I keep forgetting there's a time limit to edit. This is the part of the Dr. Denito authored article I linked above that has to do directly with food and nutrition. I'm only pasting this because the article is very long and includes stuff about injury, stress, recuperation, and all that as well. Again, it's meant to be generally educational. For individual needs a personal doctor is best.
The dedicated gymnast often doesn't have a diet with many bad foods in it, but rather a diet with too limited an amount of good foods. The greatest area of deficiency is in the fats/oils, followed by the proteins. This is likely under the premise that the dietary fats will make them fat. The fats they need more of are not man-made margarines, fried foods or beef and chicken in nature. They need more fish, eggs, nuts and seeds. These sources of fats/oils are critical at controlling inflammation and balancing their ever challenged steroid hormones, as well as promoting bone and muscle regeneration. They are the main sources to help the body maintain levels of Vitamin A, D and K. Fish should be consumed 2 times a week, and a fistful of nuts and seeds consumed daily. The better nuts include almonds, macadamias, pine nuts and walnuts. The better seeds include pumpkin, sesame, sunflower or flax. These foods are also good sources of protein. Eggs (free of hormones/ antibiotics) should also be eaten (if no sensitivities) about 4-6 per week. You can always use a protein shake made from a mixture of rice and whey protein to stabilize mid-day blood sugars or blended with fruit as an easy breakfast.
What about fruit? Eat at least 2 fruits per day. Use no fruit juices, unless diluted with water 4 to 1. Dried fruits are also excellent to consume during meets. Girls especially will benefit from dates and figs. Sugars to use are xylitol, mannose, ribose or honey (unfiltered cloudy quality). Stay away from using only commercial sports drinks. Make your own by using the diluted fruit juices of either Noni, Acai, Pomegranate, Goji, or Blueberry, with a splash of lemon juice and a tiny pinch of sea salt added.
Vegetables should emphasize the dark green and bright orange colors. The cruciferous vegetables (cabbages, broccoli, brussel sprouts, and cauliflower) are excellent sources of sulfur needed by the connective tissue, as well as the liver to maintain hormone balance. The cruciferous group generally digests better cooked. Overall, 1-2 cups of vegetables per day minimum should be consumed.