In the Tables section of this booklet, you will find Table 1: Nutritional Content of Many Fruits and Vegetables, and Table 2: Calcium to Phosphorus Ratios. (See Calcium and Phosphorus section.) Both will be helpful when choosing foods to fill the above categories. Although you may not understand the significance of many of the vitamins and minerals listed, (a few will be talked about later in this section) you will at least be able to tell which foods are high in calcium, and alternately, which seem to be deficient in most vitamins and minerals listed. As an exercise, compare arrowhead or lettuce to other vegetables - you should be able to tell that neither stacks up to most other food items listed. Foods largely deficient in nutrients should be avoided, as iguanas are only able to extract about 40% of the nutrients from the foods they eat. That, coupled with the limited space iguanas have in their stomachs, means that only foods rich in vitamins and minerals should be chosen as staple items in your iguana's diet.

The Specifics

Keeping those basic guidelines in mind, there is some more very important information that you need to know. As you are probably aware, there are some foods that can cause problems in humans when eaten in excess. Not surprisingly, the same is true with iguanas. Humans are generally in charge of their own diets, and we tend to intake a wide variety of foods simply due to the fact that many different things are pleasing to our taste buds. Most people eat fruits and vegetables as well as meats, grains, and dairy products. Eating so many kinds of foods helps to ensure that all of our nutritional requirements are met. In addition, many of the foods that we eat often, such as bread and milk, are usually fortified with vitamins. We may conclude that most of us receive all of the vitamins and minerals necessary to sustain life through the foods we eat. (There are certainly exceptions.) Iguanas, however, are strict vegetarians. Some human vegetarians experience health problems because they do not eat enough different kinds of vegetables regularly. Iguanas, too, can be deprived of essential nutrients if they are limited to some particular group of low-nutrition vegetables that their owner has unwittingly chosen. Fortunately, much is known about the nutritional contents of fruits and vegetables, and about some nutritional requirements of iguanas, and you can use this information to sculpt a suitable diet for your iguana.

To help you choose, listed below is some important information about several groups of vegetables, some essential nutrients, and some nutritional requirements of iguanas. They should all be considered with equal importance and not ignored. Nutritional deficiencies are common in iguanas because many iguana owners are unaware of the nutritional content of the foods that they are offering their pets. Sometimes, even a varied diet can be a poor one if the wrong vegetables are chosen.

Calcium and Phosphorus

The food that you give your iguana, on average, should contain about twice as much calcium as phosphorus. A generally acceptable range of calcium to phosphorus ratios is between 1:1 and 2:1, but 2:1 is really ideal and a slightly greater ratio wouldn't hurt. (A 2:1 ratio indicates twice as much calcium as phosphorus, while a 1:1 ratio indicates the same amount of calcium as phosphorus. When we speak of this ratio, the calcium content is always written first, followed by the phosphorus content.) This ratio is very important for bone growth and maintenance, as well as for muscle contraction and many other important bodily functions. Metabolic bone disease, (see Metabolic Bone Disease section) as well as many other health problems, can be caused simply by ignoring this ratio for a short length of time. In addition, it should be noted that hypocalcemia (calcium deficiency) is much more common than hypercalcemia (excess calcium) in iguanas. This generally means that iguana owners tend to upset the Ca:P ratio by depriving their lizards calcium, not phosphorus. If you take a look at Table 2: Calcium to Phosphorus Ratios, you will see why. Only about one third of the foods listed contain as much calcium as phosphorus. When choosing foods for your iguana, try to stick to those foods that have at least a 1:1 ratio. Again, a ratio of 2:1 is ideal.

