For most athletes, the recommended time during the yearly training cycle to begin restriction of energy intake to lose large amounts of stored body fat is:

For most athletes, the period in their yearly training cycle during which it is recommended to begin calorie restriction so as to lose significant amounts of stored body fat is the off-season or early in the preseason. Restriction of energy intake late in the preseason when there is rigorous training or during season when there is competition may impede training, recovery, or performance.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.