There is such thing as overtraining and many people unfortunately find themselves with the “all or nothing” attitude towards exercise (and diet for that matter).
Disclaimer: Please keep in mind that I am not a Registered Dietitian. While my advice relies on my own personal experience and research, what has been successful for myself and others may be not best for you. You should always consult your doctor when making changes to your diet. If you have any questions or comments please feel free to email me at email@example.com.