The items in Table 2 are listed by their Ca:P ratios, in descending order. The information in this table has merely been excerpted from Table 1, but it has been included so that you can find the better calcium sources faster. The foods which contain Ca:P ratios of less than 1:1 are included because you will probably find yourself using low calcium fruits or vegetables due to availability in your area, and I wanted to give you an idea of just how calcium deficient many of these foods are. By knowing how calcium deficient a particular food item is, you can choose additional foods with high calcium content to try to keep the ratio in the proper range. The portion sizes are not included in this table. Table 1 is a more complete table of food values, and you may refer to it for portion sizes. With the portion sizes in mind, you can actually calculate exactly how much calcium and phosphorus you are serving your iguana at each meal. Most iguana owners do not wish to do this chore, understandably! In fact, it is not usually necessary. What you must bear in mind, however, is the approximate RATIO of the calcium and phosphorus contents. One cup of pineapple pieces, for example, contains 11 mg of calcium and 11 mg of phosphorus. That is an 11:11, or 1:1, ratio. This means that any serving of pineapple, whether it be one cup or one whole pineapple, will contain this ratio of calcium to phosphorus. This allows you to at least approximate what Ca:P ratio is present in the foods your iguana is eating. For example, if one day you feed your iguana a diet consisting of pear, green beans, mustard greens, endive and prickly pear, you will notice in the table that they all have Ca:P ratios between 1.06:1 and 2.32:1. Therefore, your iguana's diet will contain a Ca:P ratio somewhere between those two, which is satisfactory. (Remember, 2:1 is ideal!) And understand that if you offer a heaping portion of some calcium poor item and only a couple leaves of a calcium rich item such as collard greens, you're probably still offering a calcium poor meal. If you stick to the first 66 fruits and vegetables listed in the table, which are the ones with ratios of 1:1 or higher, you will have less chance of running into problems stemming from hypocalcemia. Do not stick to the very highest end of the table only, however, as a diet containing too much calcium can cause hardening of the soft tissues due to calcium deposits. This problem can be just as serious as calcium deficiency.

I would also like to point out the importance of another nutrient, vitamin D3, at this time. Vitamin D3 plays a crucial role in calcium absorption: your iguana will not be able to use the calcium it ingests if vitamin D3 is not also present. Vitamin D3 can be obtained through exposure to natural unfiltered sunlight (see Ultraviolet Light section,) and it is also found in the food your iguana eats. At this time, however, it is speculated that iguanas may have difficulty extracting vitamin D3 from food sources, which makes ultraviolet light even more important.

Calcium deficiency is probably the leading killer of iguanas in captivity. But remember, a diet abundant in calcium will do your iguana no good if the calcium to phosphorus ratio is not correct, and it will also be a useless mineral if vitamin D3 is not present - a vitamin most easily obtained through exposure to unfiltered sunlight (see Ultraviolet Light section).

Oxalic Acid

It is known among nutritionists that oxalic acid, a chemical found in many plants of the genus Oxalis, binds with calcium to form calcium oxalate, an insoluble salt. This seemingly obscure fact is a much overlooked, but very important, point to address when tackling iguana nutrition. What that scientific jibberish means is that when you or your iguanas eat food high in oxalic acid such as spinach, rhubarb, beets, beet greens, celery stalk or swiss chard, the oxalic acid binds with the calcium in these vegetables, rendering it unusable. In even simpler terms, eating any of those six vegetables in excess can cause calcium deficiency. In humans, this may not be as important because most of us eat varied diets, not usually restricted to vegetables such as these. But because we are generally used to feeding our other pets a single food item such as canned cat or dog food, it is not difficult to see how some iguanas might end up being fed a diet consisting largely of, for example, spinach, which actually has a high calcium to phosphorus ratio but still contains this nutrient antagonist, oxalic acid. Most people are unaware that this seemingly nutritious vegetable also contains this chemical which binds up that calcium and deems it unavailable. As a matter of fact, there is enough oxalic acid in any given portion of spinach to bind with all of the calcium present in that portion, and then some. The lesson? Do not include spinach, rhubarb (which is actually considered to be toxic to iguanas; see Toxic Plants table,) beets, beet greens, celery stalk, or swiss chard as staple items in your iguana's diet. My piece of advice is to offer these six foods in only very small quantities, if at all. Certainly, if the grocery store is out of your favored greens, a few servings of spinach will not harm your iguana. But you must understand that you should not offer any of these foods on a daily basis, or even half of the time. Iguanas in captivity are exceptionally adept at developing metabolic bone disease, and it is speculated that the excessive feeding of these foods is one of the reasons for that.

Goitrogenic Cabbages

Like oxalic acid-rich vegetables, many vegetables in the genus Brassica (the "cabbage-like" vegetables) should not be fed in excess. Cabbage, kale, bok-choi (Chinese cabbage,) broccoli, turnips, rutabaga, cauliflower, and brussels sprouts can all cause thyroid problems in iguanas (as well as humans) if too much is consumed. In short, do not use any of the eight aforementioned vegetables as staple items in your iguana's diet. They can cause metabolic problems eventually if fed in excess. It should be noted, however, that not all members of the Brassica family posess such harmful qualities. Collard greens and mustard greens are two Brassicas that are considered to be good for iguanas. At this time, it is believed that only the few items listed above should be avoided.

