There isn't any convincing evidence showing fat loss causes metabolic damage; however, observations are more indicative of reversible adaptive thermogenesis.
The activities you do outside of the gym - cleaning your home and walking - can have a positive impact on your health. Conversely, choosing to watch TV instead can lead to metabolic syndrome.
60 minutes of daily exercise can improve your insulin resistance by 25%. 120 minutes of exercise can improve it by 50%. If you're looking to avoid metabolic diseases, get up and start moving.