Captive desert tortoises depend on their owners for a proper diet necessary for their health and longevity. They'll eat a variety of foods offered to them even if the foods aren't good for them. Desert tortoises require a diet that they'd have in the wild - high in fiber and low in fat, protein and sugar.
At least 80 percent of a desert tortoise's diet should consist of grasses and plants from its native habitat. Suitable grasses include alfalfa, bermuda and deer grasses, which tortoises will eat both fresh and dry. Suitable plants include dandelion, globemallow, nopals (Opuntia cactus) and plantain. Tortoises will eat not only leaves, but also shoots, stalks and flowers.
Vegetables, especially dark green, leafy vegetables, can be used for the remaining 20 percent of a desert tortoise's diet, as they're rich in vitamins and minerals. Suitable vegetables include carrots, green beans, endive, kale and turnip greens. Feed vegetables in a dish to prevent the tortoise from ingesting gravel or sand, which causes impaction or irritation in the digestive system.
Fruits can be fed sparingly as a treat; they contain too much sugar and starch, which disrupts the normal bacteria in a tortoise's digestive system. Suitable fruits include apples, pears and strawberries. Always remove the pit, seeds and stem of any fruit you offer.
Foods to Avoid
Avoid feeding your desert tortoise excessive amounts of vegetables high in oxalic acid, such as collards, spinach and parsely; oxalic acid binds to calcium and prevents it from being absorbed. Also avoid excessive amounts of broccoli, cauliflower and mustard greens, as they suppress iodine absorption. Do not feed the tortoise lettuce, as it has no nutritional value. Too much protein can cause liver and kidney damage, as well as shell deformations, so avoid feeding desert tortoises cat and dog food, soy, tofu and animal protein. Also avoid frozen and canned vegetables (too much sodium), bread, celery and dairy products.