Nutrition Beyond the Trends: G.I. Blues
This month, Dr. Mark Anthony warns us of a new twist on the old low-carb nutrition fad. Handy as it is for diabetics, the Glycemic Index isn’t the “be-all and end-all” of carbohydrate nutrition for everyone.
Ironically, the “good carbs” and “bad carbs” labeling runs contrary to the most important revelation that came from GI research. “Complex carbohydrates” (starches) did not all have a low GI as predicted. We had previously assumed that since starches were aggregate chains of glucose molecules, they would have the lowest GI, but this was only partially true. For example, white bread had a GI nearly equal to that of pure glucose, while some sugars had a GI much lower than predicted.
As it turns out, a number of different factors affect how fast sugar enters the blood. The absurdity is that the GI of some foods has nothing whatever to do with the health benefits of that food. For example, fat slows the rate at which the stomach empties into the small intestines. That means if a food is rich in fat, it will have a low GI. Makes sense for a food such as walnuts, which are a healthy source of monounsaturated fat and low in carbs.
But now let’s look at potato chips. They’re high in carbs, yet have a low-medium glycemic index of 55. Mashed potatoes — an outstanding source of complex carbohydrates and other nutrients — weigh in at a whopping 98.So What’s the (GI) Message?
Apparently, if you want to lose weight, potato chips are the way to go. In fact, if you go by the GI weight-control plan you encounter a number of such incongruities: Carrots are a high-GI food, jelly beans are “better” than potatoes and crispy rice cereals are superior to cooked whole-grain brown rice.
These “messages” we take from the GI charts are muddled because the list of things that alter GI is so large: fat, protein, fiber, food particle size, cooking method, moisture content, type of starch (amylose or amylopectin), type of sugar (glucose or fructose — even how well you chew your food. It all varies from person to person, and even in the same person at different times or under different circumstances.
During the anti-carb frenzy, GI was applied almost arbitrarily in assigning “good/bad” labels to foods. Beans were good, but potatoes, carrots and most fruits became bad guys. Eventually, it dawned on enough consumers that this didn’t make sense. From the point of view of those who pushed the anti-carb movement, something had to be done.
A correction factor was needed to calculate ourselves out of this mess. So, we multiplied the GI times the grams of carbs in a food, and — voila! — “glycemic load” was born. Glycemic load would now act as a sort of qualifier for the glycemic index.
Glycemic load had to be created to field questions from consumers catching on to the low-carb conundrum. Again, the answer was oversimplified, leading to the following muddle: If a food is not high in carbohydrates, it has a low glycemic load, regardless of how quickly the sugar is metabolized into the blood. If a food is high in carbohydrates, it may or may not have a high glycemic load, depending on all the other factors that affect the rate of absorption of carbohydrates.
One of the weaknesses of high-GI foods is that they spike insulin levels and leave us hungry too soon after we eat. This is called the satiety index. It works like this: Feed a bunch of volunteers a measured amount of single foods and see how satisfied they feel three hours after they eat. Give white bread, supposedly the least satisfying carb because of its high GI, the standard score of 100 — the same as glucose. A score of 150 means the food is 1.5 times as satisfying as white bread.
By these standards, the highest ranking food is boiled potatoes, spiking nearly off the charts for satiety and more than three times higher the satiety factor of white bread, yet it has a similarly high GI and a high glycemic load.Much Ado About the Wrong Thing
In the end, GI is a just one more characteristic of a food — a “result,” not a cause. It tells something interesting, namely that many things affect how fast the food we eat becomes the sugar in our blood. But, just as calories don’t give a complete picture of food value, GI misses the mark as the measure of carbohydrate value.
If, in reading a GI chart, one concludes it is a good idea to eat more beans and whole grains, great. But if this numbers game frightens people away from eating healthy, population-sustaining foods such as carrots, potatoes, bananas and dates, then the glycemic index/glycemic load approach to diet is as useless as any of the other misguided, or even blatantly deceptive, nutrition fads that came before.
|Glycemic Indexes and Glycemic Loads for Common Foods|
The table below shows values of the Glycemic Index (GI) and Glycemic Load (GL) for a few common foods. GI's of 55 or below are considered low, and 70 or above are considered high. GL's of 10 or below are considered low, and 20 or above are considered high.
|GI and GL for Common Foods|
|Food ||GI ||Serving Size ||Net Carbs ||GL|
|Peanuts ||14 || 4 oz (113g) ||15 ||2|
|Bean sprouts ||25 || 1 cup (104g) ||4 ||1|
|Grapefruit ||25 || 1/2 large (166g) ||11 ||3|
|Pizza ||30 || 2 slices (260g) ||42 ||13|
|Lowfat yogurt ||33 || 1 cup (245g) ||47 ||16|
|Apples ||38 || 1 medium (138g) ||16 ||6|
|Spaghetti ||42 || 1 cup (140g) ||38 ||16|
|Carrots ||47 || 1 large (72g) ||5 ||2|
|Oranges ||48 || 1 medium (131g) ||12 ||6|
|Bananas ||52 || 1 large (136g) ||27 ||14|
|Potato chips ||54 || 4 oz (114g) ||55 ||30|
|Snickers Bar ||55 || 1 bar (113g) ||64 ||35|
|Brown rice ||55 || 1 cup (195g) ||42 ||23|
|Honey ||55 || 1 tbsp (21g) ||17 ||9|
|Oatmeal ||58 || 1 cup (234g) ||21 ||12|
|Ice cream ||61 || 1 cup (72g) ||16 ||10|
|Macaroni and cheese ||64 || 1 serving (166g) ||47 ||30|
|Raisins ||64 || 1 small box (43g) ||32 ||20|
|White rice ||64 || 1 cup (186g) ||52 ||33|
|Sugar (sucrose) ||68 || 1 tbsp (12g) ||12 ||8|
|White bread ||70 || 1 slice (30g) ||14 ||10|
|Watermelon ||72 || 1 cup (154g) ||11 ||8|
|Popcorn ||72 || 2 cups (16g) ||10 ||7|
|Baked potato ||85 || 1 medium (173g) ||33 ||28|
|Glucose ||100 || (50g) ||50 ||50|