Tannins

One last group of foods that is generally recognized by those of us who are concerned with iguana nutrition are foods that contain large amounts of tannin. Tannin binds protein, fights digestion by inhibiting key enzymes involved, and can also render iron and vitamin B12 unavailable. If served in excess, foods high in tannin can damage the liver. Foods that contain relatively large amount of tannin are spinach, carrots, bananas, grapes, lettuce, rhubarb (which is, once again, considered to be toxic to iguanas and should not be offered anyway,) and onions. Offering foods containing high amounts of tannin is not recognized as being as dangerous as, for example, offering foods like spinach which contain high amounts of oxalic acid; this information is simply included to deter you from feeding your iguana a diet consisting of only the food items listed above. In addition, I wanted to reiterate the importance of offering your iguana a very varied diet, which can help reduce the possibility of your iguana running into health problems.

Cat and Dog Foods

As was mentioned earlier, many herpetologists now believe that captive iguanas of all ages should be offered the same type of diet. It was once widely believed that juvenile iguanas needed much more protein in their diets than adults. Thus, juvenile iguanas were offered foods such as commercial cat and dog food, insects, and cooked meats. Although I still recommend more vitamin supplementation for juvenile iguanas than adult iguanas (see Vitamin and Calcium Supplementation section), I no longer recommend offering such increased protein to juveniles. Examination of the stomach contents of wild iguanas indicates that iguanas of all ages are folivores, and not omnivores as many used to believe. Certainly, your iguana may relish the high protein foods listed above, and iguanas in the wild will indeed eat the occasional insect. Under no circumstances, however, should these foods become a large part of your iguana's diet. Even most herpetologists who still recommend offering increased animal protein in juvenile diets agree that protein-rich foods should only comprise a very small portion of the diet - around 5% total. If you feed your iguana a balanced vegetable diet complete with vitamin and calcium supplements, it should live a healthy life without these extra foods. Occasional treats that stray from the basic vegetarian diet should not harm your iguana, but "occasional" means not every other day, but perhaps once every few weeks. Autopsies on iguanas that have been fed cat and/or dog food throughout their lives reveal badly damaged livers. It is simply unneccessary to offer your iguana foods such as these when proper food items are available at any grocery store.

Commercial Iguana Diets

The manufacturers of commercial iguana diets claim that their products contain all of the nutrients essential to the survival of green iguanas. It is recommended by some veterinarians that offering one of these formulated diets, without too many supplemental vegetables (which would throw off the nutritional balance present in the formula) should be fed to any iguana that will eat it. However, there are anecdotal cases in which groups of iguanas that were given these diets exclusively developed dietary deficiencies within a year. In addition, there is no documented RDA (recommended daily allowance) for iguanas. It is difficult to see how any of these diets could have been formulated without the guidance of an RDA, yet these diets remain on store shelves. The conclusion of many veterinarians and herpetoculturists is that commercial diets are very new and insufficient research and experimentation has been done with them. My recommendation is that you do not restrict your iguana to a commercial iguana diet, but rather offer a nice variety of vegetables and leafy greens, which is what iguanas eat in their natural habitat. If you have some sitting around, feel free to use commercial iguana food products on those infrequent days when you realize that you are all out of greens and really don't have time for a trip to the grocery store. In addition, they are handy for those weekend trips when you hire a pet sitter or when you take your iguana with you and don't want to take a cooler full of fresh vegetables. But on a daily basis, offer your iguana what it instinctively eats in the wild: leafy green vegetables. And if you ever do offer your iguana the dry commercial food, do make sure that there is plenty of fresh water available because iguanas obtain most of the water they need from the vegetables they eat. Most commercial diets contain virtually no water at all, and as you may know, water is essential to most life forms on Earth.

What About Pizza or Leftover Chinese Food?

Many iguanas relish non-vegetarian items. Do not panic if you return to your living room one evening to find that your iguana found its way into the pizza box that you left on the table earlier. Just as we eat candy bars, items which contribute nothing beneficial whatsoever to our bodies, iguanas can have an occasional bite of pizza, cashew chicken, or even ice cream. (I might add that chocolate is known to be toxic to birds and dogs, and I do not know whether any research has been done with chocolate and iguanas. Please do not attempt such research at home.) Just make sure that nutritious vegetables make up the bulk of your iguana's diet. You would not feel very well if half of the food you ate were candy, but an occasional snack wo't hurt. (Please refer to the definition of "occasional" in the Cat and Dog Foods section.)

The Good Stuff

The good news is that, believe it or not, there are still many vegetables left that are beneficial to your iguana. Collard greens, parsley, dandelion greens and green beans are some of the favored foods for iguanas among herpetoculturists. If you refer to Table 2, you will see that they all have calcium to phosphorus ratios over 1:1, and if you read the last few pages you know that none contain much oxalic acid or are of the cabbage-like vegetables that tend to cause thyroid problems. In addition, they are all relatively high in many essential nutrients.

