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Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Barbara K. Hecht, PhD

It is the type, rather than the amount, of carbohydrates in your diet that helps determine your body weight, according to scientific studies. Nutrition researchers studied the height and weight of 572 healthy people in Massachusetts and asked them to report their weekly intake of carbohydrates during a one-year period. They found that overweight people ate more refined ("bad") carbohydrates than those who weigh less.

Refined carbohydrates are, for example, those found in sugar, white breads, pasta, crackers, and cereals. Refined carbohydrates are "bad" because they have what is called a high glycemic index, meaning that these foods cause a sudden and sharp increase in blood sugar. If this blood sugar is not used by the body, it is stored as fat.

Processed foods, by definition, contain high amounts of refined carbohydrates. During processing, nutrients and fiber are often removed from these foods. Since fiber helps slow the release of sugar into the blood, the loss of fiber is one reason that processed foods have a high glycemic index.

Whole grains, vegetables, and fruits also contain carbohydrates, but these carbohydrates are "good" ones because they have a lower glycemic index.

In the Massachusetts study, neither the total amount of carbohydrates nor the proportion of calories derived from carbohydrates correlated with the body mass index (BMI), a key measure of weight that takes height into account. But people with a high BMI ate more of the refined, high-glycemic-index carbohydrates than their slimmer peers.

This report, along with other evidence, suggests that carbohydrates can be part of a successful weight-loss program, provided that carbohydrate consumption is limited to "good" carbs -- the carbs found in breads, crackers, pastas, and cereals made with whole wheat, along with fruits and vegetables.

Reference: Ma Y, Olendzki B, Chiriboga D, Hebert JR, Li Y, Li W, Campbell M, Gendreau K, Ockene IS. Association Between Dietary Carbohydrates and Body Weight. Am J Epidemiol. 2005 Feb 15;161(4):359-67.