Nutrition is key for performance and a fit life. CrossFit recommendation is to eat meats and vegetables, nuts and seeds, little fruit, low starch and NO sugar. Start your journey by eating whole clean foods and drinking plenty of water. Ditch the processed junk and get off the sugar. How do you know if it is a whole clean food, read the labels……well wait whole clean foods have no labels. If you can not pronounce the ingredients or there is a laundry list on the back of the package more than likely it is not a whole food. Shop the perimeter of the grocery isles and learn how to read a label.
The Zone diet is a good place to start getting you nutrition back in line. http://www.zonediet.com/
You can also learn more here https://library.crossfit.com/free/pdf/cfjissue21_May04.pdf
WHAT SHOULD I EAT BEFORE A WORKOUT: You want to get a good amount of protein, slow burning carbohydrates, and a little good quality fat.
WHAT SHOULD I EAT AFTER A WORKOUT: Here you want a 3:1 ratio of fast digesting carbohydrates to protein NO fats at this time.
SUPPLEMENTATION: A quality fish oil, magnesium malate, vitamin D 3-5000iu, multi-vitamin and a probiotic. Please check with your doctor before deciding to take any of these supplements.