The discovery of the effects of a Calorie Restriction diet (CR Diet) in the early twentieth century is the first time the human race learned how to significantly and consistently extend the maximum lifespan of a species.
After all the tens of thousands of years that humans dreamed about how to slow down aging, a way of doing so in another species was found. This ranks as one of the major biological discoveries of the twentieth century, on a par with such breakthroughs as discovering the helical structure of DNA, the Hayflick limit on cell division, cloning, and the polymerase chain reaction.
There are many ways to improve health, including exercise, cessation of smoking, eating more nutritious foods, vaccination, etc. These can lead to a healthier life for individual members so they live longer and hence can improve the average lifespan of a species. But none of these health measures will affect the maximum lifespan of a species.
CR does lengthen the maximum lifespan. It is the only known intervention found to do so. (Actually, recent advances based on CR research have led to discoveries in lengthening yeast life span through genetic changes). Later it was shown to do so in species other than the rats of the original experiments, although it has not yet been shown to do so in humans.
Model For Aging Research
The true significance of the CR breakthrough could not start to be realized until the latter part of the 20th century, when advances in the human understanding of molecular biology and medical sciences allowed scientists to begin addressing how CR worked. What specifically changes in an animal on CR that extends its lifespan so it outlives by a significant margin (up to 40%) all of its twins on a standard diet?
CR provides an experimental model that allows scientists to begin unraveling how aging occurs. Because of CR, it is possible to run experiments that compare the biology of otherwise identical animals, some on CR and some not. It is possible to look at how physiological systems, molecular pathways and gene expression change under the influence of CR and how that slows down aging.
CR in fact provides a scientific model to investigate the most fundamental questions about aging: Is aging inevitable? Is aging a preventable disease or a natural consequence of life? Is immortality possible?
Health Benefit Bonus
As a bonus, it also turns out that CR makes animals - and humans - healthier. Unlike measuring maximum lifespan changes, measuring health benefits can be done in both short lived and long lived species. People on CR get healthier. It happens quickly, within weeks and months. One company, Sirtris, was founded in 2004 to develop ways to mimic CR health benefits in humans by the use of drugs. Its research breakthroughs were so impressive that four years later the pharmaceutical company GlaxoSmithKline acquired Sirtris for $720 million in 2008.