On-Line Video of Vegan Nutrition: What Does the Science Say
Thanks to the Vegetarian Society of Hawaii, you can now watch a video of my talk Vegan Nutrition: What Does the Science Say on-line. Click here.
A special thank you to Dr. William Harris for filming and putting the video together!
December 27th, 2009 at 6:07 am
Jack;
Thank you ( and the Veg Soc Of Hawaii ) for posting this informative and interesting video.
As you can probably tell from my comments I am very interested if not a bit obsessed about osteoporosis.
In the talk, you had a slide that listed green leafy vegetables as having the same calcium absorbability as milk ( about 30%) and a slide that stated that eating 1.5 cups of cooked of leafy green vegetables should be enough to get 700 mg of calcium a day.
These numbers just don’t add up from other things I have read, even things not written by vegan health enthusiasts.
The revised edition of “Becoming Vegetarian” ( Davis, Messina page 103 ) lists most leafy green vegetables as having much greater calcium absorbability than cows milk. That chart ( and similar ones by sources that are not vegan enthusiastic ) also shows that most leafy greens will not provide 700 mg of calcium a day at just 1.5 cups cooked.
I was wondering if you know if these discrepancies are due to cutting edge research you have found or if there is a source of confusion somewhere.
Thanks much in advance for any information.
December 27th, 2009 at 2:07 pm
> and a slide that stated that eating 1.5 cups of cooked of leafy green vegetables should be enough to get 700 mg of calcium a day.
I did not mean to imply that you can get 700 mg of calcium from 3 servings of leafy greens. Rather, I was suggesting that eating 3 servings of leafy greens per day would increase you calcium enough that you would probably meet 700 mg. It really depends on what leafy green you choose. Collards, at 133 mg per 1/2 Cup would be an extra ~400 mg, while broccoli would only be an extra ~150 mg. I might want to discuss this in more detail in the future.
> you had a slide that listed green leafy vegetables as having the same calcium absorbability as milk ( about 30%)…The revised edition of “Becoming Vegetarian” ( Davis, Melina page 103 ) lists most leafy green vegetables as having much greater calcium absorbability than cow’s milk.
Well, it’s a little confusing. I have a paper that lists absorbability rates of calcium and it says that turnip greens, kale, mustard greens, and broccoli are absorbed at a rate of about 50-60%. It lists kale at 59%. However, another study found kale to be only 40%. This study showed soymilk to be 18-22%. I’ve seen research that puts supplements around 30%. And the papers linked to herein showed cow’s milk to be 22-32%.
The absorption rates can depend on how much calcium is ingested as calcium absorption tends to go down as calcium amounts go up.
This paper measured the overall calcium intake of people on a vegan diet to be 26%. In looking closer at that study, the subjects didn’t eat a lot of the leafy greens known to have a high absorbability; only broccoli was among their food choices.
I have also seen somewhere that collards have a high absorbability rate, but I can’t find that info right now.
Given all the above variables, I average it all out to be “about 30%”. I don’t think it makes a huge difference except that if you eat a lot of leafy greens (like well over 3 servings per day), you probably don’t need as much calcium. I’m skeptical that many vegans eat enough leafy greens to justify a lower calcium requirement and worry that if I emphasize the greater absorbability of calcium from leafy greens, vegans will think they don’t need as much calcium and so they won’t worry about calcium and they won’t eat many leafy greens.
Thanks for pointing both of these issues out. I’ve changed the slide to reflect the individual absorption rates.
December 27th, 2009 at 5:53 pm
I have also seen somewhere that collards have a high absorbability rate, but I can’t find that info right now.
If it is not an inconvenience I would be interested to see it. Collards are one of my favorite leafy greens and I was disappointed to learn last year that they have a high oxalic acid content. The only thing I could find online was an ancient USDA chart of oxalic acid in some common vegetables.
I’m skeptical that many vegans eat enough leafy greens to justify a lower calcium requirement and worry that if I emphasize the greater absorbability of calcium from leafy greens, vegans will think they don’t need as much calcium and so they won’t worry about calcium and they won’t eat many leafy greens.
