Food restriction, like exercise, triggers a biological program that stimulates the restoration of energy balance following a decrease in the amount of energy stored. This response involves genetic and hormonal components that in turn drive food intake (i.e., hunger). Previous studies linked this biological response to a reduction of anxiety in both humans and rodents. The chemical changes that occur during food restriction have shown similar anxiolytic effects (i.e., reduce anxiety) as exercise does.
NEUROPEPTIDE Y & GHRELIN
The main players in the chemical reaction triggered by food restriction are endogenous proteins like neuropeptide Y (NPY) and ghrelin (i.e., ghrelin is released when you are hungry to stimulate food intake), and they are thought to mediate antidepressant and anxiolytic effects. For example the expression of NPY receptors in the amygdala (i.e., the protein needs receptors to be processed, and the more receptors the higher the quantity that is processed) was previously associated with a reduction of anxiety.
TESTING THE EFFECTS OF HUNGER ON PTSD SYMPTOMS
Extending these findings, the current study seeks to investigate whether NPY and ghrelin attenuate anxiety associated with post-traumatic stress disorder (PTSD). The authors put hungry rats under an inescapable foot shock procedure (IFS), which is an animal model for PTSD, and observed their behavior. Their results indicate that although the rats appeared less anxious, as they displayed increased locomotion and decreased freezing behaviors (i.e., when rats are anxious, they typically freeze in place and don’t explore the environment), food restriction did not sufficiently reduce the more pathological anxiety state of PTSD. This conclusion is supported by the observed decrease in the number of certain types of NPY receptors in the amygdala (i.e., a reduction in the number of receptors suggests that the protein cannot be effectively processed), suggesting decreased anxiolytic effects.
One possible interpretation for these results is that in general food restriction stimulates learning that promotes fear extinction (e.g., learning that being at the same location where a trauma took place does not mean danger), but with PTSD this learning process is inhibited, which in turn prevents a reduction of anxiety. Similarly, memory impairment could also explain the absence of anxiety reduction in those rats exhibiting PTSD-like symptoms.
Therefore, results do not support food restriction as a possible therapy for the treatment of PTSD.
Hendriksen H, Bink DI, Vergoossen DL, Suzet van Slobbe E, Olivier B, Oosting RS. Food restriction does not relieve PTSD-like anxiety. Eur J Pharmacol. 2015 Apr 15;753:177-82. doi: 10.1016/j.ejphar.2014.10.060. Epub 2014 Nov 22. PMID: 25460029.