Research into calorie restriction - the diet choice that has been proven to extend healthy life span as well as confer many health benefits - has so far concluded that it works through changes to the Sir2 gene that increase expression of certain proteins (sirtuins such as SIRT1).

Earlier this week, one researcher group claimed that calorie restriction operates through a mechanism other than tweaking Sir2 - at least in yeast. Betterhumans has another article on this new discovery:

If caloric restriction truly extends lifespan by causing an overexpression of Sir2, then studies suggest that combining caloric restriction with Sir2 overexpression should have no additional effect on lifespan.

Kennedy and colleagues have found, however, that combining caloric restriction with Sir2 overexpression or Fob1 mutation actually increases yeast lifespan.

"Further," say the researchers, "calorie restriction results in a greater lifespan extension in cells lacking both Sir2 and Fob1 than in cells where Sir2 is present."

The findings suggest that a pathway besides Sir2 is responsible for the increased longevity, say the researchers.

Not everyone is sold, however:

"I disagree with the conclusions," says Leonard Guarente of the Massachusetts Institute of Technology in Cambridge, an expert in Sir2 and the molecular basis of aging. "They find a new, ill-defined pathway that can mediate caloric restriction in their strain. This in no way challenges earlier findings that in a different strain, a well-defined pathway including Sir2 does mediate caloric restriction."

Leonard Guarente is one of the founders of Elixir Pharmaceuticals, a company that is is currently licensing one of the new calorie restriction mimetic drugs as a complement to longer term healthy life extension research. As I've probably mentioned before, I like to see scientists arguing - it's usually a sign of progress.