Wednesday, April 7, 2010

More stuff you didn't know about calcium

Annyca asked about the calcium in skim milk and almonds. Before I respond to that, see how you go with this question.

Which has the greatest amount of calcium per serve?

a. Milk, reduced-fat, 200 mL glass

b. Yogurt, low-fat, 200 mL tub

c. Soy milk, 200 mL glass

d. Cheese, cheddar 30g slice

e. 30g almonds

(For our US friends: 200 mL = 7 fl oz approx; 30g = 1 oz approx)

The answer in my part of the world is (b) because:

A glass of reduced-fat milk has around 300mg of calcium;

200 mL low-fat yogurt (340-450 mg);

A glass of soy milk (60-230 mg);

30g cheddar cheese (200 mg); and

30g almonds (70 mg).

Previously, I told you that spinach was not a great source of calcium. That’s because the calcium is tightly bound to oxalic acid forming calcium oxalate, which cannot be split by digestive enzymes, therefore the calcium is not absorbed into the body. The same happens with the iron in spinach (it’s called ferrous oxalate). You get to absorb about 5% of the calcium and 2% of the iron in spinach. On the other hand, spinach is great for folate.

You will see from the figures I gave for soy milk that the calcium levels can range from 60-230mg in a 200 mL glass. Soy is not a good natural source of calcium. I suggest choosing a calcium fortified soy milk which will give closer to the 230 mg in a glass. A US study found that calcium in soy milk was absorbed only 75% as well as calcium in cow milk. It was not clear why.

Hannah and John had some questions about the type of milk. Skim milk in Australia generally has one and a half times more calcium than full cream milk. The fat in full cream milk (and any fat in your diet) may slightly reduce calcium absorption, so that could be an extra bonus in going for skim milk – more calcium and easier to absorb.

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