Vegetable Cooking Methods

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Anybody who has read our What Makes Us Different section knows that I am not crazy about oversimplifications.  Yet, I can understand why they happen.  Some topics are just too complex to be explained in a factoid, meme, or sound bite, so information is rounded off and oversimplified in order to shove it into said formats.  This is most certainly the case when it comes to answering the question, “Which cooking method is best for retaining nutrients in vegetables?”

For example, I look on one site and see an illustration endorsing steaming while vilifying microwaving, while another suggests microwaving.  Who is right?  They are both oversimplifying, which is what leads to the apparent contradiction and confusion.  The true answer depends on the exact question being asked, including such factors as the particular vegetable, cooking conditions, and specific nutrient(s) of interest.

To give yourself a sense of the complexity, take a look at this 2009 article in the Journal of Food ScienceScroll down to pages four and five where you see the tables showing the changes in antioxidant activity in the various vegetables after being cooked in different ways.  Don’t worry about the numbers or what the acronyms and terminologies mean.  Let me just call your attention to a few themes.

  1. Cooking a given vegetable in a particular fashion can help in one way and hurt in another.  Multiple tables, not just one, show antioxidant activity because individual nutrients react differently as they are cooked.  For example, according to the tables, microwaving celery reduces its LOO radical scavenging capacity (again, don’t worry about the acronyms and terminology – that’s not the point) while the same exact cooking method actually boosts its OH radical scavenging capacity.
  2. Anybody who preaches the virtues of always eating raw is overgeneralizing; in some cases, cooking can help you get more nutrition out of your foods.  Look at Table 4 and notice all the dashes and negative numbers.  Those dashes indicate no losses after cooking compared to when the vegetable was raw, and negative numbers indicate that the antioxidant activity was increased, not reduced, by cooking.
  3. No single cooking method is going to be best for all vegetables.  Pick almost any column in Table 2, 3, or 4, and you will see it is comprised of positive numbers, negative numbers, and dashes.  Check out the griddling column in Table 2, for example, and you will see eight positive numbers, six negative numbers, and six dashes.  This indicates that griddling reduced LOO radical scavenging capacity in eight of the vegetables, boosted it in six other vegetables, and left it unchanged in the remaining six.
  4. No single study is going to tell us everything we want to know.  Science is much more complex than that.  Consider that this is just one of many studies that investigated the effects of cooking methods on vegetable nutrients.  It examined this particular group of vegetables for changes in three nutrients according to the specific cooking conditions explained in Table 1.  Do you think it might make a difference if they baked the vegetables at 150oC or 250oC rather than 200oC?  What if they cooked the vegetables for half the time, or twice the time?  What if they fried them with sunflower oil instead of olive oil?  What if they used a different variety of onion?  What if they had chosen to examine other nutrients, such as vitamin C or calcium?

Wow, this is getting confusing, isn’t it?  If you are even still reading this, you are probably one of the few (Hi, Mom!) who kept going after the first paragraph or two.  You can see then how tempting it is to oversimplify.  I almost want to do it myself right now, but instead I will leave you with a question.

How do you like your vegetables?

I am reminded of a conversation I had with a patient a few months ago after he switched to me from another dietitian.  His previous dietitian told him which vegetables he should eat raw, which ones he should cook, how he should cook them, etc.  I know she meant well, and I am sure some patients are looking for those kinds of orders.  As this man said to me though, “She should just be happy I am eating any vegetables at all!”  We need to remember that you are neither a lab animal nor a case study in some nutrition school homework assignment.  You are a free-living person with feelings and other factors that influence your decisions.  It isn’t all about numbers.  We need to remember the context.

Personally, I don’t care that microwaving my celery would boost its OH radical scavenging capacity by approximately 39.3%; the idea of softening a vegetable that I enjoy for its crunch sounds pretty unappealing to me.  Just let me have my ants on a log and I’ll go on my merry way.

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