Maintaining weight loss achieved through calorie restriction is difficult because of the biological adaptations elicited by the approach. Existing literature suggests diet macronutrient composition affects brain activity in regions controlling hunger and satiety. However, it is not clear if these changes are influencing weight loss maintenance. Holsen and colleagues addressed this question in a study they report in the August 2021 issue of The Journal of Nutrition.
Subjects involved in an existing randomized controlled feeding trial were recruited to participate in a study to explore regional cerebral blood flow (n=76). The subjects were provided diets containing high (60%), moderate (40%), or low (20%) levels of carbohydrate as a percentage of total energy. Cerebral blood flow was measured in regions involved in hunger and reward using functional magnetic resonance imaging before a meal and at 4 hours after the meal when subjects had been on the diet for 14-20 weeks.
Measures 4 hours after the meal indicated blood flow was higher in the nucleus accumbens for subjects consuming the high carbohydrate diet, relative to those consuming the low carbohydrate diet. In addition, blood flow in the hypothalamus was higher before the meal for subjects consuming the high carbohydrate diet. Because there were no differences in blood flow before or after the meal, the authors suggest the changes were more chronic, and not due to acute responses to a meal. The authors concluded that the elevation in cerebral blood flow in response to a high carbohydrate diet may affect the brain’s reward and homeostatic activity so as to impede weight-loss maintenance.
In a commentary, Hwang indicates results from this well controlled trial support the need for further work to determine if changes in postprandial glucose concentrations are meaningfully modulating brain activity. Hwang also points out the need to continue testing whether changes in the central nervous system have an impact on behavior and weight loss success.
Laura M Holsen, W Scott Hoge, Belinda S Lennerz, Hilâl Cerit, Taryn Hye, Priyanka Moondra, Jill M Goldstein, Cara B Ebbeling, David S Ludwig, Diets Varying in Carbohydrate Content Differentially Alter Brain Activity in Homeostatic and Reward Regions in Adults, The Journal of Nutrition, Volume 151, Issue 8, August 2021, Pages 2465–2476, https://doi.org/10.1093/jn/nxab090.
Janice J Hwang, Food for Thought, The Journal of Nutrition, Volume 151, Issue 8, August 2021, Pages 2089–2091, https://doi.org/10.1093/jn/nxab210.