Researchers in Denmark discovered that fasting impacts key chemicals in the brain differently for lean and obese subjects.
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About this Podcast:
In the first study of its kind, scientists in Amsterdam discovered how fasting changes brain levels of key appetite-controlling neurotransmitters serotonin and dopamine in lean individuals but not in obese subjects. Previous studies have demonstrated that the hypothalamus and thalamus regions of the brain are essential in regulating appetite and meal intake. Serotonin, in particular, appears to play a significant role in governing satiety by acting as an appetite suppressant. Lower levels of it are found in insulin-resistant obese subjects compared to lean controls, according to this same research group.
After a 24-hour fast, the scientists discovered via SPECT scans a significant increase in serotonin signaling in the hypothalamus in lean subjects but not in obese subjects. The researchers suspect that insulin resistance and metabolic inflexibility, commonly present in obese individuals, may have contributed to the lack of fasting-related increases in this key neurotransmitter.
They think this may be due to fasting-related changes in insulin and free fatty acids. Detailed analysis showed that changes in these hormones accounted for a significant amount (44%) of the increases in serotonin in the brain of lean subjects. It’s plausible that obese individuals were affected by reduced metabolic flexibility and thus a blunted fasting-induced reduction in insulin and a rise in free fatty acids.
Perhaps more consistent fasting paired with exercise and nutrition changes aimed at improving metabolic flexibility could improve fasting-related shifts in these neurotransmitters that regulate appetite and satiety.
Fasting is not the only thing that impacts appetite regulatory messengers. Prior study found when obese men consumed 50% of their daily calories at breakfast, dopamine and serotonin increased significantly; yet, when 50% of calories were consumed at dinner, they both decreased.
What can we take away from these findings? If you’re seeking to improve your body composition and/or struggle with food cravings, try eating more of your daily calories earlier in the day and consider adding exercise to your fasting regime as it may accelerate the improvements in brain chemicals governing appetite.
van Galen, K. A., Booij, J., Schrantee, A., Adriaanse, S. M., Unmehopa, U. A., Fliers, E., et al. (2021). The response to prolonged fasting in hypothalamic serotonin transporter availability is blunted in obesity. Metabolism: clinical and experimental, 154839. http://doi.org/10.1016/j.metabol.2021.154839
Versteeg, R. I., Schrantee, A., Adriaanse, S. M., Unmehopa, U. A., Booij, J., Reneman, L., Fliers, E., la Fleur, S. E., & Serlie, M. J. (2017). Timing of caloric intake during weight loss differentially affects striatal dopamine transporter and thalamic serotonin transporter binding. FASEB journal: official publication of the Federation of American Societies for Experimental Biology, 31(10), 4545–4554. https://doi.org/10.1096/fj.201601234R