I wrote an earlier post on the whole idea that sugar is sugar is sugar, dealing with maple syrup, honey, and molasses. At some point I want to write about more of these sweeteners, including agave nectar and brown rice syrup, so stay tuned for that. I also want to deal with what I call “sugaroids,” substances that contain sugar plus something else (alcohol! chlorine!) but since they are not “real” sugar, and since they contain fewer calories than sugar, items made with them can be labeled “sugar free.” This is the type of thing that, like so many other weird dietary ideas, makes me want to tear my hair out. But for now I want to talk about another hair-tearer: the infamous glycemic index. As you might guess (to quote my son when he was a toddler), “I don’t wike dat.” The whole idea is so misguided, and has led to so many people refusing to eat perfectly healthy food, that I think it’s worth a post. (And yes, it should be “healthful” food, but cut me some slack.)
On first blush, the GI seems sensible. It’s a measurement of how high your blood sugar rises in response to eating various foods, with the lower numbers being better. We all want to avoid the dreaded “blood sugar spike,” don’t we? If you confine yourself just to eating low-GI foods then you should be healthier. But there are big problems with how these numbers are determined. “And how are they determined?” you may ask. Here’s the rundown:
- People with normal blood sugar are used as test subjects and fast for 12 hours before testing various foods.
- They ingest measured amounts of the foods being tested in isolation.
- Because the measurement of the food is often unrelated to a normal serving, the GI numbers for some perfectly healthy foods come out as very high.
Let’s take a food that’s always used as a good example of the bad science behind this index: watermelon. This fruit, like most, is almost totally water. The standard intake of carbs from a portion of food being tested is 50; in order to take in that many from watermelon you’d have to eat, like, a ton. Or a bunch. To put it another way, 50 grams of watermelon has a GI of 80, but that’s only if you eat enough of the fruit to give you that many carb grams minus the water and fiber. A normal serving of a cup or so of diced watermelon has a GI of 5-7. It’s a perfectly acceptable thing to eat and won’t raise your blood sugar appreciably unless you eat the aforementioned ton. And who would want to do that? I’ve always thought watermelon is pretty boring. (Although Greek watermelon is pretty good; you have to go to Greece to get it, though.)
Notice that the GI standard has been set using people with normal sugar metabolism. We have no idea how someone with diabetes, for instance, would actually process these foods because they weren’t involved in the original study. Notice also that these foods are eaten in isolation. When is the last time you ate plain mashed potatoes at 7:00 in the morning? I’m going to guess never. And the high GI of those mashed potatoes (plain, remember) is just for the flesh. If you include the skin, which of course introduces a bunch of fiber (as well as many vitamins and minerals that are found right under the skin), you’re going to lower the GI significantly. (But since every potato variety is different there’s no standard measure possible.) I myself pretty much always leave the skin on potatoes, even for potato salad. (More on that item in a minute.) Which leads to another question: Do you ever eat the skin on sweet potatoes? You can, apparently, although I’ve never tried it. So now think this through with me here: although the plain flesh of a white potato has a higher GI than the plain flesh of a sweet potato, a white potato with the skin would almost certainly have a lower GI than a peeled sweet potato. You could put the same amount of butter on each potato (and adding fat lowers the GI number because carbs + fat are absorbed more slowly than carbs alone) and come out with the buttered skin-on white potato having a less-drastic effect on your blood sugar than the buttered and peeled sweet potato. I say this as someone who really likes sweet potatoes, so there’s no malice here against them. (A sweet potato isn’t a potato, or a yam, but I think we’ll just pass softly by that whole quagmire.)
And then, just to add yet another layer to the puzzle, if you cook white potatoes and then cool them, as you do for potato salad, the starch gelatinizes and is made less immediately available, thus lowering the GI even more. (I make potato salad with red or Yukon Gold potatoes which have thin skin, and, as always, I leave the skin on.) Since potato salad usually has some kind of high-fat dressing such as mayonnaise, the GI is lower still. (But the calories are high. And calories do count, sorry to say, regardless of what you may have heard.)
So you say, “But I thought there was another measure called the ‘glycemic load’ that’s a better measurement of blood-sugar impact than the glycemic index. How about that?”
Glad you asked! Let m go back to the watermelon:
Here are two examples: Watermelon has a high GI of 72, yet a low GL of 7.21. The high GI is based on 5 cups of watermelon, not an actual serving size of 1 cup. The low GL means one serving of watermelon doesn’t contain much carbohydrate, because it is actually mostly water. The low GL indicates that a serving of watermelon won’t have much impact on your blood sugar.
Carrots are another example of a low GL food that many people think will raise their blood sugar a lot — but it’s not true. That’s because carrots have a high GI of 71. However, what most people don’t know, is that the GL for carrots is only 6. Therefore, unless you’re going to eat a pound and a half of carrots in one sitting, an average serving of carrots will have very little impact on blood glucose levels. That said, juicing carrots — which means consuming more carrots at once — will have a greater impact on blood glucose. (from “Glycemic Load and Glycemic Index: What’s the Difference and Why Does It Matter?” by Riva Greenberg in The Huffington Post, quoting a registered dietician and certified diabetes instructor Susan Weiner—please note Weiner’s credentials!)
Let me point out a couple of things just from this brief quotation: 1) Can you believe that anyone would actually tell people not to eat carrots because they have too much sugar? But I actually know someone who was told by “nutritionist” (a term that has no legal meaning in the state of Colorado) not to eat carrots for that very reason, and 2) Juicing is for the birds! Why on earth would you want to drink your food? Don’t juice your vegetables, and don’t drink fruit juice. (I can speak with some authority on the juicing topic, as my dear mother was a very early proponent of juicing back in the 1960’s. I can still remember how noisy the machine was, and the piles of bright orange carrot pulp that were left behind. In other words, just as the above quotation says, she was producing carrot sugar water–with some vitamins, of course, including beta carotene. And what did she do with the carrot leavings? She put them in her compost bin.)
Well, as I so often say, I’ve gone on long enough. Could we all just be, like, sensible? Or is that too much to ask?