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Archive for the ‘oxalates’ Category
As you’ve discussed in previous posts, phosphoric acid, caffeine, and sodium inhibit calcium absorption and/or promote calcium excretion.
Guidelines state that the body can only utilize 500 mg of calcium at a time.
That said, would extra calcium (beyond 500 mg) at a meal blunt the detrimental effects of phosphorus, caffeine, and sodium that are consumed concurrently?
– Megan Smith
In theory, yes, extra calcium would blunt the effects of the components you mention.
Semantics is key here. The body can utilize 500 milligrams of absorbable calcium.
A cup of cooked spinach, for example, contains 245 milligrams of calcium. Due to spinach’s high oxalic acid content, only five percent of that calcium (12 milligrams) are absorbed.
Hence, someone would need to eat 41 cups of spinach (10,045 milligrams of its calcium) to get 500 milligrams of absorbable calcium.
So, technically speaking, extra calcium does blunt the effects. However, once the body absorbs 500 “true” milligrams of calcium, extra milligrams become irrelevant.
I have come across conflicting information on sesame seeds as a good source of calcium.
Some websites (none written by nutritionists) claim they are, others claim they are not. A few vegan websites I’ve been to [refer to] them as “calcium superstar” or a “calcium powerhouse”.
So, do you get calcium from these tasty seeds or not?
– Evan Raggio
You do, but not as much as some uninformed individuals may lead you to believe.
Describing sesame seeds as a “calcium powerhouse” is incorrect. In the non-dairy world, that superlative is better suited to kale and mustard greens.
There are two important factors to keep in mind about calcium and sesame seeds.
Number one: unhulled sesame seeds (ones which contain the hull) contain more calcium than hulled sesame seeds (ones without the hull).
Whereas one tablespoon of unhulled sesame seeds delivers nine percent of the Daily Value of calcium, that same amount of hulled sesame seeds delivers four percent.
You may think, “alright, so I’ll just eat unhulled sesame seeds, and make tahini from them as well!”
Here’s the other issue — unhulled sesame seeds contain a large amount of oxalates.
Oxalates severely restrict calcium absorption. Spinach is also very high in oxalates, which is why it is not a good source of calcium (I am flabbergasted by the amount of articles I have seen written by Registered Dietitians which tout spinach as an “excellent source of calcium” — it is NOT!).
So, while you do get some calcium from sesame seeds, they are certainly not a powerhouse or an “excellent source”.
“Spinach is full of pleasant surprises [and a top-ten "power food"]. It’s a natural source of iron… and a rich non-dairy source of calcium.“
Those sentences appear in The Sonoma Diet, penned by Registered Dietitian Connie Guttersen.
I find it incomprehensible that a Registered Dietitian can make such an elementary mistake.
Although spinach offers plenty of vitamins, antioxidants, and phytonutrients, it is not a rich source of iron or calcium.
Unlike other leafy greens (i.e.: bok choy, broccoli, mustard greens, and kale) which are very good sources of both those minerals, spinach is loaded with compouds known as oxalates.
Oxalates bind to iron and calcium, significantly decreasing absorption of those minerals in our digestive systems.
Consider the following:
- A half cup of cooked Chinese cabbage delivers as much calcium as a cup of milk
- One and a quarter cups of cooked bok choy deliver as much calcium as a cup of milk
- Eight cups of cooked spinach deliver as much calcium as a cup of milk
What makes this tricky is that the figures presented for spinach in terms of iron and calcium content do not take into account decreased absorption. Therefore, you will see that a half cup of cooked spinach “provides” 115 milligrams of calcium (11% of the Daily Value). Sadly, we only absorb 10 to 15% of that amount.
Please share this tidbit with as many people as you can. I am continually amazed by the amount of health professionals (dietitians, doctors, and educators) who keep this myth alive.
The range of confusion varies from those who think dairy products contain the most absorbable type of this mineral to people who think spinach is a great source of calcium.
Let’s clarify these points.
Are dairy products a good source of calcium? Yes. After all, eight ounces of milk provide a third of the daily value of calcium.
Are dairy products the only way to get calcium? Absolutely not.
Do dairy products provide calcium with the highest bioavailability? No.
Consider the following:
Eight ounces (one cup) of milk contain 300 milligrams of calcium.
A half cup of cooked bok choy provides 79 milligrams of calcium.
To someone unfamiliar with nutrition, the conclusion might seem obvious: “I need two cups of bok choy to get as much calcium as a cup of milk!”
Alas, nutrition science isn’t always as obvious as it seems.
You actually only need one and a quarter cups of cooked bok choy to match the calcium you would get from a cup of milk since the calcium in bok choy is more absorbable than the one in dairy products.
The same thing happens with Chinese cabbage. A half cup of this cooked vegetable offers 239 milligrams of calcium, but that equals the amount of absorbable calcium in a cup of milk.
Let’s now turn our attention to spinach. I am continually amazed by the amount of self-touted (though, clearly, not really) nutritione experts who list this vegetable as a good source of calcium.
