Your Blood Sugar
and Your Weight
Best for Weight Loss
How you can use the concepts of glycemic index and
glycemic load to your health advantage
By Will Block
n the desert Southwest, most hikers and campers are aware of hazards such as scorpions and rattlesnakes. Some, however, forget (or never knew) that one of the greatest dangers they face is water—not the lack of it (we’re assuming they had the foresight to bring some along), but an excess of it, in the form of a flash flood. If you’ve never seen one of these monsters, it’s hard to appreciate how terrifyingly sudden, violent, and destructive they can be.
You’re hiking or, God forbid, camping in an arroyo or a slot canyon. The weather is fine, and you’re unaware that, miles away, there has been a torrential rainstorm that dumped far more water than the parched desert floor could absorb in a short time. The water has to go somewhere, and gravity is the boss. From across a broad expanse of desert, the rushing rivulets converge and are eventually funneled into your arroyo or canyon, where their collective volume and momentum are now enormous. Your first warning that something is amiss is the ominous, rumbling sound of an approaching freight train . . . but there aren’t any tracks out here!
Then it appears, like a nightmare come alive: a chocolate-brown wall of roiling mud roaring down on you, carrying trees, rocks, and anything else that was in its path. It will spare nothing and no one as it smashes through the channel, scouring and reshaping the earth (and exposing new surfaces for geologists and paleontologists to investigate later). Many unwary or unlucky people have met their end this way. The grim reaper comes in many forms, and a desert flash flood is surely one of the most dramatic.
How to Rate a Glucose Storm
Much less dramatic but no less deadly in the long run is a process that occurs in our bodies and that bears intriguing analogies to a flash flood. It’s about glucose (blood sugar), our principal chemical nutrient, and how it gets into our bloodstream following a meal. Just as rain is beneficial in nourishing all the plants and animals on earth, so is glucose beneficial in nourishing all the cells in our bodies.
But, just as too much rain falling too quickly can wind up in the wrong place and do great damage, too much glucose entering our bloodstream too quickly can likewise wind up—indirectly—in the wrong place, doing us harm. What happens is that our excess glucose is rapidly converted to a polymer called glycogen, which is stored primarily in the liver and skeletal muscles. There it serves as a between-meals energy reserve that can be converted back to glucose on demand.
Thus our glycogen levels fluctuate throughout the day. That in itself is normal, but too much stored glycogen results in an unfavorable shift in the balance of fuels that are burned by our cells: we tend to burn more glucose (from the glycogen) and less fat than is desirable, resulting in a gradual accumulation of fat molecules in our fat cells—the “wrong place” mentioned above. This, of course, leads to weight gain, a Pandora’s box that can lead to all kinds of harm down the line. Unlike a flash flood, the damage done by excess glucose takes a long time to accumulate, but it is no less destructive in the end.
Various numerical scales are used to rate the severity of nature’s storms. Similarly, there is a numerical scale to rate the severity of a “glucose storm” from the digestion of carbohydrates. Called the glycemic index (glycemic means “of or pertaining to glucose”), it’s a measure of the rate at which glucose produced by digestion of a carbohydrate-containing food or beverage enters our bloodstream. The more rapidly glucose is absorbed, the higher the glycemic index (GI) of the food. The value for pure glucose itself, taken as a drink (no digestion required) is arbitrarily set at 100, and all other food values are rated relative to this standard. A GI value of 70 or more is considered high; 56 to 69 is medium; and 55 or less is low.
The GI value of some baked white potatoes is a whopping 94, which means that the blood-glucose response, or glycemic response, to the carbohydrates in these potatoes is 94% as great as the glycemic response to the same amount of pure glucose—that’s bad! By contrast, some sweet potatoes have a low GI value of 48—their carbohydrates are digested more slowly compared with glucose (and with the carbs in white potatoes). And some lentils have a very low value of 21—excellent!
Barley, Resistant Starch, and Erythritol—Your Glycemic Friends
Grains are a staple of virtually all diets, and among grains, one stands out dramatically in terms of its potential benefits for glycemic control: barley, especially the type called Prowashonupana. This recently developed cultivar contains about twice the normal amount of a viscous, soluble, indigestible fiber called beta-glucan, which slows down the production of glucose from barley’s digestible carbohydrates.*
With its very low average GI value of 25, barley is an outstanding choice to replace wheat, oats, etc., in a variety of foods. It also has a low average value, 11, of the glycemic load (GL), an important related concept (see the sidebar for an explanation). Incorporating barley in a meal can significantly reduce the average glycemic index, and the overall glycemic load, of the entire meal. For weight control, that’s highly desirable.
