Lately, many nutrition gurus have been trying to tell me that eating a diet with a low glycemic index is the secret to losing weight. But if that were true, then carrots would be more fattening than fudge is.
Unfortunately, the glycemic index is being used to steer people away from the sort of food that can really help them lose weight and control their blood sugar: unrefined starches and vegetables. If you survey the world’s populations, you’ll find that the people who are eating diets based on unrefined starches and vegetables have low risks of obesity, heart disease, diabetes, and breast cancer—even though the glycemic index of their diet is high. In contrast, the people who are eating the most fat and protein—both of which tend to decrease the glycemic index of a meal—are the ones who are getting fat and sick.
The glycemic index was originally developed to fine-tune the system of carbohydrate exchanges that people with type 1 diabetes use to calculate how much insulin they will need to inject after a meal . The glycemic index measures the effect that 50 grams of carbs from any given food has on your blood sugar. For example, if you ate 50 grams of carbohydrate from beans, your blood sugar wouldn’t go as high as if you ate 50 grams of carbohydrate from potatoes instead. In other words, beans have a lower glycemic index than potatoes do.
Like potatoes, carrots have a high glycemic index. However, you’d have to eat about 4 cups of shredded carrot to get 50 grams of carbohydrate. Thus, if you ate just one carrot, it would have only a small effect on your blood sugar. To correct for this problem, some people use the glycemic load, which is the glycemic index multiplied by the total amount of carbohydrate in the food.
The glycemic index and glycemic load are of surprisingly little value to dieters. One reason is that the glycemic index of any given food is so hard to predict. For example, you could increase the glycemic index of a potato by mashing it. Then, you could decrease the glycemic index of the mashed potato by adding milk and butter. Fats and proteins tend to decrease the glycemic index of a food. Although adding butter to a food decreases the food’s glycemic index, the butter does not make the food less fattening!
Even if you eat a meal that has a high glycemic load, that doesn’t mean that your blood sugar is going to go dangerously high. It all depends on your insulin sensitivity. People who habitually eat a low-fat, starchy diet tend to have much smaller blood sugar swings than people who eat a high-fat, low-carb diet. Scientists have known that fact since the 1930s! In fact, a diet based on high-glycemic-load vegetables and unrefined starches can restore the body’s insulin sensitivity, thus curing type 2 diabetes, within a matter of weeks.
- Jenkins DJ, Wolever TM, Taylor RH et al. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr 1981;34:362-366. http://www.ajcn.org/content/34/3/362.long
Note: For more information about the control of weight and blood sugar, see my book Thin Diabetes, Fat Diabetes: Prevent Type 1, Cure Type 2.