A half cup of cooked spinach offers 115 milligrams of calcium. However, due to its high amount of oxalates (organic acids naturally found in spinach that inhibit calcium absorption), it takes EIGHT cups of cooked spinach to equal the amount of absorbable calcium in one cup of milk.
It just so happens that unlike spinach, the Brassica family of plants — including broccoli, kale, bok choy, cabbage, and mustard greens) does not accumulate oxalate, thereby providing highly absorbable calcium.
I know some people like their nutrition advice in absolute form (“NEVER eat this, ALWAYS eat this), it’s not my style.
My suggestions provide you with plenty of choices. If you like milk, drink it — it provides a significant amount of calcium.
If you don’t like it or don’t want to include it in your diet, no need to worry about calcium as long as you include greens from the Brassica family and other non-dairy sources (tofu, tempeh, almonds, calcium-fortified alternative milks, etc.) in your diet.
I have heard, though, that cooking spinach will decrease the amount of oxalates.
Is this rumor true?
– Christine (last name unknown)
Via the blog
The rumor is true, but irrelevant.
Yes, boiling reduces oxalate levels in food. However, this reduction is minimal, and it also leeches out vital water-soluble nutrients.
By the way, oxalates also bind the calcium in spinach, so if you’re looking to get that mineral from a green vegetable, broccoli is a smarter bet.
I would like to know the best way to incorporate calcium [in]to my diet.
– Maria Barbosa
Before I answer your specific question, let’s briefly discuss the larger issue.
Osteoporosis — a condition in which bone tissue deteriorates and bone density decreases, thereby weakening the skeletal system (see accompanying illustration) — is especially prevalent among women.
In the United States alone, it is estimated that approximately 10 million adults currently live with osteoporosis, and an astounding 75 percent of them are women.
In case you are wondering about the difference between these two groups, a decline in estrogen at menopause is associated with decreased bone density.
Men, meanwhile, are protected by testosterone. Although testosterone levels decrease with age, they are still at a sufficient range to guard against the onset of osteoporosis.
Since osteoporosis is “symptom free” (you don’t feel weak, bloated, tired, or get headaches), it is completely feasible to develop it and be completely unaware of this for years.
To discuss how osteoporosis starts – and how to make the necessary changes once diagnosed with it – let’s go back to the beginning.
Our bones are a vast storage unit for a handful of minerals, especially calcium.
It’s important to have a strong reserve of calcium because we lose it on a daily basis.
All bodily excretions (sweat, urine, and feces) contain calcium, and our nails require it for production and growth.
Calcium is also needed for a variety of bodily functions (i.e.: forming blood clots).
Consume adequate amounts of this mineral every day and you easily replenish any losses.
If calcium intake is insufficient, that’s where the problem begins.
The body, desperate for calcium, doesn’t find any circulating in the blood and goes to the trusted storage unit for some.
In turn, bones are demineralized and broken down.
Imagine this happening on a daily basis for ten, twenty, even thirty years!
By the time you hit the fifty or sixty year-old mark, your bones are — not surprisingly — quite fragile and acutely demineralized.
Although many people automatically equate osteoporosis with calcium, there are other factors to keep in mind.
A crucial one is Vitamin D, which helps our bodies absorb calcium (this is why you often see calcium supplements also containing Vitamin D).
As I have explained before, Vitamin D is not found in many foods (the best source is actually the sun).
If you live in an area of the world that does not receive much sunlight for five or so months of the year, or if your dermatologist has strongly recommended you always use UV-proof skin lotions, you run the risk of being significantly deficient.
The solution? Reach for a daily supplement! Aim for 1,000 International Units a day.
Protein also plays a role in preventing osteoporosis.
Both sides of the spectrum – not getting enough or getting too much – are problematic.
A lack of protein in the diet will hinder the body’s ability to repair and rebuild bone tissue.
An excess, meanwhile, results in urine outputs with higher calcium levels than normal.
Phosphoric acid is also worth paying attention to. Found in regular and diet sodas, it disturbs the body’s calcium balance mechanism, often resulting in calcium being leeched from bones.
Sodium – a mineral the majority of people in the United States overconsume– also plays a role in osteoporosis.
High sodium intakes increase calcium losses through the urine (a result of the body attempting to keep various mineral levels proportional).
With all that in mind, how can you be proactive about lowering your risk of developing osteoporisis (and maintaing what bone mass you do have at the time you are diagnosed with it)?
From a nutritional standpoint, make sure you get sufficient amounts of calcium and Vitamin D and that you do not surpass maximum recommendations for sodium and protein.
Aim for 800 – 1,200 milligrams of calcium a day.
To answer your question, all dairy products are a great source, as are tofu, almonds, oats, and any fortified products.
Spinach, however, is one food that gets way too much credit.
Although it offers substantial amounts of various nutrients, don’t put it in your osteoporosis defense kit.