Of Chili Peppers and Glycemic Loads
Some chili peppers are hotter—waaay hotter—than others. The heat comes from a compound called capsaicin and is rated numerically on the Scoville scale. The values range from 0 (bell peppers) to about 5000 for Jalapeños to about 250,000 for the fearsome Habaneros to an incredible 1,000,000 for the world champion, the Naga Jolokia from India. Let’s say you decide to live dangerously and go for the Big NJ. First you try a teensy dab of the juice: zzzt. OK—that was doable. Then you screw up your courage and bite into the pepper: A A I I E E E !
Assuming your head wasn’t blown clean off and your tears have subsided, here’s the lesson from that little experiment: the Scoville number was the same in both cases, but the results were wildly different.
See where this is going? Just as with the Scoville number, the glycemic index of a food is a good clue to what could happen, but not an indicator of what will happen. It’s useful to know, but it tells only part of the story. The other part has to do with how much of a given food you consume at one sitting—that makes a big difference, as the chili pepper experiment demonstrated.
To evaluate a carbohydrate-containing food properly, one should combine the glycemic index—which represents, in a sense, the quality of its carbohydrate content—with the quantity of carbohydrate in a typical serving of that food. The result is a very useful figure called the glycemic load. Think of the glycemic load (GL) as the physiological burden imposed on your system by a certain amount of glucose entering your bloodstream at the rate indicated by the food’s GI value. Thus, it’s not the amount alone or the rate alone that matters, but their combined effect.
Calculating a GL value is easy if you know the weight in grams of the food’s carbohydrate content in a typical serving: you just multiply the food’s GI value by that weight, and divide by 100. For example, the GI of some cornflakes is 80, and there are 25 grams of carbohydrate in a typical 1-cup serving. Thus the GL for those cornflakes is (80 x 25)/100 = 20. The vast majority of GL values are in the range from 1 to 40, and most are between 5 and 25. Thus, the GL for cornflakes is fairly high by the standards of most foods—not good.
Some white bread, by contrast, also has a GI value of 80, but the GL for a serving of one slice (containing 12.5 g of carbs) is only 10, which is good. But what if you make a sandwich, which, at last count, requires two slices? Uh-oh—the GI is still 80, but the GL is now 20!
Get the picture? GI is informative, but GL is very informative. Note that the GL values for the various food items in a meal are additive: the sum of the individual loads equals the total load. Adding GI values, however, is meaningless (but one can calculate an average GI for a given meal). Foods such as meat, fish, eggs, alcoholic beverages, and most vegetables have no GI value. No digestible carbs means no GI and, therefore, no GL.
For any given type of food, a low GI and a low GL usually go hand-in-hand, by the way, although not necessarily—there are some dramatic exceptions. Also, GI values for a given food can be highly variable to begin with, depending on many factors, including the variety, the geographic origin, the growing conditions, the producer or manufacturer, the processing or cooking methods, and the consumer’s own digestive system. The GL values will vary accordingly. Don’t sweat the numbers. Just try to minimize those foods that are generally high in GI and maximize those that are generally low.
The best source of information on all this is a book entitled The New Glucose Revolution (available from Life Enhancement Products). The authors are affiliated with the University of Sydney, whose Web site www.glycemicindex.com has the most comprehensive and authoritative tables of GI and GL values for foods and beverages.
- Brand-Miller J, Wolever TMS, Foster-Powell K, Colagiuri S. The New Glucose Revolution, 3rd ed. Marlowe & Co., New York, 2007.
Another aid to slow digestion of carbohydrates is
resistant starch, a relatively indigestible type of starch that also helps to reduce postprandial (after-meal) glucose and insulin levels (we’ll see below why that’s important). And because it’s about 60% indigestible, it reduces caloric intake. Fewer calories is also an attribute of the sugar alcohol erythritol, a natural sweetener that, unlike sugar, does not promote tooth decay. And it’s safe for diabetics because it does not increase glucose or insulin levels.
Glucose and Insulin Spikes Are Harmful
By definition, consuming a high-GI food means that your blood glucose will rise to higher levels, more quickly, than it would if you consumed an equivalent amount (in terms of carbohydrate content) of a low-GI food. And what’s so bad about that? Plenty!
The glucose spike triggers an insulin spike, which drives
glucose levels down sharply. More slowly digested foods keep glucose and insulin levels fairly even throughout the day.
