Changing the level of effort you exert during an activity is an example of adjusting which training principle

physical health, mental health, emotional health, social health, and spiritual health

starvation is bad because your body needs nutrition and to deprive it of nutrition can cause problems with both health and fitness.

explanation:

it can make weight loss slow down over time, but it won't cause someone to gain weight depsite restricting calories. starvation causes weakness in the senses like thirst.