• 1. The Natural History of Green Iguana Digestion


• 2. Feeding Ethics


• 3. Dietary Adjustment


• 4. Feeding Schedule


• 5. Edible and Toxic Plants


• 6. Construct of a Well Balanced Diet


• 7. Basic Diet and Preparation


• 8. Nutritional Disorders


• 9. Popular Iguana Links


• 10. Acknowledgments

Green iguanas (Iguana iguana) are large semi-arboreal to arboreal lizards of the primarily New World Americas. They are almost an exclusively herbivorous reptile. Earlier beliefs were that the juveniles were insectivores, and then gradually grew into herbivorous adults. However recent studies on stomach content in wild iguanas have revealed that this is not the case. Iguanas are born herbivores and do not go through an ontogenetic shift from insectivore to herbivore. The digestive system is therefore designed to digest plant materials and not, as some recommend, to digest meat in any amount. The green iguana has evolved an elaborate hindgut, housing a microbial fermentation system that allows it to utilize fiber as effectively as mammalian ruminants. The adult iguanas spend most of their time in the upper parts of the trees, while the juveniles are either on the ground or in the lower parts of the trees and bushes. Due to the iguana's habitat, its wild diet consists of a variety of leaves, small fruits and flowers - and this variety should be provided in captivity as well. It may sound easy to provide a varied diet for the captive iguana, however the diet must also be a nutritiously balanced and healthy diet and this is why the iguana owner needs to learn some basic guidelines for making a proper Iguana-salad.
Photo by Chris Estep

Iguanas don't recognize what we are trying to feed them as being proper food. They are attracted by certain shapes and colors, and may, like humans, get 'hooked' on junk foods, foods that either lack nutritional value or that are downright harmful to them, or foods that they are simply used to getting. This is a particular problem with pre-owned iguanas, iguanas being fed less than ideal diets, and those who have come from pet stores where they have been fed the generally inappropriate feed usually fed to them. One needs to learn how to deal with this syndrome, how to be patient, not give in, and eventually be rewarded with your iguana eating what it should!

There is no simple answer as to what is the best diet for iguanas. Green iguanas are hardy and extremely adaptable and will fare on a wide variety of different diets as long as they all meet a certain basic criteria. When keeping an iguana as a pet, one of the best ways to adjust the diet is to look at the veterinary problems with the associated with the diet at different stages in an iguana's life.

• In juvenile and immature animals primarily during the first two years but also up to the ages of 4-5 years, one of the most common problems associated with diet that veterinarians encounter is metabolic bone disease, caused by a lack of usable calcium. Green iguanas grow at a truly remarkable rate from hatchlings to sexual maturity, approximately a 100 fold increase in weight in 3 years. This implies very rapid growth of all body structures including the skeletal system which will require large amounts of usable calcium.

• A diet higher in protein content will allow an iguana to maximize it's potential growth during the first two years. There is evidence from observations of juveniles both in the wild and in captivity, that given the opportunity, they will seek a higher protein diet such as insects and possibly carrion.

• Once sexual maturity is reached (2-3 years), growth slows down somewhat but continues at a fair rate for another year or two. In females during breeding, extra demands are placed for the production of eggs and for calcification of egg shells.

• At 4-5 years of age, the growth rate tapers drastically and the diet should be adjusted accordingly. One of the more common problems in older iguanas that are brought to veterinarians is visceral gout caused by the deposition of uric acid in the kidneys and other internal organs. This is a result of a diet too high in protein, particularly organ meat products.  Another common problem usually seen in male iguanas upon autopsy is metastatic calcification, the deposition of calcium in the internal organs. Both of these conditions are fatal and can be prevented through proper diet.

For juveniles up to 2½ years of age:

Feeding Schedule: Daily. Twice daily or continuous availability for hatchlings.
Diet: 85-90% plant matter
        10-15% animal protein sources and/or commercial pet diet
Vitamin/Mineral Supplementation: One small pinch of vitamin/mineral supplement per animal,
                                                     no more than once a day.

For iguanas 2½ years and up:

Feeding Schedule: Every 1-2 days
Diet: 95% plant matter
        5% animal protein sources and/or commercial pet diet
Vitamin/Mineral Supplementation: One full pinch per 2 lbs twice a week or 1/8th of a
                                                     teaspoon per 3-4 lbs of body weight per week.

Note: For mature females, increase calcium supplementation and protein sources
          (up to 15%) starting in late December and through egg-laying.

