Certain foods contain compounds that are bad for box turtle health if they eat too much of them. These compounds prevent the turtles from getting enough of some of the other nutrients they need.
For example, a compound called oxalic acid binds calcium, which prevents your turtle’s body from absorbing the calcium. If she eats too much food containing oxalic acid she could end up with a calcium deficiency even if she’s eating a normal amount of calcium.
It’s important to limit foods containing oxalic acid and certain other compounds in your turtles’ diet, but don’t stress about it. Wild turtles eat whatever foods they find and don’t much care about calcium, oxalic acid or any other compounds. But they don’t suffer the same vitamin and mineral deficiencies as some captive turtles do, because they don’t eat a lot of any one food. By eating a wide variety of foods, they get the good nutrients from even the “bad” foods while avoiding the complications that arise from eating too much of one food.
You can help your pet turtle do the same.
Foods Containing Oxalic Acid
As mentioned, this compound binds calcium. The more your turtle eats, the less calcium he will be able to absorb. Since turtles need a lot of calcium, this can cause soft bones and other serious health problems.
Oxalic acid can also cause kidney problems, because when it combines with calcium it forms calcium oxalate. This compound is a crystal, and when these crystals form in our kidneys we call them “kidney stones.” Your box turtles can get kidney stones, too.
But foods that contain oxalic acid also contain other good nutrients, so it’s not necessary to avoid them completely, just use them sparingly. Here are some examples of foods high in oxalic acid:
- Swiss chard
The Oxalosis & Hyperoxaluria Foundation has a useful PDF called The Oxalate Content of Food. You can find the link for downloading the PDF about half-way down the page. It’s geared toward humans, so has a lot of foods you wouldn’t be feeding your turtles anyway, but it’s still a good reference for fruits and vegetables.
Foods Containing High Levels of Goitrogens
Here are some examples of foods with high goitrogen levels:
- Brussels sprouts
- Other cruciferous vegetables
Although you should definitely limit these foods, you can also lower the chance of problems from eating them by leaving a piece of cuttlebone in your turtles’ tank. It’s a good source of extra calcium, but it also contains trace amounts of iodine.
Foods Containing a Low Calcium to Phosphorus (Ca:P) Ratio
When your box turtle doesn’t get enough calcium in her diet, her body will take some from her bones to maintain her blood Ca:P ratio at the right levels. This level is about 2:1, so she needs about twice as much calcium as phosphorus. The best way to keep your pet’s Ca:P ratio balanced is to feed mostly foods with more calcium than phosphorus. When you do use foods with a low ratio, sprinkle them with a calcium supplement (one without phosphorus, of course).
Here are some foods with low Ca:P ratios:
- Sweet potato
- Broccoli (one more reason to use it sparingly)
As you can see, a lot of these are fruits, which many box turtles love. Remember, you don’t need to deprive her of her favorite treats, just don’t make them a daily habit and make sure you supplement with calcium.
Most lettuce, especially iceberg lettuce, contains very few nutrients. It is a good source of fiber, but since other foods packed with nutrients also supply fiber, this is not a good reason to feed much of it. Since your turtle can eat only small amounts of food, you want that food to pack as many nutrients as possible into a small volume. Of course, many turtles are quite fond of lettuce, so just like the other foods mentioned, feed it in small quantities.
Even so-called “bad” foods contain a lot of valuable nutrients, like trace minerals and vitamins (especially beta-carotene, C and K). They’re also great sources of fiber. So don’t cut them out of your box turtle’s diet completely, just remember that variety is the key!