Restricting calories without also exercising does not prolong lives

Virtually all studies on the subject show that reducing calories
can prolong the lives of yeast, insects and animals. However
a recent study shows that restricting calories in fruit flies and
preventing them from exercising does not prolong their lives (Cell
Metabolism, July 3, 2012). That means that restricting calories so
much that you don't have enough energy to exercise may not prolong
your life.

WHY CALORIE RESTRICTION WITHOUT EXERCISE DOES NOT PROLONG LIFE:
Calorie restriction causes flies to exercise more, and their
muscles to make and use more fat for energy, both of which
prolong their lives. Flies who were on a restricted diet and were
prevented from exercising did not live longer.

Muscles use primarily fat and sugar for energy. The increased
physical activity in calorie-deprived flies was caused by
increased fat production and usage by the flies' muscles.
Blocking fat synthesis specifically in the muscle tissue
prevented calorie restriction from prolonging life. To prolong
life, you need your muscles to make more fat and use it to power
your muscles. These are the same changes in muscles that occur
when a person starts endurance training.

CONCLUSION: Endurance training prolongs lives. Calorie
restriction, like endurance training, prolongs lives by causing
muscles to make a greater percentage of fat and to use more fat
during exercise. Flies who are on calorie restriction and are
prevented from exercising do not live longer. Dr. Kapahi, the
author, states that "Our work argues that simply restricting
nutrients without physical activity may not be beneficial in
humans."