A large and especially prolonged calorie deficit generally creates less favorable conditions for tissue recovery. Healing is an energy-intensive process: it requires energy (ATP, which the body gets from carbohydrates, proteins, and fats) and substrates for protein and collagen synthesis, fibroblast activity, immune response, angiogenesis (formation of new blood vessels to the tissues), and tissue remodeling (to arrange collagen fibers into the proper structures). When there is a significant lack of energy, the body starts conserving resources on these processes, and healing becomes worse.
To simplify the whole model, I’ll explain it this way:
Lack of protein and ATP
When there is an overall energy deficit, the AMPK signaling pathway is activated, which tells the body to conserve resources and not build new proteins, especially muscle proteins or connective tissue proteins, because they are not critical at that moment. During such a period, the body needs resources for the brain, breathing, and other essential functions. Roughly speaking, if you find yourself in a desert without food, the body understands that now isn’t the best time to heal injuries and doesn’t spend resources on it.
Enough resources
But when there is enough protein and energy (ATP), another signaling pathway, mTORC1, becomes active. Then the body understands that there are enough resources and they can be used to synthesize new muscle and structural proteins for tendons and so on.
That’s why modern reviews on tendon and ligament rehabilitation recommend avoiding significant energy restriction.
