Thursday, December 23, 2010

Spinach - I was right for the wrong reason

Twenty-nine years ago I wrote an article in the British Medical Journal about scientific fraud, fakes and medical mistakes in which I revealed that spinach is not a good source of iron. I further revealed that a German Chemist made a mistake by misplacing the decimal point. Here's what I wrote:

In the year that Popeye became once again a major movie star it
is salutary to recall that his claims for spinach are spurious.
Popeye's superhuman strength for deeds of derring-do comes
from consuming a can of the stuff. The discovery that spinach
was as valuable a source of iron as red meat was made in the
1890s, and it proved a useful propaganda weapon for the meatless
days of the second world war. A statue of Popeye in Crystal
City, Texas, commemorates the fact that single-handedly he
raised the consumption of spinach by 33%. America was "strong
to finish 'cos they ate their spinach" and duly defeated the Hun.
Unfortunately, the propaganda was fraudulent; German
chemists reinvestigating the iron content of spinach had shown
in the 1930s that the original workers had put the decimal point
in the wrong place and made a tenfold overestimate of its value.
Spinach is no better for you than cabbage, Brussels sprouts, or
broccoli. For a source of iron Popeye would have been better off
chewing the cans.

I was never quite sure where I got that information. At the time I was making a reputation as an author of humorous articles for the popular magazine World Medicine. I was also interested in scientific fraud and was asked to write an article on it for the Christmas edition of the BMJ by the then editor, Stephen Lock. It was to be a light hearted article without the usual scrupulous references that I would normally supply for a journal like the BMJ. Given that I was debunking a number of frauds that included examples of plagiarism, I was uncomfortable with this suggestion and we agreed that I should provide a bibliography at the end. This is what I wrote:

Having spent so much of my time talking about people whose work
was unoriginal, I should mention that little of my article is based on
original work but has been derived from the publications of others.
Among these I should particularly like to mention:
Arther Koestler: Case of the Midwife Toad. London, Hutchinson.
Malcolm Bowden: Ape Men-Fact or Fallacy. Bromley, Sovereign
William J Broad: Science 208:1438-40,209:249,210:38-41, 171-3.
Colin Tudge: World Medicine 1974 Jul 17:34.
Leon Kamin: New Society 1976 Dec 2:460-1.
Marjorie Sun: Science 1981 ;212:1366-7.
D D Dorfman: Science 1978;201:1177-88.
Ian St James Roberts: New Scientist 1976 Nov 25:466-7.
C Joyce: New Scientist 1981 Apr 9:68-9.
D Dickson: Nature 1981 ;289:227.
Nature 1980;286:433, 831-2.
Lancet 1976;ii: 1066-7.
British Medical Journal 1980 ;281 :41-2.

I have rechecked these references but none of them refer to Popeye. When people have asked me about it (including the late, great, Martin Gardiner) I have always replied that I thought I remembered reading it in Reader's Digest but I have never been able to find the article.

Now some fascinating research by Mike Sutton has found out the whole truth behind the decimal point and the iron in spinach myth and I am pleased to be able to say that I was right about spinach being useless as a source of iron, but utterly wrong about why the myth has taken hold.

Dr Mike Sutton is the originator of the Market Reduction Approach to theft. He is the General Editor of the Internet Journal of Criminology and is Reader in Criminology at Nottingham Trent University in England. He is an alumnus (BA hons. Law and PhD) of the University of Central Lancashire.

In an earlier article Dr Sutton accused me of inventing the story. I knew that to be untrue, but I couldn't remember where I had read it. I still don't remember, but I now know where the information came from although I'm sure it wasn't in the Spectator that I read it in as Dr Sutton implies. Some other author must have picked it up from the Spectator and written it down elsewhere for me to pick up.

It appears that the original published source of this story was nutritionist, Arnold E. Bender. He first mentioned it in his inaugural professorial lecture in 1972 and later in an article in the Spectator where he claimed, according to Sutton, that "a German textbook on nutrition (Noorden and Salomon 1920; 476) replicated an earlier decimal point data mistake made by generations of textbooks that unquestioningly replicated erroneous data first published in 1870 by the German scientist E. von Wolff":

“For a hundred years or more spinach has been (and clearly still is) renowned for its high iron content compared with that of other vegetables, but to the joy of those who dislike the stuff this is quite untrue. In 1870 Dr E. von Wolff published the analyses of a number of foods, including spinach which was shown to be exceptionally rich in iron. The figures were repeated in succeeding generations of textbooks – after all one does not always verify the findings of others – including the ‘Handbook of Food Sciences’ (Hundbuch der Ernahrungslehre) by von Noorden and Saloman (sic) [1] 1920.

