by Marion Nestle
Mar 13 2010

The fate of vitamins in vegetables, stored and cooked

Nothing about nutrition is simple.

I was intrigued by the Observatory column in the New York Times last week.  USDA researchers showed that supermarket spinach stored under continuous fluorescent light retained more vitamins than spinach stored in the dark for at least 9 days.  Their hypothesis: the light promotes continued photosynthesis and protects against degradation.

I was curious to know whether they measured vitamin C.  I checked the article in the Journal of Agricultural and Food Chemistry (February 2010, DOI: 10.1021/jf903596v).  Indeed they did.  This seems odd because this vitamin is well known to be degraded by light.  That is why orange juice is usually stored in opaque containers.  One explanation might be that orange juice is stored a lot longer than 9 days.

Cooking also destroys vitamin C.  While I was looking for that article I came across this one, which describes experiments looking at the effects of common cooking practices (boiling, microwaving, and steaming) on beneficial antioxidants and phytochemicals in Brussels sprouts.

Steaming increased phytochemicals in fresh and frozen sprouts.  Boiling did too, but only in the fresh vegetables.  Cooking reduced phytochemical content in frozen samples.  Microwaving was the best cooking method for retaining color and vitamin activity.  As expected, all cooking methods destroyed vitamin C.

So what to make of this?  Eat a mixture of cooked and uncooked vegetables and the vitamins will take care of themselves.  If you do cook, steaming is great and microwaving is better for preserving vitamin activity.  For vitamin C, raw wins every time.

Happy weekend!

  • Anthro

    Thank you for this clear and concise information. This is an area where myth abounds and the clarification is most welcome.

    I used to think I had to eat all my veggies raw, but some of them just don’t agree with me when eaten raw–and who likes raw brussels sprouts? I steam or microwave mostly now and am glad to know it’s okay, or even good!

  • The microwave is what surprised me, because so many believe microwaves are bad. I don’t think they have proof just hearsay, so nice to know you can cook in the microwave and retain vitamins.

    Debbie Gore, Recipe for Life

  • I’ve read research before that shows the microwave is often the best cooking method. However, I’m still weary about the heat waves that cook the food in the microwave…not everything is exactly measurable, and I fear that the unnaturalness of microwaves might pose a health risk…but who knows?

  • Eating a selection of raw fruits and vegetables also has the added benefit of being less clarorific.

    Cooking ingredients helps to break down the struture of foods, this in turn helps the digestive systemd subsume more of the ingredients than it could otherwise achieve with raw foods.

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  • Erik Arnesen

    To FoodFitnessFreshair: You have to remember that “natural” is not always the same as “safe” (mercury, earthquakes and ebola virus are natural, too…).

    When you heat food in your microwave, it doesn’t retain the energy waves, and it doesn’t become radioactive – microwaves are electromagnetic waves with a very short wavelength (though much longer than e.g x-rays!). Their energy is converted into heat when they are absorbed by “dipole” molecules (like water)… As long as you don’t stick your head or your hand when it’s on, you shouldn’t be concerned.

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  • Hannah G

    I am curious what affect roasting has on nutrient content as that is my favorite way to eat brussels sprouts.

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