I have been trying to increase my iron intake and was dismayed to learn that my frozen spinach only has 2% of my daily iron needs while fresh cooked spinach has about 20%. I have been under the impression that freezing vegetables preserves their nutrients from the moment they are picked/frozen and that transporting fresh vegetables across the country depletes the nutrients.

There was a whole about this some time ago either on TV or the internet or someplace.

So when I read the back of my frozen spinach container I was really surprised to find that it only has 2% of what I need.

Why is this? Is there a difference between the kinds of spinach that are grown for canning/fresh/frozen? Does freezing break something in the case of spinach? Does this happen with all fresh green leafy vegetables?

Thank you for your time.

  • 4
    If your goal is to increase iron intake, then spinach is actually a poor choice because while it contains quite a bit of iron, it's not in a form easily absorbed. Iron is much easier to absorb from animal sources (which is why vegetarians can have iron deficiency issues), but even from the plant-based sources, spinach is particularly bad because it contains other compounds which further inhibit absorption. See: en.wikipedia.org/wiki/…
    – Allison
    Commented Mar 23, 2011 at 23:23
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    @Allison: I think vegetarians with low iron counts just have poor diets. I have been vegan for many years, give blood regularly and have never had even the slightest of anaemia issues.
    – Orbling
    Commented Mar 24, 2011 at 1:45
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    @Orbling - I don't think your contention, about it just being poor dietary choices, conflicts with Allison's statement, at all. That seems to be her point, too - Spinach is actually a poor choice, for reasons stated. Her point was just that it's a bit easier to make the correct choice for non-vegetarians without as carefully evaluating the absorption. Commented Apr 13, 2017 at 18:30

3 Answers 3


Judging by the nutrition information I can easily find (for example, from nutritiondata.self.com), frozen spinach is generally cooked by boiling and draining. That's pretty much what I'd have guessed; it's certainly the easy way to cook things.

Unfortunately, that means that some nutrients are lost with the discarded water. I doubt it'd be different for any other green leafy vegetable - though it's certainly much harder to find frozen mustard greens!

The nutrition information for fresh spinach is for fresh, raw spinach; if you boiled and drained it, you'd make the same sacrifice that the frozen spinach has.

As for your generalization, freezing vegetables and fruits does preserve most things pretty well - but only what's actually left in them when they get frozen! And while transporting fresh vegetables around can cost you some "freshness", it's not going to affect minerals. Some vitamins could be lost by breaking down (I'm not an expert here, but it seems possible) since they're more complex molecules, but minerals are just single elements. Those iron atoms won't fall out of the spinach on the way, and they're certainly not going to be transmuted, either!

Edit: Essentially what's been said in the comments is that the USDA nutrition facts say that "Spinach, frozen, chopped or leaf, cooked, boiled, drained" has about half as much iron as "Spinach, cooked, boiled, drained". A discrepancy, indeed, though not the same one cited in the question. My interpretation here is that the frozen spinach is simply not cooked in the same way (boiled and drained more thoroughly) as the non-frozen.

An alternative, proposed by Adisak, is that the frozen spinach nutrition means that you've taken the already-cooked, frozen spinach and boiled it again and drained away even more nutrients. This seems unlikely; frozen spinach is already cooked, so there's no reason for the nutrition information to assume that you'll boil it over again. The description (it seems to me) is referring to the cooking that took place before it was frozen.

  • 1
    If you go to: nal.usda.gov/fnic/foodcomp/search and search for "spinach, frozen, cooked", choose any one of the amounts you get on the next page and see the iron content. Then search for "spinach, cooked" and choose the same amount you chose the first time, you might have the same, "huh" moment that I had.
    – user5396
    Commented Mar 23, 2011 at 18:49
  • I normally do not boil my spinach, but boiling is not the issue here. The idea that freezing vegetables will preserve nutrients was not my generalization. I can't look up where I heard it right now, but it is something that has been stated on health sites lately.
    – user5396
    Commented Mar 23, 2011 at 18:58
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    @Harriet: Boiling is the issue here. Freezing does preserve what's there, but if you boil the spinach and drain away the nutrients away with the water, freezing has nothing to preserve.
    – Cascabel
    Commented Mar 23, 2011 at 20:04
  • I am so sorry that we cannot communicate. I have been trying very hard to say that I am comparing boiled fresh spinach with boiled frozen spinach.
    – user5396
    Commented Mar 23, 2011 at 21:47
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    Freezing breaks down cell walls. If you then boil and drain frozen vegetables, you lose more nutrients than you do with fresh vegetables. The solution is to saute, steam, or even microwave frozen spinach so you are not boiling it and discarding most of the nutritional value in the liquid.
    – Adisak
    Commented Mar 23, 2011 at 22:38

Spinach is an okay source of iron as long as its not raw or boiled. Boiling, obviously, causes it to loose too many nutrients (I wouldn't boil any vegetable for that matter) and like stated above, the raw form is high in iron but not fully absorbable by the body. Fresh spinach, either lightly steamed or lightly sautéed is best. The same is true for other leafy greens, ie. kale and Swiss chard. Also, vitamin c will help your body absorb the iron from the spinach.

  • 1
    This all seems reasonable, but I don't think it really answers the question, which is about frozen spinach.
    – Cascabel
    Commented Jun 29, 2012 at 0:24

From Eating Well:

*Fresh Spinach vs. Frozen Spinach**
There’s a reason Popeye reached for a can of spinach rather than a fresh bunch. He knew that he could get more bang for his buck. You can squeeze a lot of spinach into a can or a box, delivering more spinach in less volume. (You would have to eat a mountain of fresh to get what you can in a 10-ounce box of frozen.) We prefer frozen spinach over canned—it’s got better flavor and is lower in sodium—but the same principle applies. One cup of frozen spinach has more than four times the amount of nutrients, such as fiber, folate, iron and calcium, than a cup of fresh spinach, so if you want to power up, do it with frozen spinach.

Winner: Frozen spinach!

  • 2
    If you compare by weight after cooking (i.e. you're comparing the same actual amount of spinach) fresh has more, as the question said. And you can indeed buy a bunch or two of spinach and cook it down to around the same amount as 10oz frozen.
    – Cascabel
    Commented Aug 13, 2013 at 0:36

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