Here are examples of things he can eat:
Fruits: apples, pears, grapes, watermelon, canteloupe, honeydew, berries, peaches, cherries, mango, papaya, nectarines, kiwi.
Veggies: Corn (limited), peas, green beans, carrots, zuchini, sweet potato, broccoli, spinach, spring mixed greens, squash, garbanzo beans, cucumber, tomato (limited-I guess that should be with fruits)
Proteins: baked chicken (plain or soaked in apple juice before baking/broiling), very lean beef plain, turkey baked/broiled (not deli meat or meat sticks), egg (mine love it mixed w/spinach), cottage cheese, yogurt, tofu (very limited)
You should get some vanilla or berry Ensure to keep on hand too. Jarred baby food is OK in a pinch but CANNOT have onion or garlic. Also watch for salts and preservatives.
Limit nuts. They are very fatty and should be raw or roasted without salt or seasonings.
He needs to have some from each group every night. Without proper diet, he will not live a long life at all. It does not matter how they "appear" on the outside. Gliders hide sickness normally until it's too late, unless their owner is VERY observant.