Why consider a low-glycemic index diet? A high-glycemic meal leads first to a surge, then a crash in blood sugar that makes people get hungrier quicker, which undermines weight-loss efforts.
Define high-glycemic carbs.
Sugar is the granddaddy of all refined carbohydrates. Americans eat close to theft body weight in sugar every year. The second big category is refined-grain products—white bread, white rice, prepared cereals, chips, cookies, crackers, popcorn. They are metabolically similar to sugar. And the third big category is potato products. From a biological perspective, a potato is not a vegetable.
But can't you lose weight with refined carbs if they're part of a low-calorie diet?
You don't get far, because hunger increases and metabolism crashes. So restricting calories while maintaining the same poor diet quality is a recipe for failure.
Does it really make that much difference?
Let me tell you about a study we published June 27, 2012, in the Journal of the American Medical Association. We recruited 21 obese young adults and provided all food to them until they lost 10 to 15 percent of their weight. We knew this would cause their metabolic
rate to fall and hunger to increase.
Then we switched them, for a month at a time in random order, among three types of diets: low-fat, low-glycemic, and a very low-carb Atkins-type diet. Their energy expenditure plummeted more than 400 calories a day after weight loss on the low-fat diet, but hardly at all after the very low-carb diet. In other words, their bodies burned the calorie equivalent of an extra hour of exercise a day just from having been on the very low-carb diet instead of the low-fat diet.
And the low-glycemic diet?
It was in the middle, equivalent to about a half hour of exercise. Based on calories, the very low-carb diet looked the best, but there may be downsides. Many people have a hard time maintaining such a restrictive regimen. Also, the diet increased stress hormone levels, which over the long term could increase the risk of cardiovascular disease. We want to investigate this further.
How can people reduce the glycemic index of their diet?
Say you eat six servings of refined carbs a day. Substitute a serving of non-starchy fruit for one, a serving of beans for another, and a serving of nuts for a third. Each of these is full of fiber and healthy nutrients and supports metabolism. Let's consider breakfast. For years the public was encouraged to eat grain-based, low-fat foods like a bagel with fat-free cream cheese, when in reality, this is just about the worst way to begin the day.
Instead, have half a bagel, make it whole-grain, and top it with peanut butter. Or better yet, eat a vegetable omelet with fruit. Now the carb is balanced with protein, fat, and fiber.