Healthy aging has often been linked with reduced appetite and lower energy intake, possibly resulting in loss of weight, undernutrition and related health consequences. There are several causes for the fall in caloric intake, and usually involve physiological and non-physiological processes.

In a recent study, Peters and colleagues, at the Swinburne University of Technology, Melbourne, VIC, Australia, evaluated the effect of glucose on brain function in healthy adults as well as age-related, physiological changes in brain responses associated with macronutrient intake.

This randomized, double-blind, balanced cross-over study allocated 16 younger (aged 21-30) and 16 older (aged 55-78) adults to receive a drink containing glucose and a taste-matched placebo after an overnight fast. Investigators assessed blood glucose and hunger at baseline and 20 min post drink intake. This was followed by resting state functional magnetic resonance imaging in all the participants.

Researchers further explored the frequency-dependent changes associated with glucose administration in slow-5 (0.01-0.027 Hz) and slow-4 (0.027-0.073 Hz) amplitude of low-frequency fluctuations (ALFF) and fractional ALFF (fALFF) of the blood oxygen level-dependent (BOLD) signal within the young healthy adults, and these were then extended to the older age group.

Glucose diminished the amplitude in slow-5 fALFF within the left orbitofrontal cortex and insular cortex in the young adults. There was evidence of a significant interaction in slow-5 ALFF and fALFF in the left insula, in a way that the younger participants exhibited a reduction in BOLD amplitude, while the older ones demonstrated an increase, following glucose administration. Additionally, there appeared to be an interaction in slow-4 ALFF in the occipital region and precuneus; older participants had an increase in magnitude of slow-4 ALFF while the younger participants exhibited a reduction.

These age-related, frequency-dependent changes in the magnitude of the BOLD signal in the insula, a region pivotal for energy homeostasis following feeding, may signal a change in satiety or homeostatic signaling, thus having a role in behavioral changes in energy intake during old age.

Source: Peters R, White DJ, Scholey A. Resting state fMRI reveals differential effects of glucose administration on central appetite signalling in young and old adults. J Psychopharmacol. 2020 Mar;34(3):304-314.