Kids dread the green, leafy spinach on their dinner plates, pushing it around in circles in the hope that no one will notice that they are not eating it. Nonetheless, parents hold firm in their conviction that spinach is great for their kids, that it will help them grow strong (like Popeye, they say persuasively). Celebrity chefs have even come up with ways to sneak spinach into other foods that children enjoy, like brownies or muffins. After all, spinach is such a great source of iron that it must be worth getting kids to eat it any way you can.
We (well, really just Rachel) love spinach in many forms – in salads, cooked, in quiches – but once again, we need to bring a bit of science to the claims about the strength-giving powers of spinach. (Feel free to ban your children from reading this section of the book. Understanding the truth about spinach ends up disappointing fans of the sailor man.)
Spinach is routinely recommended as a good source of iron. Spinach does contain non-haem iron, the type of iron found in vegetables. For a vegetable, spinach is a relatively good source of iron. There are 1.9 milligrams of iron in a 60-gram serving of boiled spinach, and slightly more if you eat it raw. Most green vegetables have less than 1 milligram of iron in a serving. In comparison with foods that come from animals, though, spinach contains a relatively small amount of iron. If spinach does not really have all that much iron, how did it get this great reputation?
The buzz about spinach may have started back in 1870 when Dr E. von Wolf published a paper reporting that spinach had a remarkably high iron content. Unfortunately, Dr von Wolf did not have a good copy editor, and he ended up with a decimal point in the wrong place in his numbers. So he accidentally reported an iron-content figure for spinach that was ten times too high. It was probably because of these mistaken findings that spinach became Popeye’s miracle food in the 1930s. As described by Dr T. J. Hamblin in the British Medical Journal in 1981, some German chemists in 1937 (perhaps wanting to prove that Popeye had the wrong idea) decided to investigate the wonder vegetable and realized that Dr von Wolf ’s figures were wrong.
One might think that it is good enough that spinach has more iron than most vegetables. Surely spinach will still help you to build up your red blood cells and muscles. Unfortunately, the body has a harder time using non-haem iron, the type of iron found in spinach. It is generally absorbed pretty slowly. There are chemicals, like Vitamin C, which can help the body absorb this type of iron better. But there are also chemicals which make it even more difficult for the body to absorb this type of iron. And ironically, spinach actually contains one of these chemicals. Oxalate, a chemical that binds with iron and prevents it from being absorbed well, is found in spinach.
Another claim for spinach as a wonder vegetable is its high calcium content. Unfortunately, the oxalate in spinach causes problems for absorbing calcium too. Oxalate also binds to calcium and makes it harder for your body to absorb it. For example, your body can absorb 50 per cent of the calcium in broccoli, but it can only absorb about 5 per cent of the calcium in spinach.
In the end, you can force your kids to eat all the spinach that you want, but it is unlikely to have dramatic effects on their health and strength. Spinach is a great vegetable; it just doesn’t deserve any extra credit for providing lots of iron or calcium.