Q: I’ve heard that to lose weight I should eat according to the “glycemic index.” What is it and will it really help me lose weight? —Linda Martin, Florida

A: Although a stream of diet books has recently touted the glycemic index (GI) as the latest and greatest way to lose weight, the GI is actually not new. It was developed more than two decades ago by researchers who wanted to measure the effect of carbohydrate-containing foods on blood sugar levels. It was created for research purposes—not as a consumer weight loss tool. But because it occasionally rises in popularity, let’s take a look at what it is and what it really means for your waistline.


During digestion, the carbohydrates you eat are broken down into glucose, which enters your bloodstream to be transported to the places where it’s needed for energy, such as your muscles and brain.

So when we talk about blood sugar levels, we’re talking about the amount of glucose circulating in your blood. You obviously need some glucose in your bloodstream to supply your body with energy. But consistently having blood sugar levels that are too high can be a problem, as in diabetes.

The GI rates certain foods (on a scale of one to 100) in terms of how much they’ll raise blood sugar levels when compared with an equal amount of pure glucose (which has a reference score of 100). For example, a serving of boiled white potato has a GI of 54, meaning that it raises blood sugar levels by a little more than half (54%) of what an equal amount of glucose does.

Diets structured around the GI emphasize eating low-GI foods, or foods with a GI of 55 or less. Medium GI foods are those with an index of 56 to 69, and high-GI foods are those that are indexed at 70 or more. You’ve probably heard that if you’re going to eat a high-GI food, then you should pair it with a low or medium-indexed food to slow its effects on your blood sugar levels.

The amount of glucose that ends up in your blood after you eat depends on lots of factors, including how much food you ate, the amount and type of carbohydrates in the food and how the food was processed or prepared—for example, pasta cooked al dente could have a lower GI than pasta that’s boiled until it’s really soft.


So, the question remains: Is the GI useful to the average person trying to lose weight? The answer: probably not as much as other tried-and-true weight loss methods—namely, counting calories and controlling portion sizes.

It’s true that keeping blood sugar levels in balance and preventing them from spiking and dipping may help control hunger and curb overeating. So if you think the GI will help you in that regard, then go for it. There’s even a database in a university-based web site, www.glycemicindex.com, that can help you find the GI levels of foods.

But here’s the rub: In your everyday life, do you eat only single foods, or do you eat mixed meals? I’m betting you mostly eat mixed meals, in which case the glycemic effect of high-GI foods is likely to be stunted if they’re eaten at the same time as low-GI foods. For example, if you eat a high-GI baked potato at the same time as low-GI broiled chicken and steamed broccoli, then the effect of that baked potato on your blood sugar level is likely to be inhibited by the low glycemic effect of the other foods. You may already be eating this way and didn’t even know it!

My advice for losing weight is this: Make vegetables, whole grains, legumes and lean sources of protein the basis of your diet, cut down on the amount of high-calorie treats (like french fries, cookies and pastries), watch your portion sizes, and make sure you burn more calories than you consume.

Don’t get too hung up on the GI—that time might be better spent taking a walk and burning some calories!