The present day science of metabolism is far from simple and clear-cut, and especially so in fields making dramatic process. This NYT article on calorie restriction (CR) research is illustrative of this point; one has to be careful parsing out their claim of no proof for the health benefits of human CR, given there are studies that show these benefits - but there are no multi-thousand member, multi-decade studies, for example. You always have to ask what is meant by "prove" in popular science pieces. From the article: "A new class of drugs is looming on the horizon that could, if they live up to their promise, avert heart disease, diabetes, cancer and neurodegenerative disorders. By suppressing the common killers of age, the drugs, sirtuin activators, could significantly prolong both health and lifespan. But is the promise a mirage or a serious possibility?"

Link: http://www.nytimes.com/2006/11/07/science/07drug.html?pagewanted=print