Have you ever wondered why you feel terrific after eating some meals—even energetic enough to go out for a brisk walk—while others leave you wanting to curl up on the couch? The culprit could be how fast the foods you eat affect your blood sugar. Typically, the more stable your blood sugar, the more consistently energetic you feel. Foods that send your blood sugar skyrocketing, like candy, can leave you feeling tired and craving more. Foods that take longer for your body to process, such as whole grains and high fiber fruits, release slower into your bloodstream, providing sustained energy without the highs and lows. They’re often a lot lower in calories as well.
By balancing the effects on your blood sugar of the foods you eat, you can sustain energy and reduce calories. This is the notion behind the concept of eating by the glycemic index (GI). Popular low-carb diets such as Atkins and South Beach brought attention to the GI, which rates foods on their ability to raise blood sugar as compared to a standard: one slice of white bread (GI: 70). These diets distinguish between carbs that spike your blood sugar (“bad carbs” with higher glycemic indexes) and those that create a slower release of blood sugar (“good carbs” with lower glycemic indexes). “Atkins tries to get rid of all carbs, which we think is excessive,” says David Ludwig, MD, PhD, director of the Optimal Weight for Life obesity program at Children’s Hospital Boston, who published a study validating the effects of a low-GI diet in
The Lancet. “You don’t have to go to this extreme if you pay attention to glycemic index and choose low-GI carbs.”
Why blood sugar matters
When your blood sugar spikes, your body releases the hormone insulin to move the sugar into your cells to be used for energy. If this happens too often, insulin resistance can develop, which stimulates the release of even more insulin. Persistently high insulin levels can affect your kidneys, blood vessels, and liver, causing abnormal lipid metabolism and high triglycerides (implicated in heart disease). Your ovaries can respond by producing testosterone, leading to polycystic ovarian syndrome, which can cause infertility. These effects are seen in metabolic syndrome, a disorder linked to adult-onset (Type 2) diabetes and heart disease. Metabolic syndrome factors in women include a waist size of 35 inches or more, blood pressure of 130/85 mmHG or higher, a fasting blood sugar of 100 md/dl or higher, triglyceride readings of 150 mg/dl or more, and HDL (“good” cholesterol) of 50 mg/dl or less, say experts at the Cleveland Clinic. You’re at risk if you have three of these five factors.
Two small studies in Boston showed decreased blood pressure and insulin resistance among people who ate a low-GI diet as compared to a low-fat diet, as well as decreased risk factors for heart disease. One of the studies also observed the low-glycemic group felt less hunger and said the GI diet was easier to follow. The Nurses Health Study, an ongoing investigation of nurses’ health habits and outcomes now in its 30th year, showed that women eating the highest GI/load foods had a 50% greater risk of developing Type 2 diabetes and that overweight women eating the highest GI/load foods had twice the risk of developing coronary heart disease as compared to their counterparts eating the lowest GI/load foods.
Eating by the index
A food rated a 70 (remember the slice of white bread?) or higher is a “high” glycemic food; foods rated 56 to 69 “moderately” impact blood sugar, and foods rated 55 or lower are “optimal.” Some investigators also consider glycemic load, which takes into account carbohydrate weights. Raw carrots and a baked potato have similar GIs, but carrots have a lower glycemic load because one serving doesn’t contain as many grams of carbohydrates as does a potato. Processed foods, such as crackers and cookies, have high GIs and loads. Sorry!
Armed with a few simple strategies and a list of low-glycemic foods, you can start right away. Always eat breakfast and at least three meals a day, and include one low-GI food at each meal. Eat at least two servings of fruit and two servings of vegetables every day. Serve beans and other legumes at least three times a week, and combine a higher-GI food with a lower one to lower the overall glycemic effect.
Changing your choices
Instead of this | Choose this |
| Italian bread | Whole grain, sourdough |
| Fruit juice | Whole fruit |
| Popcorn | Peanuts |
| Cheerios | All Bran, slow-cook oatmeal |
| Pretzels | Oatmeal cookies |
| Mashed potatoes | Sweet potatoes |
| Plain bagel | Pumpernickel or rye bagel |
