Thursday, October 14, 2010

Thoughts about nutrition

The next time you're in the grocery store walking down the cereal aisle, check out the different kinds of oatmeals. For those of you who are not oat enthusiasts like me, you may be surprised to discover how many different kinds of oatmeals there are: instant oat, quick oats, old-fashioned rolled oats, and steel-cut oats. Many people haven't heard of steel-cut oats. Rather than being rolled flat into a soft, fluffy morsel, a steel-cut oat—sometimes called a groat—has a hard nutty texture that more resembles a Grape Nut than a traditional oat. But chemically it's the same oat as any other.

While you're checking out the different oatmeals, note their nutritional profiles. What you'll see is that each oat is nutritionally identical to the others according to the standard nutrition label. Given an equal serving size by weight, each has the same amount of fat; carbohydrates, including sugar and fiber; and protein. The only thing that differs is the volume of a serving; steel-cut oats are denser than the rolled oats and thus have a smaller serving size by volume, typically a ¼ cup instead of rolled oats' ½ cup.

This similarity is probably what you'd expect. Since the difference in oatmeals has to do with how the oat has been milled—what we called in elementary school science a physical change rather than a chemical change—their densities are different owing to each individual oat's different shape, but their nutritional profiles should be the same.

Only, there's one problem here. Try eating instant oats each morning for a week or two, and try eating steel-cut oats each morning for a different week or two. The sameness of their nutritional profiles suggests that there should be no difference in the effect of your body's digestion of the different oatmeals, but what you'll probably find is that steel-cut oats keep you feeling fuller longer. Not a lot longer, but longer nonetheless. How can this be?

The explanation has to do with the glycemic index, which is to say that steel-cut oats take longer for your body to digest. That they take longer to cook than instant oats is not coincidental; the physical shape of the individual oat itself determines its break-down period, whether it's cooking in a pot on your stove or breaking down into simple sugars in your gut. The standard nutrition label is helpless to explain this difference because it seeks to describe nutrition molecularly by classifying nutrients chemically. Some molecules are lipids; others are sugars and so on. But the macro-scale physical shape of a food particle can have a profound effect on its digestion.

Nutrition is more complicated than the standard nutrition label suggests. This complexity becomes evident when you begin mixing foods as we do in the real world for real meals. For example, fruit juice digests faster than actual fruit. Thus, you can opt for steel-cut oats for a longer, steadier source of energy through the morning hours but kill the result by drinking your breakfast orange rather than eating it. Or you could opt for the convenience of whole wheat toast, which, despite being a whole grain and supposedly healthful, is made from flour and is absorbed quickly by the body, but additionally eat two apples so as to slow down the body's digestion of the toast because apples are terribly fibrous and require lots of time for absorption even though they are chock full of sugar. Smother almond butter on the toast or better still, eat a few whole almonds. A pantry of just a few foods can lend itself to a combinatorial explosion of possibilities.

I think it's fair to generalize a broader point from this example, and that is this: a useful, practical understanding of nutrition does not follow from simple, linear cause-and-effect relationships. The healthfulness of a meal is not the simple sum of each food's constituent parts. Instead, the effect of any food you eat is dependent upon the context of the other foods that are eaten as well. As mentioned above, eating an apple or two will add a lot of sugar to a meal, but the end result is likely to be slower absorption of the rest of the meal than if one eats whole wheat bread instead of the apples, though the bread will have less sugar. Sometimes the differences are purely physical and not chemical, such as with different types of oats.

This is not a bad sort of complication. This doesn't mean that we're hopelessly ignorant of knowing what we should be eating. Rather, it means that often we can ignore the countless minute details of our foods' compositions and focus on the bigger picture. One of the more profound points I've discovered through years of trying to eat healthily is that in many ways the minutiae of calories, protein, fat, sugar, vitamins RDAs, and so on can and should be chucked to avoid drawing one's attention away from what really constitutes a healthful meal. And what makes such a meal? That is something each of us must learn on our own, first by learning some of the science but ultimately by listening to our bodies.

2 comments:

Diamond Girl said...

Listening to our bodies? Hmmm....my body seems to always be asking for tootsie rolls. And I say yes!

cmbrandenburg said...

Diamond Girl—whatever works for you!