Although it takes about five cups of cooked snap beans to equal the calcium in one cup of milk, the rate of absorption was the same from both sources. The absorption rate from broccoli was about 5 percent higher. One cup of broccoli provides about one quarter as much calcium as a cup of milk. But the calcium in spinach was poorly absorbed because of a high content of absorption-blocking compounds known as oxylates. The youths absorbed magnesium from snap beans, spinach and milk at about the same rate.
Snap beans provide nearly as much magnesium as milk, but spinach provides nearly five times more.
In a related test, the researchers collaborated with University of Wisconsin plant breeders to assess 64 unique types of snap beans, looking for differences in calcium content. They found wide differences, indicating that calcium content has a strong genetic basis. This means breeders can develop snap bean varieties with extra calcium. In addition, the researchers found that younger, skinnier snap beans had significantly more calcium than older, fatter pods. A group of post-menopausal women experienced a significant drop in their work efficiency during a recent study in which their magnesium intake was reduced to a little more than half of the Recommended Dietary Allowance for three months.