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.
April 1st, 2013 at 5:46 pm
Thanks for clarifying because I was wondering about it actually. Especially with minerals like zinc and iron, I find it confusing to know how much to get when calculating for absorption, but this clears it up!
Interestingly, I used to be iron deficient every yearly checkup growing up and in my teens. Of course, I ended up anemic and was very weak and sick. Even after treatment each year, I would test low for iron again. When I became vegan, for the first time in my life, I’ve managed to spend 5+ years without an iron deficiency. It’s great and always a good feeling when my tests come back stellar.
April 1st, 2013 at 5:55 pm
Nadine,
That’s good to hear that a vegan diet improved your iron status. I have an upcoming post regarding a vegan who had iron deficiency and how she cured it. I’m waiting on one final detail.
April 1st, 2013 at 11:29 pm
I take a supplement containing 250 mg of calcium every day. Do I need to eat greens for calcium, calcium-set tofu or fortified foods?
April 2nd, 2013 at 3:38 pm
dimqua,
You can check your calcium intake by creating a diet log at http://peacounter.com/. That will tell you if you’re getting 700 mg a day or not. 700 mg is the lowest amount I’d recommend.
April 2nd, 2013 at 5:00 pm
From: Present Knowledge in Nutrition (Paperback) by John W. Erdman Jr., Ian A. MacDonald.
One serving of milk (240g or 1cup) has 300mg of Calcium which is 32% absorbed resulting in 96mg of absorbable Calcium.
One serving of Chinese Mustard Greens (85g or 3oz) has 212mg of Calcium which is 40% absorbed resulting in 85mg of absorbable Calcium.
(To me a serving of 3oz of greens seems pretty small for a vegan diet.)
Contrast this with Spinach:
One serving of Spinach (85g or 3oz) has 115mg of Calcium which is 5% absorbed resulting in 6mg of absorbable Calcium.
April 2nd, 2013 at 5:14 pm
James,
According to the USDA Nutrient Database, I get that the mustard greens highest in calcium are the frozen and then boiled version, and they contain 75 mg per 2.6 oz, much less than what Erdman & MacDonald got. It’s possible that the amounts of calcium were downgraded in recent versions or that they got theirs from somewhere else. That’s for 1/2 cup cooked, which is a standard serving size, but I agree, it would be easy to eat 2-3 servings at a sitting, and much more if you really want to.
April 2nd, 2013 at 5:27 pm
Yes, but my question is about calcium absorbtion. Because calcium in other plant foods (such as beans, nuts and seeds) not well absorbed, I am worried that getting the remainder calcium (at least 450 mg in my case) only from these products may be not a good idea.
This is a sample menu that provide 450 mg of calcium:
2 navel oranges: 120 mg
1/4 cup dried figs: 40 mg
1/4 cup almonds: 95 mg
2 tbsp tahini: 40 mg
1 cup cooked navy beans: 125 mg
1 1/2 cup cooked brown rice: 30 mg
April 2nd, 2013 at 5:33 pm
dimqua,
I’d recommend eating some greens – they have lots of other benefits. It’s really hard to say if this is enough calcium – I would assume the vegans in the EPIC study, with higher calcium intakes and similar fracture rates to other diet groups, were, on average, eating some greens.
April 2nd, 2013 at 6:27 pm
Of course, I try to eat a lot of greens. Unfortunately, almost all greens available in our stores is not a good source of calcium. Broccoli and napa cabbage (pe-tsai) are probably the best sources that I can buy. Though, I grow a little bit of mustard greens in my house.
April 2nd, 2013 at 6:36 pm
dimqua,
I’m sorry to hear that. Eat as much broccoli as you can!
April 2nd, 2013 at 8:26 pm
Hi Jack,
Now that I look closer at the table in Erdman & MacDonald it has a footnote that says: “Adapted from Weaver et al. 1999” so it is pretty old info.
Looking at USDA SR25 sorted by Calcium per gram, the natural vegan food with the highest calcium per 100 grams I found is: “Spices; basil; dried”
with 2240mg calcium per 100g.
Slightly more feasible to eat a reasonable quantity of:
“Seeds, sesame seeds, whole, dried” 975mg calcium per 100g
The highest calcium density green would be:
“Stinging Nettles; blanched (Northern Plains Indians)” with 481mg calcium per 100g.
Skipping over some more greens probably you can’t find in your local market,
the highest calcium density common green would seem to be:
“Collards; frozen; chopped; cooked; boiled; drained; without salt” with 210mg calcium per 100g.
June 13th, 2013 at 4:12 pm
Dear Jack,
What do you think of this article?
We will really appreciate a rational follow up on this one:
http://www.drmcdougall.com/misc/2007nl/feb/whenfriendsask.htm
Thanks in advance
June 13th, 2013 at 4:17 pm
Joshua,
Here is my take on calcium:
http://veganhealth.org/articles/bones#fuss
September 5th, 2014 at 3:08 am
Dear Jack,
Is this true?
A recent study of Inuit (Eskimo) children found their diet, consisting largely of meat (which has almost no calcium), provided about 120 mg of calcium daily, but because of their physiologic adaptations these children were found to be healthy.4 As long ago as 1978 Paterson wrote in the Postgraduate Medical Journal, “Many official bodies give advice on desirable intakes of calcium but no clear evidence of a calcium deficiency disease in otherwise normal people has ever been given. In Western countries the usual calcium intake is of the order of 800-1000 mg/day; in many developing countries figures of 300-500 mg/day are found. There is no evidence that people with such a low intake have any problems with bones or teeth. It seems likely that normal people can adapt to have a normal calcium balance on calcium intakes as low as 150-200 mg/day and that this adaptation is sufficient even in pregnancy and lactation. Inappropriate concern about calcium intake may divert attention and resources from more important nutritional problems.”5 And that is exactly what the talented marketing people in the dairy industry have done with the help of friendly government officials in the USDA: they have placed the spotlight on the nutrient, calcium, which is easily obtained in sufficient amounts from almost any diet—and at the same time, taken the beam of truth off of the fat, cholesterol, and contamination—the life-threatening components of dairy foods. One of the ways this has been done is by sensationalizing rare cases of calcium deficiency in children on bizarre diets.
September 6th, 2014 at 6:27 pm
Joshua,
I don’t know about the studies on Eskimo children (did they cite it?), but I would disagree that 300-500 mg of calcium a day is enough for your average vegan living in the developed world.