Understanding glycemic load

Unfortunately, because of the low-carb craze, carbs have gotten a bad name. Very-low-carb diets (those that restrict you to 30 grams or fewer total carbs per day) require you to eliminate fruit and starchy carbs (legumes, grains and starchy vegetables) from your diet altogether, but by doing so, you miss out on the essential vitamins, minerals and phytonutrients that these foods supply. These diets can also cause constipation and digestive problems because of their low fiber content and fiber is another beneficial product of carbs. Fiber helps you feel fuller longer, which can help you eat less. Carbs are also important sources of energy for your body, supplying glucose, which provides energy for the brain and central nervous system.

On the other hand, some diets and eating plans, including the United States Department of Agriculture's (USDA) Food Guide Pyramid and the Canada Food Guide, promote a high-carb diet, one in which approximately 60 percent of your daily caloric intake comes from carbs. However, a meal that's too high in carbs can cause a rapid rise in blood sugar (glucose) levels. In response to this, the pancreas secretes excessive amounts of insulin, a hormone that helps regulate blood sugar levels.

Insulin lowers blood sugar levels by promoting the uptake of glucose into most of your body's cells, especially the muscles, liver and fat cells. Excess insulin causes rapid absorption of glucose. As a result, blood sugar quickly falls below a critical level, and your body calls out for more glucose, which the brain requires in order to function. Thus, you experience carbohydrate cravings and blood sugar swings. Insulin also stimulates your liver to convert and store excess sugars as fat.

So it makes sense not to go overboard on the amount of carbs you consume. For many people, a more reasonable approach is to try to consume a moderate amount of healthful carb-containing foods along with an adequate amount of lean proteins and healthful fats.

Glycemic Index and Glycemic Load

Some people use the glycemic index (GI) rating of a given food to determine whether or not to include it in their diet. The GI is a measure of the rate at which a carb breaks down and releases glucose into the bloodstream; the higher the GI, the greater the effect on insulin secretion. Generally speaking, the more processed a food is, the higher its GI.

For example, fruit juices have higher GIs than their whole fruit counterparts, and flours (and foods made from them) generally have higher GIs than the whole grains from which they're ground. Eating protein and fats with carbs tends to slow down the carbs' rate of entry into the bloodstream, thus lowering their glycemic effect.

One of the drawbacks of using only the GI is that it can be misleading. GI tests aren't based on typical portion sizes of foods. Instead, researchers use a standard measure of 50 grams of carbohydrates of the foods that they are testing; therefore, portion sizes vary depending on the amount of available carbohydrates in the particular food. For example, a carrot contains only 4-6 grams of available carbs, so you'd need to eat about 10 carrots to consume 50 grams of carbohydrates--and nobody eats that many carrots at one meal! Many people avoid carrots and other nutritious high-GI foods such as beets and squash because of their higher GI values. This is where the glycemic load (GL) proves more useful.

GL is a relatively new tool that takes into account the GI as well as the amount of carbohydrates in a typical portion size of a given food. As an example, in some studies, carrots have a high GI rating of 92, but one medium carrot has a low GL rating of approximately 5. In contrast, white rice has a low GI of 51, but because it has a high amount of available carbohydrates, a l-cup serving has a high GL rating of approximately 21.

Highly processed foods, starchy high-GI foods such as white bread and white rice, and foods and beverages that contain a lot of sugar such as cakes, cookies, candy and soft drinks generally have high GL values and are lacking in nutrients that are crucial to your body's handling of carbs.

Many of the low-carb eating plans supply lists that contain the carb content of individual foods. The problem with this approach is that it requires you to count the number of carb grams that you consume, and for some people, this is more trouble than it's worth. After all, eating is one of the great pleasures in life. If you're one of the people who doesn't want to count every carb gram or calculate your protein requirement or Weigh and measure every bit of food you plan to put into your mouth, then you might want to try the following suggestions instead.

Simpler Method

A simpler method is to choose the majority of your carbs from those that have low or no GL ratings (see chart, p. 28). These foods help keep blood sugar levels stable and provide vitamins, minerals, phytonutrients and fiber.

Non-starchy vegetables have no glycemic values because they don't contain enough carbs for glycemic testing to be feasible, so feel free to load up on these foods. As a general guideline, fill half of your plate with cruciferous vegetables--such as broccoli, kale, cauliflower and cabbage--and/or other non-starchy vegetables, particularly leafy greens.