How does the body physiologically adapt?

The body is extremely good at maintaining homeostasis (a stable internal environment). It is so good that it shuts down it’s least vital systems in times of stress to protect its survival. Stress can exhibit in the forms of overtraining, under eating and any detrimental ongoing psychological stress. This is why females who have lost their cycles are often underweight for their body type and genetics, and if you have skipped a month it could be due to stress.

When you are stressed your body elicits a fight or flight response via the sympathetic nervous system . This inhibits the digestive system regulating optimally and stimulates cardiovascular activity in order to bring oxygen to the working muscles in order to cope and overcome the stressors.

When you consume more energy than your body is used to burning your body is great at upregulating it’s digestive energy and working to meet the demands of the incoming energy. Calories in calories out is therefore a very blanket statement and diminishes the fact the body is smart at burning through the additional energy. Through the upregulation of NEAT (non-exercise activity thermogensis), digestive energy and upregulating all your bodies systems to have you feeling the best you can.