Article in Science / Chemistry / Biochemistry
Current USDA erroneous advice that spinach is a good source of iron may have its roots in a perverse paper published by the American Medical Association’s Council on Foods in 1937 - hereafter referred to as “The Spinach Paper.”
 
 
 

In the first Spin@ge article (Sutton 2011), I revealed how the United States Department of Agriculture (USDA) is irrationally promoting spinach as a good source of iron.This article provides some additional historical context for the USDA’s dissemination of harmful spuriofacts on spinach, iron and vitamin C.

Does current USDA erroneous advice that spinach is a good source of iron have roots in a perverse paper published by the American Medical Association’s Council on Foods in 1937 (hereafter referred to as “The Spinach Paper”)?

The Spinach Paper noted that improvements in biochemistry techniques had debunked earlier overestimates in the iron content of spinach. However, in 1937 science had not yet discovered that it was not a particularly good source of dietary beta-carotene, which the human body converts to vitamin A (Sutton 2011b). And so The Spinach Paper authors recommended that dried, frozen, fresh and canned spinach were all excellent sources of vitamin A. This is perfectly understandable, but I argue that what they concluded regarding the importance of spinach as a good dietary source of iron is not understandable at all.

In the teeth of conflicting evidence, contained even within The Spinach Paper, that spinach is not a good dietary source of iron, the US Council on Foods perversely concluded that it was.

The Spinach Paper noted how studies by Schlutz, Morse and Oldham (1933), and Stearns and Stinger (1937), with infants aged 9 to 54 weeks, found that a diet containing spinach had no significant impact upon infant iron retention. And the Council on Foods knew why; because by this time science had discovered that spinach contained significant quantities of the iron blocker oxalic acid. They wrote:

The evidence now is clear, however, that not all the iron in spinach is available to the organism. Tests for inorganic iron by the dipyridyl method have shown that only 20 per cent of the total iron is ionisable or “available” iron.” [1]

Given this finding one has to ask how they could have possibly written what came next in the paper:

“It may be concluded from these observations that, as far as its practical usefulness as a source of iron in the feeding of infants is concerned, spinach is of negligible value because little of it can be fed. However, even though all the iron of spinach may not be available, the total iron content is great enough for spinach to rate as a good source of iron for older children and adults. But direct experimental evidence is not now available to enable one to arrive at any conclusion regarding the precise value of spinach as a source of iron for persons beyond the age of infancy.”

If the incongruence has not already jumped out from this page, it helps to break things down.The first sentence makes perfect sense. My main concern is with the second sentence.

Today we know that nowhere near 20 percent of iron can be absorbed from eating spinach (see Sutton 2011), but what was known about that issue in 1937?

In 1937, 'knowledge' was that less than 20 percent of iron in spinach was available.

The authors of the Council on Foods paper knew that on average100g of fresh spinach contains a mere 0.5 percent dietary available iron. Which means that on the basis of Peterson and Elvehjem’s (1928) data, spinach has less than the 0.6mg of iron per 100g that was found in fresh tomatoes, less than 0.6 mg in red peppers, less than 0.7 mg in plums, and less than 0.6 mg in oranges. In fact, in 1937, even if as much as 20 percent of the iron in spinach could somehow be miraculously absorbed by a human being, knowledge at the time places spinach in the same unremarkable iron league as pears (0.46), lettuce heads (0.42) and gooseberries (0.47). A fact that could be further supported by research (Tisdall e.t al in 1937), which did find that cooked spinach, drained and ready to serve, contained no more available iron than canned tomatoes.

The choice of the words “may not” in the second sentence is peculiar, because the authors would have known from the research of the world leading University of Wisconsin scientists, reported two years earlier by science journalists in The Science News Letter (1935), that around 75-80 percent the iron in spinach “was” not available. And the use of the word “precise” in The Spinach Paper is also strange because, as the paper itself reported, fresh spinach – according to their knowledge at the time - contained on average 2.5 mg of iron per 100g, of which they thought they “knew” only some 20 percent was available.

Clearly then widely held expert knowledge at the time was that only some 19-25 per cent of iron from spinach was available. This means that it was known in 1937 that spinach is not a good source of iron when compared, for example, to the then “known” figures of 2.4 mg per 100g for turkey (Peterson and Elvehjem 1928) and 26 mg per 100g for beef liver[2] (Kohler, Elvehjem and Hart 1936). Yet, incredibly, the Council on Foods wrote in their conclusion of The Spinach Paper:

“Evidence regarding the amount of the iron of spinach that is available to older children and adults has not been reported at the present time.”

Accepting the fact that studies on babies at the time found the Wisconsin scientists were correct, while relying on the fact that no studies on older humans had at the time been undertaken, the Council on Foods perversely chose to claim that spinach remained a good source of iron for older children and adults.

