Nutrition - Ask a Physician
Not all carbohydrates are the same
Adrienne Youdim, MDMedical Director
Cedars-Sinai Center for Weight Loss
As a starting point, it's important to understand what constitutes a carbohydrate. Carbohydrates include foods such as rice, pasta, potatoes and pastries, but are also found in fruits, vegetables and whole grains - foods that have beneficial health effects and have been associated with a reduced rates of stroke,heart disease,diabetes, and certain cancers such as colon cancer.
Carbohydrates used to be classified as "simple" and "complex." In general, simple carbohydrates (such as table sugar) were considered harmful and complex carbohydrates (such as whole grain bread) were considered healthy. This classification is too simplistic, however, as all carbohydrates must be broken down into single sugar molecules to be digested. The quantity and quality of the carbohydrates should be considered, too - especially, the effect that these foods have on blood sugar when digested.
The glycemic index
Another way of classifying carbohydrates is the glycemic index, which measures how fast blood sugar rises after eating the carbohydrate. The glycemic index of a food is determined by the quality of the carbohydrate, including fiber content, fat content and physical form. In general, non-starchy vegetables, fruit and legumes have a low glycemic index and refined, starchy foods have high glycemic index. Diets consisting of high glycemic index foods cause large, rapid rises in blood sugar and insulin, and may increase the risk of obesity, heart disease and diabetes.
What studies have shown
The largest and longest-running study of low-carbohydrate diets was published in the March 7, 2007 issue of the Journal of the American Medical Association. Among the study's key findings were:
- Those following a low-carb regimen lost an average of 10.4 pounds after one year, compared to 5.7 pounds for those on a traditional, balanced diet based on federal nutritional guidelines. (Previous studies had shown low-carb diets producing greater weight loss than low-fat diets at six months, but negligible difference at 12 months.)
- After one year, measurements for cholesterol and levels of insulin, glucose and blood pressure for the low-carb dieters were comparable with or more favorable than the other diet groups
- While low-carb diets decreased triglycerides (TG) and increased HDL (good cholesterol), they also increased total cholesterol (TC) and LDL (the harmful cholesterol), which are associated with increased risk of heart disease.
My advice
While evidence to evaluate the long-term effects of low-carb diets is slim, we do know that low-carb diets tend to be high in saturated fat and trans fat - fats that have been associated with reduced HDL, increased LDL and increased risk of heart problems. Moreover, low-carb diets don't take into account the quality of the carbohydrate or the glycemic index, which also appear to have a role in heart disease, diabetes and obesity.
The bottom-line? Although low-carbohydrate diets appear to be a reasonable choice for short-term weight loss, a lifestyle that involves consuming large amounts of foods rich in saturated fats increases the risk of heart disease. For the long-term, limit refined sugars and starchy foods. Instead, eat plenty of fruits, vegetables and whole grain foods. These high-quality carbohydrates, which are low on the glycemic index, contain nutrients that may actually reduce the risk of heart disease and cancer
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