Evidence dating back to the 1930s shows how lifespan can at least be extended, but there is no magic potion. McKay reduced the calorie intake in rodents by a third without compromising on essential nutrient levels to bump up their life expectancy by 40%. This is also true for yeast, roundworm, and fruit flies, though evidence in humans remains anecdotal. The US National Institute on Aging are working on this by investing in a long-term study called CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) to see whether there is a link between calorie restriction, disease and ageing.

Observation, however, is never enough for the scientist. A gene, a key regulator and a molecular pathway by which calorie restriction can slow down ageing are needed. Calorie restriction might slow down metabolism by reducing harmful free radical levels in the body, thereby prolonging life. But, some studies reveal that certain metabolic activities are more likely to increase on a low-calorie diet.

Baker’s yeast yielded a breakthrough. By simply counting the number of times a cell divides before dying, Guarente and colleagues at MIT in Boston discovered that a gene called Sir2 (for Silent Information Regulator) is linked with increasing lifespan. Indeed artificially upping Sir2 levels boosts lifespan just like the calorie restricted diet. And so began a journey in understanding how “tweaking a handful of genes,” as Guarente and Sinclair put it, can prolong life.