In which case, and in light of all the most recent, orthodox and authoritative evidence available to them at the time - regarding what was then accepted 'knowledge' that at best only some 19 percent of the iron in spinach is available to anyone of any age (Kohler, Elvehjem and Hart 1935) - how could they possibly justify writing of spinach that:

“…the total iron content is great enough for spinach to rate as a good source of iron for older children and adults.”

Speculation and Conclusion

One might wonder whether perhaps external or internal organisational pressures forced the anonymous authors of The Spinach Report to protect spinach growers and the related food industry in 1937?

At the time The Spinach Report was published, the great depression of the late 1920’s was not a distant memory. In late 1935 through to 1936 things picked up. But in 1937 another economic depression hit the USA. . That same year, in the so called spinach capital of the world – Crystal City in Texas – the farmers erected a Popeye statue in honour of his creator E.C. Segar for his promotion of spinach – the fast food success behind Popeye’s strength.

We may never know what influenced the authors of The Spinach Report to write their seemingly irrational promotion of spinach as a good source of iron, but one possible reason is that they were in one way or another influenced by the economic plight of the spinach farmers. Quite why the USDA continues to claim, in the teeth of all the scientific evidence, that spinach is a good source of iron is an unsolved mystery. Perhaps the USDA is worried about the poor spinach farmers rather than the significant number of women in the USA, and elsewhere in the world who are low in iron and rely, along with their expert advisors, upon influential USDA advice for rational dietary choices? Or perhaps the continuing erroneous promotion of spinach is simply a coincidence and the USDA has just made an embarrassing mistake? Whatever the answer is, this most influential US government scientific department needs to get its facts straight.

And to end on that very theme, if you have read this far and you suspect that the real reason the USDA continues to this day to erroneously promote spinach as a good source of iron may have something to do with that most famous story of bad data impacting upon policy making, where a misplaced decimal point in 19th century analysis of the iron content of spinach exaggerated its iron content ten fold and influenced 20th century nutrition advice regarding spinach and iron, then I'm afraid you've been had. Because that entire story has been busted as a supermyth (See: Sutton 2010a; 2010b; 2010c).

References

Council on Foods (1937). Nutritional Value of Spinach. Journal of American Medical Association. Vol. 109. No. 23. p.1907-1909.

Kohler, G. Elvehjem, C. and Hart, E. 1936. Modifications of the Bibyridine Method for Available Iron. Journal of Biological Chemistry. Vol. 113. pp 49-53.

Peterson, W. H., and Elvehjem, C. A. (1928) The iron content of plant and animal foods. Journal of Biological Chemistry. Vol. 78. p. 215.

Schlutz, F. W. Morse, M. and Oldham, H. (1933). Influence of Vegetable Feeding upon Iron Metabolism of Infants. Journal of Pediat. 3: 225. July.

Sterns, G. and Stinger, D. (1937). Iron Retention in Infancy. Journal of Nutrition. 13. 127. February.

Sutton, M. (2011) SPIN@GE USA Beware of the Bull: The United States Department of Agriculture is Spreading Bull about Spinach, Iron and Vitamin C on the Internet. Bestthinking.com. Available online: http://www.bestthinking.com/articles/science/chemistry/biochemistry/spin-ge-usa-beware-of-the-bull-the-united-states-department-of-agriculture-is-spreading-bull-about-spinach-iron-and-vitamin-c-on-the-internet

Sutton, M. (2010a). Spinach, Iron and Popeye:Ironic lessons from biochemistry and history on the importance of healthy eating, healthy scepticism and adequate citation. Internet Journal of Criminology (Primary Research Paper series). http://www.internetjournalofcriminology.com/Sutton_Spinach_Iron_and_Popeye_March_2010.pdf

Sutton, M. (2010b) Discovery of Braced Myths. Supermyths blog. September 24th. Available online: http://super-myths.blogspot.com/search/label/Discovery%20of%20braced%20myths

Sutton, M. (2010c) The Spinach, Popeye, Iron, Decimal Error Myth is Finally Busted. Bestthnking.com .Available online: http://www.bestthinking.com/articles/science/chemistry/biochemistry/the-spinach-popeye-iron-decimal-error-myth-is-finally-busted

The Science News Letter. (1935). Spinach Over-Rated as Source of
Iron Vol. 28, No. 749. Aug. 17, p. 110

Tisdall, F.F. Drake, T.G.H. Summerfeldt, P. and Jackson, S. H. J (1937). The comparative value of spinach and tomatoes in the child’s diet. . Pediat. 11: 347.


[1] See Kohler et al (1936)

[2] Of which, 69 percent was “known” to be available.

 

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