When a large amount of glucose enters your bloodstream rapidly, as occurs when you consume a significant amount of a high-GI food, such as white bread or potatoes, you get a glucose “spike.” Your body quickly responds with an insulin spike in order to bring the glucose levels down as quickly as possible (but it’s not instantaneous—it does take time, and time is the enemy in this case). Although occasional spikes are nothing to worry about, we do need to worry if our habitual consumption of high-GI foods makes these spikes a daily occurrence over long periods of time—years or decades.
The reason for this is that both glucose spikes and insulin spikes promote weight gain and are harmful to our tissues and organs in the long run, producing incremental damage that keeps on accumulating. (Excessive insulin levels are responsible for the unfavorable shift in fuel consumption, which favors fat accumulation, mentioned earlier.) The most insidious effect of these spikes, besides promoting weight gain, is a closely related one: the promotion of insulin resistance, which makes the body’s vital task of maintaining glucose control, or glycemic control, that much more difficult. Insulin resistance is a major component of the metabolic syndrome, and it’s the principal precursor to type 2 diabetes, which is characterized by excessive levels of glucose (hyperglycemia) and, often, excessive levels of insulin (hyperinsulinemia).
Confirmed: Glycemic Control Is Effective for Weight Loss
And what is the principal precursor to insulin resistance? Obesity, which is also associated with increased risks for hypertension and high cholesterol. And the cure (or, better yet, prevention) for obesity? Diet and exercise. Exercise is easy—just do it. But what diet? They’re too numerous to contemplate, and the vast majority of them don’t work in the long run. Many of them, recognizing the potential dangers of “glucose abuse” from too many carbohydrates in our foods, focus on reducing the carbs, period. But that’s a brute-force approach that is not only very hard to adhere to (we love our carbs!) but that also carries potential risks of its own, by shifting our dietary intake too much toward protein and fat.
A subtler and wiser approach to carbs is to select them more judiciously, based on their GI values. Various studies have suggested that this approach to glycemic control can be effective for weight loss—and now a meta-analysis of the literature has confirmed that.*
Examining Low-GI Diets vs. High-GI Diets . . .
A group of Australian researchers examined 68 clinical weight-loss trials and narrowed them down to six that met all of their inclusion criteria for the meta-analysis. These six randomized, controlled trials compared the effects of low-GI or low-GL diets (the test diets) with those of high-GI or high-GL diets or any conventional weight-loss diets (the control diets).* The difference in overall GI value between the test and control diets in these studies was typically about 25–30 points.
© iStockphoto.com/Liza McCorkle/christopher o driscoll
The trials, which were conducted in Australia, Denmark, France, South Africa, and the United States, involved a total of 202 overweight or obese participants, none of whom had diabetes. Their average ages ranged from 16 (in the one study that included children) to 46. The dietary interventions ranged from 5 weeks to 6 months in duration, and the maximum length of follow-up was 6 months.
The primary outcomes of interest in these studies were body mass and fat mass. Of secondary interest in some of the studies were insulin action (i.e., the degree of insulin sensitivity or its converse, insulin resistance), glycemic control, and cardiovascular risk factors (mainly lipid levels and blood pressure).
. . . Reveals Greater Weight Loss with Low-GI Diets
The primary finding of the meta-analysis was that a low-GI or low-GL diet induced greater weight loss—by 1.1 kg (2.4 lb), all of it fat—than the control diets. There was also a small but significant decrease in body mass index.
Compared with the control diets, the test diets brought about increased insulin sensitivity (i.e., reduced insulin resistance), but with no evidence of glycemic control. That sounds surprising, doesn’t it? But because diabetics were excluded from all the studies, glycemic control was not expected to be a significant factor in the outcomes; only one of the six studies measured it, and there was no significant change. The test diets also reduced total cholesterol and LDL-cholesterol (the “bad cholesterol”) but did not affect blood pressure.
The authors concluded,
Overweight or obese people on low-glycaemic-index diets lost more weight than those on high-glycaemic-index diets or conventional energy-restricted weight-loss diets, with the change in body mass, total fat mass, and body mass index all significantly decreasing after the low-glycaemic-index diet compared to the comparison diet. It may be easier to adhere to a low-glycaemic-index diet than a conventional weight-loss diet, since there is less need to restrict the intake of food as long as low-glycaemic-index carbohydrates are predominantly consumed. . . . Hence, lowering the glycaemic index of foods in the diet appears to be an effective method of losing weight, particularly for the obese.
And it’s easy to do! So don’t get caught in a flash flood—start your glycemic control program today.
- Thomas DE, Elliott EJ, Baur L. Low glycaemic index or low glycaemic load diets for overweight and obesity. Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No. CD005105.
Will Block is the publisher and editorial director of Life Enhancement magazine.