On Hunger Without Calorie Restriction

It is suspected that some fraction of the benefits of calorie restriction for health and longevity are keyed to the hunger response in some way - i.e. that being hungry more often is necessary to gain the full effects. There's not all that much work on this so far as I'm aware, however. You might look at one study suggesting increased levels of ghrelin, the hunger hormone, are linked to an improved immune system response, for example. Studies investigating the contribution of hunger to the benefits of calorie restriction would have to run by manipulating the hunger response separately from calorie intake to try to isolate its effects.

Here is one recently published example of such a study. It is unfortunately focused only on aspects of Alzheimer's disease rather than on longevity, but it is still intriguing. The reduced inflammation is a sign that the researchers might be on the right track:

It has been shown that caloric restriction (CR) delays aging and possibly delays the development of Alzheimer's disease (AD). We conjecture that the mechanism may involve interoceptive cues, rather than reduced energy intake per se. We determined that hunger alone, induced by a ghrelin agonist, reduces AD pathology and improves cognition in [a] mouse model of AD.

Long-term treatment with a ghrelin agonist was sufficient to improve the performance in the water maze. The treatment also reduced levels of amyloid beta (Aβ) and inflammation (microglial activation) at 6 months of age compared to the control group, similar to the effect of CR. Thus, a hunger-inducing drug attenuates AD pathology, in the absence of CR, and the neuroendocrine aspects of hunger also prevent age-related cognitive decline.

Link: http://dx.doi.org/10.1371/journal.pone.0060437

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