A. V. Everitt, S. I. S. Rattan, D. G. Le Couteur, R. de Cabo (eds): Calorie restriction, aging and longevity
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- Cite this article as:
- Le Bourg, É. Biogerontology (2010) 11: 731. doi:10.1007/s10522-010-9290-7
The book Calorie restriction, aging and longevity edited by Everitt, Rattan, Le Couteur, and de Cabo has been written in a time of transition between the epoch when nearly every biogerontologist was convinced that caloric restriction (CR, also called dietary restriction, DR, by other authors) increases longevity and the current time, when a growing number of experts think that the longevity variations have to be linked with the composition of the diet rather than with calories per se. The sentence of Brian Morris introducing his chapter: “It is well established that caloric restriction (CR) extends lifespan of all species tested” illustrates the opinion of many experts and the reader could be thus disappointed when reading the chapter by Simpson and Raubenheimer, who clearly show that calories have no effect on longevity of various species, but rather that it is dependent on the ratio between carbohydrates and proteins, i.e., CR does not increase longevity.
The first part of the book, which describes the effects of CR in various species (humans, monkeys, flies, yeast, etc.) in seven chapters, is suffering from a major problem, according to me: some authors are so convinced by the validity of CR/DR to extend lifespan that they overlook contradictory results. For instance, the chapter on monkeys by Messaoudi et al. concludes that it has been reported “a lower incidence of age-related deaths in monkeys after more than 20 years of study”, but ignores other longevity results and criticisms of other authors (review in Le Bourg 2010). Similarly, that on Drosophila melanogaster written by Poirier et al. ignores authors who have reported absence of longevity increases and concludes that “extending Drosophila life span via DR has been firmly established”, without also considering that studies on other fly species could not report longevity increases. The chapter on human beings by Everitt et al. curiously gives credence to the idea that the 102-years longevity of Luigi Cornaro could be linked to DR, while his birthdate seems to be unknown (various sources report dates varying between 1457 AD and 1484 AD). This chapter is in fact more concerned with the effects of diet, lifestyle, body-mass index, and so on, on longevity than with that of CR itself, as no results showing that CR could increase longevity in human beings have been published (see the debate in Biogerontology, 2006, vol. 7, issue 3).
The second part of the book is entitled “Biochemical and metabolic mechanisms of calorie restriction” and contains six chapters. In their chapter on oxidative stress, Merry and Ash conclude that there is a “limited support only that oxidative stress and damage is important in controlling the rate of aging and is the mechanism through which DR feeding acts to increase longevity”, while this idea of a link between DR and free radicals was often considered in a recent past as suffering no doubt. Similarly, the role of pituitary hormones in CR effects is not very clear, as emphasized by Everitt et al. in their chapter on hormones: “interpretation of these findings is challenging”. Is hormesis the key to explain CR effects, CR inducing a mild stress disturbing homeostasis? Rattan and Demirovic consider that “it is the immediate responses to CR which best qualify to be considered as hormetic”, which leaves with no explanation the long-term CR effects. Therefore, it can be concluded that, more than 70 years after the first CR studies, the debate on the causes of its effects is not exhausted.
The third part of the book is concerned with clinical applications of CR. Chapters studying the impact of CR on cancer, obesity, cardiovascular disease, and physiological parameters in human beings predictive of such diseases convincingly show that CR, even when used for a limited time, can have positive effects, particularly in overweight and obese people.
After the reading of this book, I had the feeling that time is ripe for a paradigm shift: focusing the efforts not on lifespan but on healthspan. As a matter of fact, CR effects on longevity are less clear than previously thought and chapters on D. melanogaster by Poirier et al., on monkeys by Messaoudi et al., and on learning by Spangler et al. deliver a mixed message regarding the effects of CR on the aging process: CR can attenuate age-related problems but many studies also show that it can fail to do so, even when longevity increases have been reported. By contrast, it is very clear that implementing a mild DR in overweight and obese people is a source of not remote health benefits. Therefore, it seems more probable that CR could improve healthspan rather than to increase life span and delay aging. Could it be that CR mimetics, such as resveratrol, could be then of some use, as proposed by Brian Morris in his chapter? It could be, even if one can feel that the best move is to give up the unhealthy “SuperSize me” way of life. After all, if studies on CR on aging and longevity would have the unexpected consequence that they finally promote a better feeding behavior in people suffering from overweight and obesity, this would probably minimize the risk for a decreased life expectancy in the next decades (Olshansky et al. 2005). Colleagues working on CR could then conclude that their work was useful to people, even if not in the expected way.
In conclusion, this collective book is a useful one but the main conclusion after closing it is that CR is probably more useful to improve heathspan in adult life than to increase human longevity and delay aging. Indeed, this is not a problem.