Corn benefits: rich in lutein — but the clinical trial of lutein failed

Key benefits

1. 01Moderate evidence

   644 µg of lutein and zeaxanthin — but AREDS2's primary analysis failed

   Corn holds 644 µg of lutein plus zeaxanthin per 100 g, unmatched among grains. The pair deposit selectively in the macula and filter blue light.

   Here is the largest trial, stated plainly. AREDS2, published in JAMA in 2013, followed 4,203 people for five years, testing 10 mg of lutein plus 2 mg of zeaxanthin.

   Primary result: no significant reduction in progression to advanced macular degeneration (hazard ratio 0.90, 95 % CI 0.76–1.07, p = .12).

   The confidence interval crosses 1. No effect cannot be ruled out.

   Secondary analyses told a different story. Among the lowest fifth for dietary lutein intake, supplementation did appear to help. And a benefit appeared when lutein and zeaxanthin substituted for beta-carotene.

   Secondary analyses generate hypotheses; they do not prove them. Slice a trial into enough subgroups and some will come up significant by chance.

   Put together: adding more lutein to people already eating plenty did not help. For those eating little, the possibility remains open. Eating corn, kale and spinach speaks to the second case.

   One more thing. AREDS2 tested a supplement, not corn. Whether lutein from food behaves the same way is a separate question.

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2. 02Nutrition data

   The niacin is there but bound — the history of nixtamalisation

   Corn holds 1.77 mg of niacin (vitamin B3) per 100 g. As a number, that is respectable.

   But much of it exists as niacytin, a bound form the human digestive tract does not absorb.

   That fact changed history. When corn spread from the Americas to Europe and Africa, the cooking method did not travel with it. In Mesoamerica, corn had for millennia been simmered in limewater — nixtamalisation — and that alkaline process releases the bound niacin.

   In regions that adopted corn as a staple without it — southern Europe, the American South, parts of Africa, from the eighteenth to the twentieth century — pellagra became epidemic. It is niacin deficiency, running through dermatitis, diarrhoea and dementia to death. In the American South alone, an estimated three million cases and a hundred thousand deaths occurred over several decades in the early twentieth century.

   This rarely matters now. Diets built on corn alone are uncommon, and many countries fortify grain products with niacin.

   The principle still holds, though. There is a reason tortillas go through an alkaline treatment — and as long as corn is one food among many, none of this is a problem.

   Folate is 42 µg, 10 % of the adult requirement per 100 g; magnesium 37 mg; fibre 2 g.

3. 03Nutrition data

   Corn and corn products are different foods

   This may be the section that matters most.

   Food	kcal per 100 g	Note
   Boiled corn	86	what this page is about
   Popcorn (oil, salt)	around 500	bulky, so portions are small
   Cornflakes	360	many products add sugar
   Corn oil	884	100 g of fat
   High-fructose corn syrup	281	pure sugar

   Same crop, nutritionally different foods. The lutein and folate figures above apply only to the first row.

   High-fructose corn syrup in particular is a leading added sugar in processed drinks and foods, an entirely separate issue from the health of corn. Eating corn and drinking something sweetened with corn syrup are choices in opposite directions.

   Popcorn deserves a fair word. Strip out the oil, butter and salt and it is a whole-grain snack. Thirty grams of air-popped popcorn — a large bowl — is about 110 kcal with 3.6 g of fibre. What makes cinema popcorn what it is, is the oil and salt, not the corn.

How to eat it well

What to watch out for