Some foods that are currently recognized as being good choices for an iguana diet are listed below. Remember to avoid foods high in oxalic acid, such as spinach, rhubarb, beets, beet greens, celery stalk and swiss chard, to avoid cabbage-like foods which can lead to thyroid problems, such as cabbage, bok-choi, kale, rutabaga, turnips, cauliflower, brussels sprouts, and broccoli, and to offer a selection of foods that contains, on average, a calcium to phosphorus ratio of 2:1. You can certainly offer the undesirable foods in small amounts, intermittently. But considering the wide variety of other vegetables available to us, it is best if you stay away from such problematic foods.

A good basic diet for iguanas: collard greens, turnip greens, mustard greens, parsley, dandelion greens, rapini, green beans, figs (raw or dried), green peppers, escarole, raspberries, leeks, snow peas, blackberries, grapes, radish, okra, pears, pricklypear, parsnip.

Remember, just because a food item is on the above list does not mean that you can choose it plus just one or two other items and serve them only. The list is only of any use if you try to use many of, all of, or more than the items on it. I usually challenge iguana owners to try to pick out fifteen varieties of foods for their iguanas when they go to the grocery store. You must pick and choose which combinations are the best, depending on what is available in your area, what your iguana likes and dislikes, and even price. It should be noted that some iguanas like variety in their diet, and will tire of the same old items. Some iguanas, however, do not respond well to new food items so if yours stops eating when new items are introduced, revert to the old but make sure that the diet is well-rounded! So take a look at the above list, and take a look at Table 1 and Table 2. Use the knowledge you have just obtained about nutrient antagonists and formulate your own iguana diets daily. DO add nutritious items to the above list that have been overlooked. My goal in writing this booklet is not to force its readers to memorize by rote which foods should be offered and which should not, but to teach people how to formulate their own diets for their iguanas, based on the information I have given. I cannot simply prescribe a diet; rather, I want to help you formulate your own.

Vitamin and Calcium Supplementation

Despite our efforts to offer varied, nutritionally complete diets to our iguanas, iguanas still sometimes wind up with nutritional deficiencies. This is generally due to the fact that the foods that iguanas eat in the wild are simply not available to us. Iguanas have evolved to live in areas which furnish exactly what iguanas need to survive, while the foods you may choose in the grocery store simply may not. For this reason, people sprinkle vitamin and mineral supplement powder on top of their iguanas' food to help round out their diets.

Because juveniles are such rapidly growing animals, it is generally recommended that they be given more supplement than their adult counterparts. As a general rule, mix a small pinch of supplement in with the food at every other feeding. For adults, a larger pinch once or twice a week should suffice. Do not go overboard with supplementation. Do not feel the need to coat each piece of food with vitamin or calcium powder! Just a very light sprinkle over the top of the food is fine. If you have multiple iguanas, you may wish to mix the supplement in with the food so that the first iguana to attack the food bowl doesn't end up eating all of the supplement powder.

There are several supplement choices on the market, so you may not know which one(s) to choose at first. I have very specific recommendations:

1) I recommend you crush up a human multivitamin such as Centrum and use it as the basic vitamin supplement. Alternately, you should choose a commercial reptile vitamin supplement which contains beta carotene rather than vitamin A because vitamin A can cause problems in excess while beta carotene is converted to vitamin A as needed;

2) You should use a calcium supplement which contains only calcium and vitamin D3. A supplement containing phosphorus should not be used because such a supplement does little to counter balance the high levels of phosphorus present in most vegetables.

You should learn to estimate the calcium and phosphorus levels in your iguana's diet. Just look at the foods you have offered, look at Table 2, and decide if the diet is calcium rich or calcium poor, relative to its phosphorus content. If you are offering a lot of collard greens, for example, which have an extremely high Ca:P ratio, you may need to use little or no calcium supplement. If the diet seems to be in between 1:1 and 2:1, you may choose to use supplementation only once in a while. If for some reason you are unable to purchase foods that have a Ca:P of 1:1 or greater, you must use supplementation regularly, and you must also find a better source of food items! Be careful, but do not worry too much about overloading your iguana with vitamins and minerals, as hypervitaminosis is hardly ever seen in iguanas, while vitamin deficiencies are seen all the time.