In 1937 Professor Schupan eventually repeated the analyses of spinach and found that it contained no more iron than did any other leafy vegetable, only one-tenth of the amount previously reported. The fame of spinach appears to have been based on a misplaced decimal point.”

My article in the BMJ has been the spur to countless other articles perpetuating the decimal point myth. So what is the truth? You can read it for yourself if you click the link, but for those who don't have the time, it does seem that Emil von Wolff did over estimate the amount of iron in spinach. In 1871 he reported that fresh spinach contained 3350mg of iron per 100g. This is from Professor Bender's article in the Spectator:

One common belief, that spinach is good for you, appears to be due to experimental error since the belief predates the Hollywood nutrition films based on the muscular development of the film star Popeye. I am indebted to Professor den Hartog of Holland for tracing the possible origin of this belief. It appears to date soon after 1870 when Dr E. von Wolff published food analysis showing spinach to be exceptionally rich in iron, a figure that was repeated in many generations of textbooks; it was in the Handbook of Food Sciences (Handbuch der Ernahrungslehre) by von Noorden and Saloman in 1920. In 1937 Professor Schupan analysed spinach for its iron content with µ-µ’-dipyridyl and found the figure to be one tenth of that reported by von Wolff – the fame of spinach may well have grown from a misplaced decimal point.”

There seems no published work of Professor den Hartog that makes this claim and Sutton concludes that the information may have been conveyed in informal conversation.

Quoting Sutton: "Noorden and Salomon’s (1920 Handbuch Der Ernährungslehre Erster Band Allgemeine Diätetik. Berlin. Verlag Von Julious Springer.) figure for the amount of iron in dried spinach is 445 mg of iron per 100g. This figure is derived from Haensel, who presented the iron content of spinach in percentage terms as 0.445 per cent. To convert this figure to mg per 100g it is simply multiplied by 1000 - which is 445.

Professor Bender was completely wrong about the source of Noorden and Salomon’s data on the iron content of spinach. Absolutely none of it came from von Wolff. Not one single figure. The figure Bender thinks came from the work of Wolff in the 1870’s in fact came from Haensel (Haensel, von. E. (1909) uber den eisen- und phosphorgehalt unserer Vegetabilien. Biochem. Zeitschr 16. 9."

Sutton believes that "The source of Bender’s decimal error belief derives from the fact that accepted knowledge at the time when Bender was writing quite correctly held that dried spinach contained 44.8 mg of iron per 100g (e.g. Jackson 1938Determination of Iron in Biological Material. Industrial & Engineering Chemistry Analytical Edition. 10 (6), 302-304). Subsequent research has recorded a figure of 44.6 (Rewashdeh et al 2009 Iron Bioavailabilty of Rats Fed Liver, Lentil, Spinach and other Mixtures. Pakistan Journal of Biological Sciences. 12 (4) 367-372.) From this it is easy to see where the decimal error idea in Bender’s spinach story came from. Had Haensel (1909) moved his decimal point to give a figure of 0.0445 per cent iron he would have had an accurate figure for the amount of iron in dried spinach of 44.5 mg per 100g."

It is clear that von Woolf's result cannot be corrected by simply moving the decimal point one place - his result is at least 50 times too great. It is far more likely that the method that he employed was faulty and Sutton has discovered that other measurement made during this period was similarly awry. Certainly there has been confusion between the amount of iron in fresh spinach and dried spinach and the water content of spinach depends on how recently it was picked, nevertheless, even by the turn of the twentieth century errors in earlier measurements were readily apparent without the need to invoke decimal places.

In fact most foodstuffs whether green vegetables or meat have similar amounts of iron; what matters is whether the iron is available for absorption by the human gut. Whereas the iron in meat is readily available this is not true for green vegetables. Whatever the result of measurements of iron, you cannot prevent or cure iron deficiency by eating spinach. Meat, red or white, (but not from shellfish) is what you need.

The moral of this story is that a good story is not necessarily a true story.

1 comment:

George Watkins said...

I see Sutton has taken things a step further and is now mythbusting the USDA to "stop spreading bullshit" (what a great line) about spinach and iron.

Check it out:

By the way it is good to see that you and Sutton on the other Bestthinking article comments spar like true gentlemen. So rare these days. I take my hat off to you sir.