The health department, WIC offices, and even natural health care practitioners often suggest spinach (among other things) as an excellent source of iron.  And it may be a better source of iron than many other foods.  (Not all foods have any iron!)  But it isn’t nearly as good a source of iron as we’ve been led to believe, for several reasons.

Usability Matters!

First, just as it isn’t true that “a calorie is a calorie” (the body uses different types of calories differently), it isn’t true that “iron is iron.”  (The same is the case for most, if not all, other nutrients, as well.)  Different forms of certain nutrients are absorbed more or less readily by the body.  Most nutritionists either aren’t aware of this or choose to ignore it, but it can make a huge difference!

Where iron is concerned, there are two major forms: “heme” iron (blood-based iron, or that which comes from animal flesh) and non-heme iron.  The vegetarians may not like this, but “heme” iron is far more readily absorbed by the body than non-heme iron.  According to the only source I could find with actual numbers, non-heme iron is absorbed at a rate of about 2-20%, while heme iron is absorbed at a rate of about 15-35%.

Application #1: A vegetarian diet is not the same as an omnivorous one.  It does take more effort to ensure adequate intake of certain nutrients on a vegetarian diet.  (And don’t even get me started on vegan diets.)

Anti-Nutrients

Back to spinach.  Not only does spinach, as a plant food, contain non-heme iron, rather than heme iron, it also contains oxalates.  Oxalates, like certain other elements such as phytates, are considered “anti-nutrients,” because they block the body’s ability to absorb certain other nutrients (typically minerals).

The phytate debate is big in the whole-grain community, because it is claimed that phytates in whole grains make them unhealthy.  Personally, I believe that it is by design that we get more nutrients from certain foods and less from others, and that we get more or less depending on food preparation method – this causes greater variety in our nutrient intake!

But regardless of the ultimate overall conclusion, it is unquestionably the case that the high oxalate content in spinach greatly decreases the absorbability (is that a word?) of the iron it contains.  (Side note: spinach isn’t a good source of calcium, either, for similar reasons.)

Total Content

Finally, spinach only contains so much iron in the first place.  So once we account for the previous two factors, there’s little left for actual use by the body.  According to the USDA’s nutrient database, an entire 10-ounce package of spinach contains only 7.7 mg of iron.  Most people (especially those having to be encouraged to eat spinach) probably don’t eat a whole package at a time, though.

A cup of spinach is probably a more practical serving size.  According to the same source, a cup of spinach contains only .81 mg of iron.  For purposes of comparison, a cup of Breyer’s chocolate ice cream contains about 1.43 mg.  (According to the percentages on the package’s nutrition label, converted to mg based on the information from a multivitamin package.)  I’m not trying to say that chocolate ice cream is nutritionally superior to spinach!  Just trying to put the iron content into perspective.

Putting All the Pieces Together

So let’s assume you’re eating that 1 cup of spinach.  You’re technically taking in .81 mg. of iron.  If we assume that the iron is absorbed at the highest rate for non-heme iron, you’d be actually getting, for practical purposes, about .13 mg.

But it’s highly unlikely that anyone would absorb it at the highest rate.  For one thing, it’s less-than-perfect simply because our bodies aren’t in perfect health (and, again, that’s even more likely to be the case if you’re having to be encouraged to eat nutrient-dense foods).  But then we have to account for the oxalates.  To be generous, let’s assume that the oxalates allow for absorbing the iron at about a halfway rate (midway between the 2% and 20%).  I suspect it’s actually closer to the bottom, but we’ll go with the midway point, which is 11%.  That’s less than .09 mg of iron in that same cup of spinach, when you count how much your body is actually gaining for use!  (In case anyone was curious and doesn’t care to do the math, at the 2% rate, it would be less than .02 mg.  Spinach does contain some vitamin C, which aids in iron absorption, so that’s a good thing.)

Application #2: Although spinach is a healthy food, with lots of other nutrients – most notably vitamin K, which is also excellent for blood-building – it’s probably not an amazing source of dietary iron.  Meat – especially red meat – is better.  (A 1/4 lb. serving of ground beef [95% lean] yields 2.45 mg of heme iron, for a minimum of .36 mg actually used by the body.)

Also note that the absorption of heme iron remains rather steady, unaffected by what you eat (or don’t eat) with it.  The absorption of non-heme iron can be improved by eating it together with heme iron (and/or vitamin C).

Application #3: Adding a little bacon (the real stuff, not imitation “bits”) or other chopped meat to your salad will help your body utilize the iron in the spinach more effectively.

Disclaimer: I am not a health professional, just a mom with an interest in whole food-based nutrition.  Please do your own due diligence and use your own common sense when making any dietary choices for yourself or your family.  This post should not be construed as medical advice, and is not intended to diagnose or treat any illness.

This post is being shared at Natural Living Monday, Fat Tuesday, Tuesday Greens, Titus 2 Tuesday, Wednesday Fresh Foods, Real Food Wednesday, Whole Foods Wednesday.