If you notice where each named circle, EXERCISE, NUTRITION and REST, interloop, there are areas within them where only two circles are interlooping. Where Exercise and Nutrition interloops for example, weight gain will most likely be your result.
Where Nutrition and Rest interloop, fat gain will most likely be your result.
Where Exercise and Rest interloop, Weight loss will most likely be your result.
So consider this;
EXERCISE is the constructive phase of Fitness. It is how physical work is done to rebuild and renovate in order to enhance the appearance and functionality of the body.
NUTRITION supplys the necessary materials the Systems need to convert into the energy needed to Exercise, and the Building Blocks the body needs to repair and rebuild during the renovation of Exercising.
REST is when the body reassemble the digested Nutrition to formulate suitable recipes from the materials Exercise needs for Renovation, so repairing, rebuilding and rejuvenation can take place during Recovery.
Even though many may lean towards Exercise more than Nutrition, or vice versa, no one part is more important than any other. Being able to balance all three areas to equally complement each system will result in an organized routine that will manifest into FITNESS as shown in the middle where all circles interloop.