.3%) and to regulate their weight (48.6%); and in men to increase muscles (83.7%) and to promote regeneration (53.7%). Furthermore, a principal component analysis revealed four benefit belief factors: (a) restore nutrients/avoid weakness; (b) fitness promotion; (c) health/well-being; (d) muscle modulation/competitive performance. The analysis showed that both users and non-users predominantly perceive protein supplements consumption as a strategy to modulate muscle mass, while beliefs in a health and well-being promoting effect was more prevalent among users (M = 3.2, SD = 1.3) than non-users (M = 2.7, SD = 1.3) (p < 0.001). Moreover, health and wellbeing-related beliefs were associated with an increased likelihood of a higher protein supplements intake frequency (OR = 1.5, 95% CI: 1.1-1.9), while physical activity level was not associated with protein supplements intake frequency. In addition, a negative correlation between physical activity level and beliefs in a fitness-promoting effect of protein supplements (r = -0.14, p < 0.001) was observed, indicating that for a subgroup, protein supplements might license lower activity levels. Despite a lack of scientific evidence, consumers of varying activity levels consume protein supplements and believe in its' various positive features. Users should be better informed to prevent misguided health beliefs.