Before you go about preparing a salad for your iguana, one of the first things the you as an owner of an iguana needs to learn is to distinguish between "good" and "bad" food. The "good" foods are those food items that can be fed on a daily basis, ones listed in the Basic Iguana Diet.  If you plan to have the iguana free roaming in the house it is a necessary to find out what plants can be placed in the home. Only those that are non toxic should present.  Please refer to Melissa Kaplan's Edible Plants page to determine which house plants are safe to have accessible to the iguana.
There are also those plants which should either be avoided or only be used occasionally (ones every other week).  Some of these include: spinach, romaine lettuce, onions, beets, beet greens, celery stalk, Swiss-chard, carrots, bananas, grapes, lettuce, kale, Chinese cabbage, broccoli, turnips, cauliflower and brussels sprouts.  However there are some plants that are to be avoided all together. These plants are not edible and may have severe toxic consequences for the animal. Rhubarb is extremely toxic because of the formation of calcium oxalate crystals. For a complete list of plants toxic to iguanas and their pathways of toxicity, please refer to Melissa Kaplan's Harmful Plants complete listing. However, if you would like to view the plants for visual identification you can see the plants at the Cornell University pages of Poisonous Plants. If your reptile does ingest something it should not have, watch it carefully for signs of distress. Signs will usually include respiratory changes (i.e. rate of breathing increases or decreases, breaths become shallower or deeper, breathing becomes labored or difficult), increased salivation, dry heaves, vomiting, lethargy, increased activity, rubbing mouth on ground or other surfaces, scratching at face or mouth, diarrhea or other alteration of feces. Don't wait to see if the signs will abate - call (or have someone call) your regular reptile vet or emergency reptile vet (have these numbers and locations on hand before you need them) and let them know what the animal ate, what the signs are, and that you are on your way.  The National Animal Poison Control Center may also be able to offer you pertinent information, but in a potential emergency where time is of the essence, you should get your reptile to a vet who can administer an antidote and supportive therapy as quickly as possible. 

Calcium Rich Vegetables, where the Ca : P > 2 - 35% or more of the diet.

• Collards,  mustard greens, alfalfa chow or pellets, dandelions, bok choy, swiss chard
• Beet greens, escarole, green beans, turnips

• Note: Kale and bok choy in small amounts only.

Other Vegetables: A variety weekly - 35% or more of diet.

• Romaine lettuce, frozen mixed vegetables (thawed), shredded squashes, zucchini, sweet potatoes
• Bell Peppers, various sprouts, grated carrots, okra, cooked sweet potatoes

• Note: Broccoli, cauliflower, brussel sprouts and other members of the cabbage family should be fed in small amounts because they may cause thyroid problems when fed frequently in large quantities.

Grain/Fiber sources: Optional - up to 20% of diet.

• Mixed grain bread and natural bran cereal

Fruits: Offer a variety weekly - No more than 15% of diet.

• Calcium Rich: Fresh or dried figs, papaya, raspberries
• Other: Melons, apples, plums, peaches, strawberries, tomatoes, bananas, grapes, kiwi

Animal Protein sources: Up to 15% for hatchlings and sub adults. No more than 5% of adult diet.

• Note on primate diets: If it weren't for the high D₃ content, these diets could probably make up a substantial percentage of an iguana diet but the high D₃ content in combination with calcium will cause metastatic calcification in mature iguanas. Thus they should be used in moderation.

Deficiency/ Metabolic Bone Disease
Causes:
Calcium deficiency is the lack of physiologically available calcium. Simply supplementing the diet with calcium will not assure that the calcium will be absorbed through the lining of the intestine and become usable. For the effective absorption of calcium through the intestinal lining an adequate amount of vitamin D₃ and the proper calcium/phosphorus ratio is required. It is recommended that in iguanas that minerals be provided in the ratio of 1 part D₃ to 2 parts calcium to 1 part phosphorus.  These can be added in the form of vitamin supplements such as Rep-Cal^® and Terrafauna Vitalife^® using the proper dosage.
Secondary Causes:
Calcium deficiency can also be caused by the excessive feeding of oxalic acid. When ingested, oxalic acid has a high affinity for blood calcium. This causes a reduction of calcium levels as well as the formation of a potentially lethal, insoluble substance Calcium Oxalate. Refer to Melissa Kaplan's chart on the oxalate to calcium ratio of selected iguana foods to determine a suitable diet for your pet.  Acute cases of ingestion of high levels of oxalic acid is potentially lethal. The deposition of the crystals in the kidneys will cause blockage, necrosis, and ultimately death. One plant to avoid at all costs is Rhubarb. The high content of oxalic acid in the rhubarb leaves are toxic will kill even the largest of the iguanas. 
Symptoms:
The symptoms of metabolic bone disease will vary depending on a number of factors, such as the age of the animal and duration of the disease. In juveniles, symptoms can include a soft lower jaw and deformities of the back and legs. In larger animals, osteoporosis and fibrous osteodystrophy may occur. These are characterized by the swollen, smooth appearance of the hind limbs and swollen lower jaw. Animals with fibrous osteodystrophy are often initially perceived as rotund, fat animals until they manifest abnormal behaviors, usually the result broken limbs and bones now too weak to support the weight of the animal. Fibrous dystrophy results in swollen limbs due to the deposition of scar tissue around the ever-weakening and thinning bones to make up for the structural weakness.