Monday, October 11, 2010

Popeye didn't eat spinach for iron


Three generations of children have been told to eat their spinach so they get enough iron and grow up to be a strong as Popeye. Leaving aside the fact that muscle strength has got more to do with training and eating well, more than a focus on a single nutrient, we face those funny things called facts.

Spinach and iron

Spinach does contain iron. Half a cup of cooked spinach provides around 4 mg of iron. That’s pretty impressive considering the average bloke needs 8 mg a day and young ladies need 18 mg a day. Most other vegetables barely give you 1 mg of iron per half cup served. So, spinach has quite a bit of iron. And that’s about as far as some people look.

Although spinach is high in iron it is a lousy source of iron. How’s that? Well, it all revolves around the word “bio-availability”, that is, the ability of the body to absorb a nutrient from the intestines and use it within the body. Most of the iron in spinach is bound to oxalate (in the form of ferrous oxalate) and you do not have a digestive enzyme to split that binding to release the iron. That means that most, estimated at 95%, of the iron goes in one end and out the other about a day later. Spinach is iron’s way of taking a 10 metre (11 yd) voyage through your guts.

The decimal point fallacy

Now, Popeye is unlikely to have known that because he was created around 1929, featuring in his own cartoon in December 1930. A British Medical Journal paper from 1981 claimed that the fallacy of spinach being high in iron came about because the decimal point was placed in the wrong spot in the original analysis back in the 19th century, giving spinach an iron content ten times more than it was in reality.

Earlier this year, Dr Mike Sutton from Nottingham Trent University in the UK, refutes the whole argument stating that there is no evidence that a decimal point was ever placed in the wrong spot. He has even written to author of the BMJ article and says the response from the author provided no proof for the claim.

The really, really interesting bit

Well, to me at least. OK, so spinach is not a great source of iron and it never appeared to be. When Popeye was created in 1930 we knew about the minerals like iron and calcium and only the vitamins A, B1, C, D and E. Vitamins like folate, B12 and niacin were yet to be isolated.

Did Popeye himself say he ate spinach for iron? No. Not once, according to Mike Sutton. He did, on 3rd July 1932, mention that he ate spinach for one particular nutrient. Vitamin A (see cartoon). You and I know that there isn’t pure vitamin A in spinach; it’s in the pre-vitamin A form of beta-carotene. All the same, Popeye ate spinach for a vitamin, not a mineral.

What does it all mean?

It is wonderful when someone goes that extra distance to get information. So, hat’s off to Mike Sutton. I didn’t take Mike’s word for it. I went and bought the first two years of Popeye cartoons (because I yam what I yam), and I agree with Mike: Popeye only mentions vitamin A. Popeye is right, spinach is a great source of beta-carotene (and folate). Eat your spinach for the vitamins, not for the minerals.

If you would like to read the complete report by Mike Sutton then just got to: http://www5.in.tum.de/~huckle/Sutton_Spinach_Iron_and_Popeye_March_2010.pdf. Warning: it is a 35 page in-depth study as you might expect from a criminologist, which is just what Mike is.

Reference: British Medical Journal 1981; 283: 1671-1674

4 comments:

Mike Sutton said...

Hi Glen

I enjoyed reading your blog. Thank you for your kind words. What follows is in the spirit of healthy scepticism and informal academic debate, to take our knowledge about the impact of myths forward.

I read your (2005) paper published in the Skeptic, entitled “Spinach is a Good Source of What? Cartoon characters are not necessarily a good source of nutritional advice."

I wonder whether, in that paper, were you to some extent misled by the Spinach Popeye Iron Decimal Error Story (SPIDES) - as so many orthodox experts were?

As you found by - quite rightly checking the original sources for yourself rather than taking my word for it - Popeye was actually quite good at giving nutritional advice. As you write: spinach is an excellent source of pro vitamin A. That said, the latest research suggests it is harder to absorb even pro vitamin A from spinach than was thought earlier.

I think that some of the impact of the SPIDES on academic research in this area might possibly be revealed by the fact that Videlier and Piras (1990) in their paper “Health in strip cartoons” cover Popeye in just four words - simply to say that he smoked a pipe.

Perhaps another paper in the Skeptic is called for. By the way I have continued my research in the area and can demonstrate that there almost certainly was no decimal error. I’ve been reading turn of the century German and US papers on nutrition. Also the original SPIDES was started by another orthodox expert on nutrition earlier than Hamblin’s BMJ paper.

Would you be interested in writing a joint paper with me for the Skeptic Glenn. It would be the first time this latest research has been published.

Best wishes

Mike Sutton

Glenn Cardwell said...

Thanks Mike. Sorry about delayed response. Yes, the SPIDES sucked a lot in, including me. Love to be involved. Glenn

Mike Sutton said...

Hi Glenn

I am particularly interested in how and why certain myths may be more powerful than others. The SPIDES seems to be a particularly powerful myth. It drew me in also at first because I referred to it as though it were accurate 'authority' in a paper I presented at a conference.

Regarding the proposed paper, that's excellent. I'll email you today and we can work out how to best collaborate on the joint enterprise.

Mike

kv said...

Hello, Glen,

I arrived to your blog after reading a paper that actually cited Dr Sutton on the "SPIDES" affair:

http://m.sss.sagepub.com/content/44/4/638.full

I was looking up for some evidence about Popeye eating spinach for vitamin A, and in a google search this article's name got my attention.

I just wanted to point out that, despite this article remarking on the "decimal point fallacy", the figures presented actually have a decimal point error:

http://ndb.nal.usda.gov/ndb/foods/show/3214?qlookup=11457&max=25&man=&lfacet=&new=1

According to the source above, half a cup of spinach in fact contains 0.4mg of iron, not 4.

Kind regards,

Kadu Vido