I agree completely. I read an article years ago that showed that people do not eat as well or as little as they think they do. Even people who are educated about nutrition. My own estimates slide the longer I stay away from writing down what I eat.
I actually like green vegetables, make it a point to eat them and I still have trouble getting 2 cups a day on a consistent basis. Aside from digestive comfort there are the hassles of daily living, boredom with recipes and probably millions of years of evolution making me pick fatty, sweet things instead :).
January 10th, 2010 at 10:48 am
I did some research and while I did not find any studies measuring the calcium absorption rate for collards, they have a much lower oxalate content than spinach. Krause’s Food, Nutrition, & Diet Therapy textbook (2000) lists the following amount of oxalates per 100 g:
Spinach (boiled) 750 mg
Collards 74 mg
Kale 13 mg
So, collards are a lot closer to kale than spinach, both of which have been tested for calcium absorption rate.
January 21st, 2010 at 2:11 am
The easiest tastiest most healthful way to add huge amounts of greens to your diet is to have green smoothies – try it and you’ll find out how much greens you can disguise in a raw fruit smoothie – use whatever fresh fruit you have available plus add a banana or two to sweeten it up if it tastes a little bitter. During winter here in UK when berries are outrageously expensive and hard to obtain I use frozen berries , left to thaw so as not to strain the blender. The nicest tasting greens are spinach and romaine leaves, and as a sproutarian I always have alfalfa and red clover sprouts to add as well which are very mild tasting. Having been a 100% rawfood vegan for 5 years I, like many longterm rawfoodists, have reverted to eating lightly steamed greens like dark cabbage and kale as these tough greens don’t feel as if they are so easily digested raw.
January 21st, 2010 at 9:47 am
@Ruth Hawe
Spinach and romaine lettuce are poor sources of calcium.
Romaine lettuce just doesn’t have a lot of calcium for an amount you can reasonably eat, even blended into a smoothie. Much of the calcium in spinach is not absorbed because of high oxalic acid content.
The green leafy vegetables that have significant amounts of calcium tend to be harder to digest so I am wary of eating them raw, even chopped into itsy bitsy pieces by a blender. Even if they are digestible enough for personal comfort, taken raw I would be concerned with how much calcium I could absorb drinking them raw.
June 12th, 2010 at 4:54 pm
Beforewisdom:
My husband and I have been drinking green smoothies every morning for more than 18 months now. I am not a raw food enthusiast, but I still consume large amounts of raw fruits, vegetables, nuts and seeds. And I don’t remember having discomfort after drinking green smoothies. They don’t sit in your stomach very long and move on to travel through your digestive system fairly quickly. I haven’t seen anything that compared digestion of calcium from raw vs. cooked greens, but I would assume that we can get a similar amount (if not more) of calcium from raw greens blended into smoothies. And the main reason is that in smoothies greens have been reduced to pieces so small that we would not be able to achieve through regular chewing. And with green smoothies we can take up pretty much any greens, even those that are hardy like kale or collard greens and somewhat bitter like dandelion greens.
Jack:
I have heard a recommendation to drink fortified orange juice. But I don’t remember anyone highlighting calcium content of regular oranges. I looked up here (http://www.nutritiondata.com/facts/fruits-and-fruit-juices/1966/2) and found that one orange can have anywhere from 50 to 70 mg of calcium. And I often consume 3 to 5 of them a day, especially during the winter time when there is not a whole lot of other fruits around. Is there a reason why nobody recommends consuming oranges directly?
June 14th, 2010 at 6:28 pm
Lisa,
According to the USDA, a large orange has 70 mg of calcium. I guess people don’t bring this up much because it is a small amount compared to the 300 mg that is contained in a glass of cow or fortified soy milk. That said, if you eat 3 oranges or so a day, it can add up. But one cup of orange juice only contains 27 mg of calcium. I suppose, therefore, that the calcium must be in the pulp.