Spinach offers significant amounts of calcium, but also contains high levels of oxalate, a compound that binds to calcium and greatly reduces its absorbability in our gastrointestinal tract.
The good news is that oxalates only affect calcium absorption of the food they are in.
So, if you’re having a spinach and tofu stirfry, only the dark leafy green vegetable’s calcium will be practically rendered useless.
Aside from nutrition, one of the best things you can do to minimize your risk of developing osteoporosis (and prevent further bone demineralization if you have already been diagnosed) is weight-bearing exercises.
This does not mean you need to necessarily start lifting heavy weights or buildmuscles. It’s really just about performing physical activity in which the muscles have to resist weight.
Remember, bone strengthens up when stressed. Hence, challenging it with weights on a regular basis helps to maintain — and even increase — its density.
As you can see, there are helpful steps you can take at any stage of the game. There is no reason to give in to osteoporosis.
– Micah and Katie
(Via the blog)
Let’s start with a few basics.
Iron is located in hemoglobin, a protein within our red blood cells (pictured at left).
Hemoglobin is responsible for delivering oxygen from the lungs to various body tissues so other cells – which rely on oxygen — can use it.
Low hemoglobin levels are therefore problematic, as they result in cells not having enough oxygen delivered to them to perform their required tasks.
The recommended dietary allowance for iron is set at 8 milligrams for men and women over 50, but vegetarian men of all ages and women over 50 should be consuming approximately 15 milligrams a day.
The reason? There are two types of iron – heme and non-heme.
Heme is found in animal sources of iron, non-heme in vegetarian contributors.
Non-heme iron is not absorbed as easily, so 10 milligrams of purely non-heme iron is not sufficient.
This is not to say that vegetarian diets are inadequate; simply that they require a higher intake of iron.
This is not too difficult to do, especially given the high amount of fortified vegetarian products that provide plenty of iron.
Beans and dried fruits are also great sources of this mineral.
Keep in mind that women who menstruate have higher iron needs.
Those on omnivore diets are recommended to consume 18 milligrams a day. Vegetarian women falling into this category should be taking in 30 to 35 milligrams a day.
The issue of low iron stores is an interesting one because it often gets mixed up with iron-deficiency anemia, although they are two very different things.
Iron stores run a gamut, from “inadequate” to “excessive”.
In the middle of that spectrum lies the “adequate/healthy” point.
Anemia is actually the “end stage”, or lowest point, of iron deficiency.
The condition of anemia is diagnosed by looking at hemoglobin, mentioned above, and hematocrit (the number and size of red blood cells).
In anemia, there simply isn’t enough iron present to form hemoglobin. In turn, cells are not receiving enough oxygen.
Now here’s where things get interesting.
Someone falling in between adequate stores and anemia has what is known as “iron deficiency.”
Iron deficiency is diagnosed by looking at levels of the transferrin – a protein that binds to and transports iron – receptor and transferrin saturation (in other words, the percentage of molecules of transferrin that are saturated with iron).
The bad news is that standard blood tests only show hemoglobin and hematocrit.
Hence, you could very well be iron deficient and not know it.
You need to specifically ask for transferrin receptor and transferrin saturation blood labs.
This is crucial because iron deficiency affects brain function, particularly short-term memory, concentration, and cognitive processes.
What is important to know is that iron deficiency has nothing to do with the type of iron you are consuming.
If anyone tells you you need to eat meat to increase your iron stores, feel confident to tell them to read the literature.
The solution to increasing iron reserves is simply to consume more iron.
In the case of soy ground beef, two ounces contain 2 milligrams of non-heme iron. That same amount of ground beef contains approximately 1.6 milligrams of the heme variety.
Another interesting tidbit: runners — especially vegetarian ones — need even MORE iron.
When we exercise, we undergo a miniscule amount of internal bleeding (which is normal), thereby increasing blood loss — and our chances of developing anemia if we are already iron deficient.
Again, what is important thing to keep in mind is that increasing body stores can be done with animal or vegetarian sources as long as the right amounts are being consumed.
There are also certain food combinations worth keeping in mind.
Vitamin C helps with absorption of non-heme iron.
So, a soy-based meal accompanied by a tomato salad or glass of orange juice will be beneficial.
There are also some components of food that will have the reverse effect and inhibit the body’s ability to absorb non-heme iron.
These include oxalates (found in spinach, quinoa, collard greens, peanuts, and strawberries), tannins (found in tea and coffee) and, more strongly, phytates (found in whole grains).
Therefore, a soy patty in a whole wheat bun with a side of spinach salad isn’t the most efficient way to include more iron in your diet.
Here’s some good news, though. Since sprouted whole grains have lower levels of phytates, you’re better off enjoying Ezekiel 4:9 bread products than standard whole wheat varieties.
Many, many thanks to Dr. Domingo Piñero of New York University’s Department of Nutrition, Food Studies, and Public Health for providing a private iron 101 mini-lesson earlier today to help me answer this question as exhaustively — and accurately — as possible.