Feb. 11, 2004 -- Much like the controversy surrounding the health of diet guru Robert Atkins, MD, at the time of his death last April, the debate about the safety of the low-carbohydrate diet Atkins became famous for isn't likely to calm down any time soon.
Critics of low-carb approach say the high-fat content of the Atkins diet, which advocates meat, eggs, and cheese and limits bread, pasta, and fruit, raises the risk of heart disease. But low-carb devotees say the diets are safe and effective in promoting weight loss, which in turn lowers the risk of heart disease.
But researchers say the facts boil down to this: There simply isn't enough data on low-carb diets to support either argument.
"There are two extremes, but I think there is no evidence to support either extreme in terms of benefits or harmful effects of this kind of diet," says Frank Hu, MD, PhD, associate professor of nutrition and epidemiology at the Harvard School of Public Health.
Many Questions, Few Answers
The prevailing view during the last 20 years has been that a low-fat diet is the best way to achieve weight loss and reduce the risk of heart disease. But the epidemic of obesity that the U.S. is currently experiencing indicates that low-fat diets may not be the solution.
"The question now is whether the other extreme, a low-carb diet, is the answer," says Hu.
During the "induction" phase of Atkins, in which carbohydrates are most strictly limited, people typically consume as much as 60% of their calories from fat, including "bad" saturated fats from animal sources that raise cholesterol levels and "good" unsaturated fats, such as those found in olive oil and fish, which have favorable effects on cholesterol profiles.
Although the Atkins diet has never specifically prescribed recommended amounts of fat or protein, an Atkins educator recently told The New York Times that only 20% of a dieter's calories should come from saturated fat.
Hu says getting even 20% of calories from saturated fat is still too high. The American Heart Association and many other health organizations recommend a maximum intake of 10% of total calories from saturated fat in order to reduce the risk of heart disease.
"Based on what we know so far, you can expect that if you eat this kind of diet for many years, there could be harmful effects on heart disease and diabetes," says Hu. "The benefits of weight loss may outweigh the potential harmful effects of saturated fat and cholesterol within the short-term, but in the long-term we don't know."
The Evidence on Low-Carb Diets
Researchers hope studies currently underway will help answer some of those questions about the safety of low-carb diets. Until then, only short-term studies have addressed these issues.
A review of the research currently available on the safety and effectiveness of low-carb diets published last year in The Journal of the American Medical Association concluded that there was "insufficient evidence for or against the use of these diets."
"Despite the large number of Americans who have apparently adopted this approach to weight loss and/or weight maintenance, we know little of its effects or consequences," write researcher Dena Bravata, MD, of the Center for Primary Care and Outcomes Research at Stanford University and colleagues.
Some short-term studies have shown an improvement in cholesterol levels after six months on the Atkins diet. But Bravata's study showed that of the few low-carb studies that included information on cholesterol levels of the participants, there was no change in total, LDL ("bad") and HDL ("good") cholesterol levels. In contrast, the larger number of studies on higher-carbohydrate diets that included information on cholesterol levels showed a significant decline in total cholesterol levels.
Researchers say the lack of long-term data on low-carb diets severely limits their ability to evaluate their safety and effectiveness in promoting weight loss as well as reducing the risk of heart disease.
"The bottom line is that there is no single diet that is optimal for everyone," says Hu. "But if you choose the healthy sources of fats, carbohydrates, and protein, you can have many options to design a healthy diet not only for weight loss but also for the prevention heart disease and diabetes."