If you meditate on a regular basis and do not have a balanced diet, you are not going to acheive mental strength that will last a long period of time because eventually your body will be exhausted from what you're putting into it and the mind will be working over time to keep the focus and determination of positive thinking.
I'm not just promoting meditation and yoga, but an overal lifestyle of well being! It is our job to build on our awareness. Awareness truly is the first step and then secondly is choice. Continue to contribute to your mental strength by fueling your body with nourishing foods, creating a strong mind and body.
Don't hesitate to meditate, but hesitate the junk food!!