Research on low-carbohydrate diets has yet to produce a conclusive medical recommendation. Scientific literature supplies material that affirms advocates and opponents, although the preponderance of evidence doesn't support low-carb diets.
The Journal of the American Medical Association, for instance, last April published a review of more than 30 years of relatively short-term studies of low-carbohydrate diets.
Low-carb advocates like to talk about how the report seems to answer the criticism that the relatively high-fat regimen poses a risk of cardiovascular disease. The JAMA review of studies involving 3,268 people showed that these diets did not raise blood lipids associated with harmful cholesterol, which has in turn been linked to heart disease.
Skeptics note this review considered only studies of diets that lasted a year or less. They also point to the part of the report saying that weight loss on these low-carbohydrate diets appeared to have more to do with calories than carbs.
In part, the low-carb argument says carbohydrates - particularly sugar, white rice and refined flour - spike insulin, leading to weight gain by causing fat storage or simply by making you hungry. This theory has not been confirmed in research.
In their conclusion, the seven JAMA authors find "insufficient evidence to make recommendations for or against the use of low-carbohydrate diets."
Hundreds of studies of low-carbohydrate diets have been conducted, but there has yet to be a study showing the diet's long-term effects. Critics say the diet lacks health benefits that may come from eating a diet rich in fruit, vegetables and whole grains.
In its most recent recommendations of 2002, the National Institutes of Health recommends that children and adults eat at least 130 grams of carbohydrates a day to "produce enough glucose for the brain to function." The low-carbohydrate diet can vary from 20 daily grams of carbohydrates in its most extreme form to about 100.
Low-carbohydrate advocates tend to view such government advice as hopelessly stuck in outmoded "food guide pyramid" thinking. Since 1992, the pyramid has recommended a diet rich in carbohydrates without necessarily differentiating between the more healthful ones - whole grains, fruit, vegetables - and those that are less so.