The Green Iguana (Iguana iguana) has become a popular pet reptile, but maintaining its long-term health depends entirely on a precise, plant-based diet. Iguanas are strict herbivores that have specialized digestive systems, relying on microbial fermentation in their hindgut to break down tough plant cellulose. Providing an improper diet is the most common cause of illness in captive iguanas, often leading to severe and preventable conditions like Metabolic Bone Disease (MBD) or kidney failure. Understanding the correct food types, ratios, and preparation methods is essential to mimic the nutritional complexity of their natural foraging habits.
Daily Dietary Staples: Greens and Vegetables
The foundation of a Green Iguana’s diet must be dark, leafy greens, which should comprise approximately 80–90% of their total food intake. The primary factor in selecting greens is the calcium-to-phosphorus (Ca:P) ratio, which must be at least 2:1 to ensure proper calcium absorption and bone health. Calcium-rich options that meet this requirement include:
- Collard greens
- Mustard greens
- Turnip greens
- Dandelion greens
- Escarole
These greens should be rotated frequently to provide a broad spectrum of nutrients. Secondary vegetables can make up 10–20% of the diet, focusing on brightly colored items that offer diverse vitamins. Excellent choices include various squashes, such as butternut, acorn, and spaghetti squash, as well as sweet potato, bell peppers, and green beans. These items should be finely chopped or grated to encourage ingestion and prevent selective eating.
Fruit must be limited to a minimal amount, making up no more than 5–10% of the overall diet. While iguanas enjoy the taste of fruit, the high sugar content can disrupt the balance of their gut flora and contribute to obesity. Fruit should be considered an occasional treat or a topping to encourage the consumption of less palatable greens.
Items That Must Be Strictly Avoided
A common misconception is that iguanas need animal protein, but feeding them any form of meat, insects, or dairy is detrimental to their health. Iguanas are hindgut fermenters whose bodies are not equipped to process the purines found in animal protein efficiently. Consuming high-protein items, such as dog food, cat food, or commercial insect matter, forces the kidneys to work overtime to excrete the excess nitrogenous waste. This chronic strain frequently leads to hyperuricemia and premature kidney failure.
Certain plant foods also pose nutritional hazards and should be excluded or fed only in tiny amounts. Foods with a poor Ca:P ratio, where phosphorus outweighs calcium, inhibit calcium absorption, which can lead directly to Metabolic Bone Disease. These include high-phosphorus foods like corn, peas, and bananas.
Other greens contain natural compounds that interfere with nutrient uptake. Spinach and parsley are high in oxalates, which chemically bind to calcium in the digestive tract, preventing the lizard from utilizing it. Similarly, goitrogenic vegetables like kale, broccoli, and cabbage contain compounds that can interfere with thyroid function by binding iodine, potentially causing hypothyroidism if fed excessively. Toxic items like avocado and rhubarb must also be strictly avoided due to known toxicity in reptiles.
Preparation and Nutritional Supplementation
Proper food preparation is essential for a captive iguana, as it directly impacts digestion and nutrient uptake. All food items must be thoroughly washed to remove pesticide residues before being finely chopped or shredded into manageable pieces no larger than the space between the iguana’s eyes. This small size ensures the lizard cannot pick out preferred ingredients and helps the digestive microbes access the plant matter more easily.
Because iguanas are often housed indoors without access to direct, unfiltered sunlight, they require supplementation to prevent nutritional deficiencies. A pure calcium carbonate supplement, which should be phosphorus-free, is the most important additive. This calcium powder should be lightly dusted onto the food every day for juveniles and three to five times per week for adult iguanas.
Vitamin D3 is necessary for the iguana to process and absorb the dietary calcium, but it must be provided carefully. While the iguana ideally synthesizes its own Vitamin D3 from exposure to a UVB lamp, a multivitamin containing D3 may be lightly dusted onto the food once or twice a week. Adults should be fed once daily in the morning, which aligns with their natural temperature cycle and allows them a full day to bask and digest the meal. Hydration is also supported by misting the enclosure or providing a large soaking pan, as iguanas often drink water droplets rather than from a standing bowl.