Glycemic Index is Not for Everyone

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.

By Mark Anthony, Ph.D., Contributing Editor

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We’ve gone off the wagon again. Hard as we tried, we just couldn’t stop eating carbohydrates. They taste too good and our beleaguered brains needed the sugar. But just to make sure that we continued to feel guilty about our comfort-food fixation, someone came up with at great idea: Label the carbs “good” and “bad.”

It’s this labeling of carbs as “good” and “bad” that was at the core of the low-carb movement and similar fads preceding it. But as a nation, we didn’t pay attention to the failure of this approach until we sobered up from meat and cheese binge. Sensing the change in consumer awareness, the faddists — lest we abandoned low-carb diets entirely — “gave us permission” to indulge: “OK, you can eat some carbs, but first we’ve got to label them.”

Heaven forbid nutrition should be simple, or (gasp!) we should enjoy our food. The popular nutrition arbiters decided we needed another number to bog us down and that’s what we got. It’s called “Glycemic Index.”

The originators of the Glycemic Index weren’t seeking to spoil our dinner, just to give persons with diabetes and other metabolic disorders some comparative and quantitative data. But something got lost in translation. Suddenly, glycemic index ended up the “be-all and end-all” of carbohydrate nutrition for all people, everywhere, healthy or not.

How Sweet It Is

Glycemic index (GI) is the rate at which the food you eat becomes the sugar in your blood. Developed in the 1970s, its first application was in diabetes — particularly in insulin-dependant diabetes — where it was intended as a guide to closely monitor blood sugar. The theory behind measuring GI seemed sound. As blood sugar rises after eating carbohydrates, insulin, the hormone secreted by the pancreas to help cells take up sugar, rises in response.

A person dependant on an outside source of insulin has a difficult balancing act, matching food with a dose of insulin, keeping blood sugar stable and within normal limits. It’s the sustained elevated blood sugar that leads to the debilitating conditions associated with diabetes.

Thus, the concept is if you know which carbohydrates to avoid, insulin (and thus blood sugar) can be kept under control. Determining GI goes something like this:

First, gather about 10 people and measure their baseline blood sugar. Have each one consume a known quantity of glucose in solution. Measure blood sugar again, then periodically over a couple of hours. Enter this data on a graph and measure the area under the curve. Assign it a value of 100. That’s the measuring stick — supposedly the quickest any food is likely to enter the bloodstream.

Next, feed the volunteers the same measure of different foods, take the same blood sugar data, average it and compare the data with the measuring stick. Run all the foods out on a scale 0 – 100. For example, if the average blood sugar rises 72 percent as fast with one particular food as it does when ingesting pure glucose, the GI is 72 (and so on).

We now have an index of the rate at which food turns into blood sugar, a glycemic index. A score of 70 or above means that the food gets into the blood stream at a rate similar to glucose (a high glycemic index); 55-69 is medium; and 54 and below is considered low.

GI and Obesity

The more recent application of GI has been for weight control where on the surface, it seemed to have relevance. The belief was, if sugar enters the blood stream too quickly, insulin will spike, and your cells will pull up glucose too fast to be used for immediate energy. That will force more glucose to be deposited in cells as fat. Blood sugar will drop dramatically because insulin is still hanging around, leaving you hungry for more carbohydrates. This will make overeating and obesity inevitable.

The theory seemed to make good sense. Many natural carbohydrates like beans and most whole grains have a low GI. Lots of refined carbohydrates like white bread have a high GI. Thus refined foods were blamed for making us fat. It was revolutionary.

So the GI-weight loss connection was embraced by everyone and we all lived happily (and thinly) ever after, right? Not quite. Logical as this idea sounded on the surface, in practice it fails to impress.

Curbed Enthusiasm

The American Diabetes Association concluded in a September, 2004 statement published in Diabetes Care that observing GI along with total carbohydrates can provide additional benefit for blood sugar control. They also concluded the role of low-GI foods in preventing development of type-2 diabetes (non-insulin dependant) was unclear, and that preventing obesity was the most important factor.

So how useful is GI as a tool to combat or prevent obesity? It depends on whose research you read. Proponents point to studies suggesting the benefits of eating certain low-GI foods, such as beans and whole grains. Detractors point to inconsistencies in the research, studies showing no effect and the mixed messages which can be gleaned from reading GI charts.

Yet the GI premise is selling diet books by scores of millions. In books on the South Beach, Zone, Atkins, Glucose Revolution and other diets, GI is treated as the Holy Grail. The only good carb is a low-GI carb, unless of course you’re an athlete.

Studies on athletic performance and carbohydrates show high-intensity workouts deplete glycogen stores, the reserve of carbohydrate that we carry in our muscles and liver for quick energy. We need high-GI foods to replenish this vital reserve. Still, from a dieter’s perspective, a high-GI food translates to “bad carb.” This overpowering guilt by association, with a number on a chart, is what led to the incredibly mixed messages associated with GI.

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
Source: www.nutritiondata.com/glycemic-index.html

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
 
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