Friday, November 18, 2011

What is a vegetable?

The morning headlines are telling us that Congress has declared pizza to be a vegetable.  Pundits around the world are reacting to this news from every conceivable point of view.  I will leave the nutritional arguments to nutritionists, the political arguments to the Occupy Wall Street movement, and making fun of congress to Jon Stewart.  So what is the botanical perspective?

First, one must note that congress did not actually declare pizza to be a vegetable. That was a revision made by the “media,” to make the story more sensational.  Congress was simply legislating that tomato sauce is a vegetable, and that the amount found in a pizza qualifies the latter as a balanced meal (something college students have always known).  Again it is basically a nutritional/political issue, but perhaps I can address the point of whether or not tomato sauce is a vegetable.

Botanically, there are widely varied definitions of the word “vegetable.” It is not an officially defined technical term.   The plant kingdom has at times been referred to as the “Vegetable Kingdom,” and if you’ve ever started out a round of 20 Questions by asking “animal, vegetable, or mineral,” you’ve employing that definition.  So by that definition, anything that comes from a plant is a vegetable, including wheat flour.  A pizza, if totally vegan, could therefore could be classified as a vegetable, along with donuts, chocolate chip cookies, and fruit loops.  Now if the members of congress had boned up on their botanical history, they could have used that definition and made this whole debate a lot simpler.

It is more useful to break down the different categories of plant parts, and consider their role in nutrition.  In terms of the parts we eat, we can consider the following classification:

1.       Leaves and stems – these are your hard-core vegetables, low in carbs, high in vitamins, minerals, and fiber.  This is what nutritionists are talking about with respect to improving the quality of school lunches.
2.       Seeds – these are the structures containing embryos and stored food for the next generation of plants.  They include peas and corn, which are considered “starchy vegetables,” along with various kinds of beans, which are sometimes considered vegetables, sometimes not.  Actually a kernel of corn (maize to the rest of the world) is botanically identical to wheat, oats, barley, etc., and we don’t consider popcorn, corn muffins, or fritos to be vegetables, so corn is marginally a vegetable at best.  The “baby corn” popular in oriental cooking works better, because it hasn’t stored up the starchy reserves yet. (technically, corn, wheat and other cereal grains are single-seeded fruits with a very thin, hard fruit wall – but that’s getting into botany geek territory and we don’t have to go there).
3.       Starchy roots and other underground structures.  Many plants store food underground for use in the next growing season.  They are loaded with starch, and so can contribute a lot of calories.  Carrots, beets, and radishes are true roots, as are sweet potatoes, but white potatoes are specialized underground stems called tubers.  Onions might have the best claim to be true vegetables, since they consist of compact cluster of specialized leaves, but they also store carbs and are calorie-rich. 
4.       Fruits – technically a fruit is a structure that encloses seeds in plants, but many fruits that are not sweet are used as vegetables: peppers, eggplant, okra, cucumbers, squash, green beans, and … tomatoes! So botanically speaking tomato sauce is a fruit product, but we yield to common usage on this point, because tomatoes are low in sugar, high in vitamins, lycopene, etc.  Tomato sauce can therefore be considered at least a vegetable product, along with ketchup. The problem with these is what else is in them – like up to 60% of your daily allowance of sodium in a cup of tomato sauce.

So, from a botanical perspective, you can use the word vegetable in almost any way you want in reference to the parts of a plant, and so it becomes irrelevant nutritionally unless carefully qualified.   Nutritionists should have the final say, because it’s what’s in those vegetables and vegetable products, and the overall balance between the different food groups that is the issue.