Water

Like most living systems on Earth, iguanas need water in order to survive. Iguanas can live for a long time without food, but will perish quickly if deprived of water. It is important that you provide a water bowl in your iguana's enclosure so that it may drink when it wishes to. It is also important to keep it clean. Iguanas often choose to defacate in their water bowls, and they will also bathe in it if it is big enough. Considering the high temperatures that must be maintained in your iguana's habitat, (see Heating and Lighting section) the water bowl can become a breeding ground for bacteria. It is a good idea to change your iguana's water daily, plus whenever you see that it has been soiled.

Many people comment that they never see their iguanas drinking from the water bowl. This is because most do it very infrequently. Vegetables are comprised of mostly water - above 90% in many cases. Thus, your iguana will obtain most of the water that it needs from its food. You must still provide a water source, however, as your iguana will still need more water than its food can provide. Your iguana will be especially thirsty on days that it hasn't eaten or on days that it has eaten dry food, (such as a commercial iguana diet) so do not neglect your iguana's water bowl on these occasions.

When to Feed

As a general rule, iguanas should be fed on a daily basis. It has been reported in many different publications that adult iguanas can be fed every other day or just a couple times a week, but in this author's experience, iguanas simply eat more and more as they mature. Iguanas not fed on a daily basis become restless and give me the "iguana glare" when not kept fat and happy. In addition, iguanas do not seem to have a tendency toward obesity and can be fed essentially as much as they wish to eat. So you can basically offer your iguana all that it will eat, and simply make sure that it is not undernourished.

A good time to feed iguanas is in the late morning. After your iguana's light and heat sources are turned on in the morning, (see Heating and Lighting section) it will need one or two hours to "warm up"before it is interested in food. In between 9AM and 11AM would be a good time to feed your iguana, depending on the season. (See Photoperiod section). If you work or go to school during the day, you generally have two choices: feeding your iguana in the early morning or in the evening. The early morning is a much better choice than the evening. In the wild, iguanas would be done with their daily routine by late afternoon. At least if you offer the food in the early morning your iguana can choose to eat it later. If there is no food all day, your iguana may become stressed, which can lead to physical illness.

Monitor your iguana's physical appearance on a daily basis and note the appearance of its sides. There should not be pronounced flaps of skin running down the sides of your iguana. If there are, your iguana might not be getting enough food. Try offering it more at lunchtime. In addition, the base of your iguana's tail should always be round and plump, not emaciated looking. If a larger lunch does not seem to help your iguana's thin appearance, refer to the section of this booklet entitled Illnesses, which deals with some common problems in iguanas.

How to Feed

You should decide how small to chop up your iguana's food based on its size. The basic idea is that you want your iguana to have as little trouble as possible while eating. This is especially important with harder or more awkward-shaped vegetables. You may notice that although your iguana has lots of nice, sharp teeth, it does not exactly chew its food. Most of it is swallowed whole. Some people decide to use a food processor to chop up all the food offered to their iguanas. When the food is shredded in such a way, there is little chance that an iguana could choke on its meal. Also, the digestive system of the green iguana is not especially efficient. By chopping food up into more, smaller pieces, you provide more surface area to the food which makes it easier for your iguana to extract nutrients. Use whatever method is best for you to ensure that your iguana will easily be able to swallow and digest its food.

In addition, you should mix up the food thoroughly. Iguanas do have favorite food items, and when it is not mixed well they can easily pick out the foods they like best and leave the rest. This can be dangerous because iguanas need a varied diet in order to obtain all the nutrients they need for survival. If your iguana picks out one or two food items only, it is not getting a varied enough diet. This is probably the best argument for using a food processor, because such a machine can blend the food together so well that one item becomes indistinguishable from the rest. I simply use a knife to chop up food for my iguanas, but I offer relatively small amounts of each type of food. This way, even if the iguana does pick out its favorites first, it will still be hungry afterwards and be forced to move to the next item!

If you have multiple iguanas eating from the same plate, you should monitor each one's food intake to make sure that they are all getting a little bit of everything. Alternately, you could feed them separately.

Eating and Seasons

You will probably find that your iguana eats more in the summer months than in the winter. This is normal behavior. Even in the tropics cooler, dryer seasons exist, and at that time iguanas eat less. In addition, iguanas usually begin their mating season in what we would call autumn, and many animals tend to eat less during their mating seasons. (Males eat a lot prior to the mating season in order to build up fat stores, and then eat less when thinking about pursuing a mating partner. Gravid female iguanas eat less and less as their eggs develop, until they eat virtually nothing at all for a couple of weeks prior to egg laying. See From Breeding to Egg Incubation section.) So, if your iguana begins to eat less when autumn arrives, do not immediately despair. It is probably normal.