The lay press and the world of self-help magazines are filled with ruminations about the cognitive decline of the aging brains of baby boomers, the obesity of their grandchildren, and the obesity of the society generally. These topics are drawn together by the well documented finding that restricting calories leads to greater longevity. Indeed molecular biologists have been studying this phenomena for years in yeasts. C. elegans, and mice and have shown that a particular set of genes stand between food and aging. These are the SIR (silent information regulator) genes especially the SIR2 gene (SIR2a is the mammalian homologue). Over-expression of SIR2 results in a 30% increase in lifespan whereas depletion of SIR2 results in a 50% decline in lifespan where lifespan is measured in number of divisions.
After 40 years of age we all experience senior moments with forgetting of names, places, what other have told us, and where we have put things. Other cognitive changes occur as well though not as obviously. These are direct results of the physical changes our brains undergo. It is now known that down-regulating of gene expression increases with brain aging. Gene products that are inhibitory such as are mediated by gammaminobutyric acid (GABA) are especially vulnerable. The changes that are seen are not neuronal loss but rather loss of functional connectivity which results in less organized activity than was present in earlier years. These changes are thought to result in changes of executive function including impulse control and planning for the future.
Patients often ask whether these type of changes reversible. The answer is probably yes. A controlled and sensible decrease in the amount of calories consumed has been demonstrated to extend the lifespan of a variety of animals including mammals. It can also have effects on the brain. Indeed the down-regulating described above can be slowed and this in turn slows the neuronal degradation One study demonstrated an improvement in verbal memory of the cohort involved.
Finally, the SIR2 gene mentioned above fits into the story of caloric restriction. If you increase its expression, the yeast lives longer. If you restrict the caloric restriction of the yeast, you get the same result. If you look for the levels of SIR2 protein, you find that it is elevated in starvation. These findings are obtained in yeast, insects, and mammals.
If you would like to live longer, one thing that helps a lot is eating less.