The author indicates that caloric reduction extends the life of a mammalian cell by

The author indicates that caloric reduction extends the life of a mammalian cell by INITIATING A SERIES OF STEPS THAT RESULTS IN THE INCREASED PRODUCTION  OF CERTAIN ENZYMES.
Based on the passage, the author believes that when one eats less food, it stimulates the mammalian cells to produce certain enzymes which enable a cell to live longer. Increasing the life span of the cells ultimately result in increasing the life span of the animal involved. Thus, the author believes that one can live longer by eating less food.

The answer is b, as with an inference you make a statement with no evidence