A Popular Myth
The idea that spinach is a great source of iron has been instilled in many of us from a young age. The creators of the cartoon character "Popeye" chose spinach as the source for Popeye's power because of this nutritional myth. Popeye in turn helped instill this impression in every child who watched television in the early 1960's.
A German Study on Spinach Contained a Typo!
Spinach's high content of Iron was based on a 1870 German study that claimed spinach contained about as much iron as there is in red meat, which was totally inaccurate.
In reality, the result of the study was a simple typographical error. The scientists put the decimal point in the wrong place! It gave spinach 10 times more iron then any other green leafy vegetable.
It wasn't until 1937 when another group of German scientists discovered the mistake and realized that spinach has just 1/10th the level of iron previously claimed, about average for a green leafy vegetable. The level of iron was no longer so exceptional.
Spinach Also Has an Iron Absorption Inhibitor: oxalic acid
But spinach and iron were to have yet another falling out! In the early 1990s research refined what we know about iron absorption, and the amount of iron that was being absorbed into the body from spinach now became less than 10% of the actual amount found in spinach:
"Although much lauded as a nutritional vegetable, spinach has a drawback in that, while containing high levels of iron and calcium, the rate of absorption is almost nil. The oxalic acid binds calcium into an insoluble salt (calcium oxalate), which cannot be absorbed by the body. The same applies to the iron, as it is bound, leaving only 2-5% of the seemingly plentiful supply actually available for absorption."
The spinach iron myth had suffered two major blows. Iron levels were cut to 1/10th by a typographical error and then further cut to 2-5% of that 1/10th by oxalic acid. Spinach is rich source of vitamin A, vitamin E and several vital antioxidants, with more than a half-day’s supply of beta carotene found in just a half cup of the vegetable. Spinach is a healthy vegetable to eat for many reasons, but iron is not one them.
The myth about spinach and its high iron content was first propagated by Dr. E. von Wolf in 1870, because of the misplaced decimal point in his publication that led to an iron-content figure that was ten times too high. In 1937, German chemists reinvestigated this "miracle vegetable" and corrected the mistake. It was described by T.J. Hamblin in British Medical Journal, December 1981.
Ultimately, the bioavailability of iron is dependent on its absorption. This is influenced by a number of factors. Iron enters the body in two forms: nonheme iron and heme iron. All of the iron in grains and vegetables, and about three fifths of the iron in animal food sources (meats), is nonheme iron. The much smaller remaining portion from meats is heme iron (Williams, 1993).
The larger portion of dietary iron (nonheme) is absorbed slowly in its many food sources, including spinach. This absorption may vary widely depending on the presence of binders such as fiber or enhancers, such as vitamin C. Therefore, the body's absorption of non-heme iron can be improved by consuming foods that are rich in vitamin C. However, spinach contains high levels of oxalate. Oxalates bind to iron to form ferrous oxalate and remove iron from the body. Therefore, a diet high in oxalate (or phosphate or phytate) leads to a decrease in iron absorption.
Spinach also has a high calcium content. However, the oxalate content in spinach binds with calcium decreasing its absorption. By way of comparison, the body can absorb about half of the calcium present in broccoli, yet only around 5% of the calcium in spinach. Oxalate is one of a number of factors that can contribute to gout and kidney stones. Equally or more notable factors contributing to calcium stones are: genetic tendency, high intake of animal protein, excess calcium intake, excess vitamin D, prolonged immobility, hyperparathyroidism, renal tubular acidosis, and excess dietary fiber (Williams, 1993).
Spinach still has a large nutritional value, especially when fresh, steamed, or quickly boiled. It is a rich source of vitamin A, vitamin C, vitamin E, vitamin K, magnesium, and several vital antioxidants. Recently, opioid peptides called rubiscolins have also been found in spinach. It is a source of folic acid, and this vitamin was first purified from spinach. To benefit from the folate in spinach, it is better to steam it than to boil it. Boiling spinach for four minutes can halve the level of folate.
- Stanton, Rosemary. Complete Book of Food and Nutrition.
Vitamins, minerals & phytonutrients FAQ. Retrieved on 2007-06-14.
FAO spinach data sheet
- Cardwell, Glenn. Spinach is a Good Source of What?. The Skeptic. Volume 25, No 2, Winter 2005. Pp 31-33. ISSN 0726-9897
- Stanton, Rosemary. Complete Book of Food and Nutrition. Australia, Simon & Schuster, Revised Edition, 1995. ISBN 0-7318-0538-0
- The nutritional benefits of spinach were discussed in detail in the Skeptic magazine, (Winter 2005).
- T.J. Hamblin in British Medical Journal, December 1981.
- Williams, S.R. (1993) Nutrition and Diet Therapy 7th ed. Mosby: St. Loius, MO
Spinach. (2008, February 10). In Wikipedia, The Free Encyclopedia
. Retrieved 03:50, February 11, 2008, from http://en.wikipedia.org/w/index.php?title=Spinach&oldid=190398526
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|By: DrKuha on 2008/02/13 PM 7:34:40.
Yeah, but Spinach is delicious and has other vitamins.
|By: Anat on 2009/10/04 PM 9:04:33.
What's your point? No one said you shouldn't eat Spinach. And I don't think it's delicious whatsoever :x