i-food (isotopic food) contains nutritients in which some atoms are substituted with their heavier non-radioactive isotopes. It has been suggested by Dr Mikhail Shchepinov as a way, so far hypothetical, to increase human longevity. Consumed with food, some biomolecules (e.g., essential aminoacids) become building material for the human cells. Those molecules that contain heavier isotopes are less prone to destructive effect of free radicals (the key point of the free-radical theory of ageing).

References:

Shchepinov, M.S. (2007) Reactive oxygen species, isotope effect, essential nutrients, and enhanced longevity. Rejuvenation Res. 10, 46-70

Demidov, V.V. (2007) Heavy isotopes to avert ageing? TRENDS in Biotechnology Vol.xxx No.x Pages.xxx-xxx (pre-published at the time of writing the article)