Nutrient Absorption vs. Recommendations
After my post Calcium Absorption from Greens, I got a question from a reader that I think many people may be wondering about.
She has been told to get 1,200 mg of calcium per day. But if the calcium from greens in only absorbed at less than 50%, does that mean she needs to get a higher amount of calcium in her diet so that she absorbs a full 1,200 mg?
The answer is that dietary recommendations are made knowing that a nutrient is only partially absorbed from the diet. It depends on the nutrient and recommendations are made for each nutrient based on its typical absorption rate.
In extreme cases, such as the calcium from spinach that is absorbed at only about 5%, you would need to make modifications to rely only on spinach or foods with a similar absorption rate. But the recommendations for calcium assume that only about 1/3 is going to be absorbed from the best sources (not sure the exact number the Institute of Medicine uses).
But this is a reason why I never mention getting one’s calcium from legumes or nuts and seeds – when you combine their relatively low amounts of calcium and their low absorption rates, you cannot rely on them for the bulk of your calcium needs. They will supply some, but not nearly enough.
Focus on the greens with higher amounts of calcium that is moderate to highly absorbable, calcium-set tofu, and fortified foods or supplements.