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Many physicians and nutritionists still have concerns that high-protein, low-carbohydrate diets may have adverse long-term health effects. However, scientific data to support these concerns is lacking.
"I don't believe that there is enough data to determine whether a link exists between [heart disease and] low-carbohydrate, high-protein diets in otherwise healthy persons, " said Dr. Peter Schulman of the University of Connecticut School of Medicine.
The Atkins Diet, one of the most popular diets in the United States, has been shown to both reduce weight and lower cholesterol. Yet physicians have been hesitant to recommend Atkins-type diets because of concerns that high fat content may lead to an increased risk of heart disease.
"In my experience, unless you're willing to throw out decades of research, you cannot ignore that diets chronically high in saturated fats are linked to heart disease," said Dr. Keith-Thomas Ayoob of Albert Einstein College of Medicine in New York. Ayoob is also a spokesman for the American Dietetic Association.
The Missing Link
The latest controversy involving Atkins-type diets arose today as the Physician's Committee for Responsible Medicine held a news conference calling for an investigation of the potential harmful effects and deaths that may be associated with these diets. The organization compiled the results of an online survey of Atkins-type diet participants who complained of adverse effects they attribute to the diet.
However, many experts say that conclusion about Atkins-type diets and possible adverse reactions cannot be drawn from the data presented by the PCRM.
"The study ... does not appear to be randomized. Theoretically, if the people who elected to go on a low-carb diet were different somehow -- sicker, for example, and more willing to try something else -- that could explain the results," said Dr. Donald Hensrud, professor of preventive medicine and nutrition at Mayo Medical School in Rochester, Minn.
Critics of the PCRM's data maintain the problem with these types of studies is that the authors cannot prove a cause-and-effect relationship between these diets and adverse effects.
Long-Term Studies Needed
What, then, are the best kind of studies too evaluate the safety of Atkins-type diets? Experts say randomized, long-term studies will be the most informative.
"Most of these diets are used by individuals for short times. The impact of any short-term intervention on heart disease is negligible. An important question is what happens for the long term," said Dr. Arthur Frank, director of the George Washington University Weight Management Clinic in Washington, D.C.
"I'd like to see a long-term study of at least 18 months, preferably two years, good compliance and follow-up to see what happens," said Ayoob.
These studies would monitor weight and cholesterol and track patients for adverse reactions such as heart disease and kidney problems.
Eat Fat and Cholesterol Gets Better?
Two short-term studies published in the New England Journal of Medicine this year found that cholesterol levels were reduced in obese patients on high-protein, low-carbohydrate diets.
"The surprise in the studies last year of Atkins was not that there was weight lost; it was that the lipid [cholesterol] profiles of the patients got better, not worse as people had predicted," said Dr. Paul Shekelle, a professor at University of California, Los Angeles, School of Medicine and director of the Southern California Evidence-Based Practice Center.
"I have seen the same thing in clinical practice. The presumption is that the loss in weight, which will improve the lipid profile, is more than counterbalancing any adverse effect [of] the high-protein diet," said Shekelle.
Scientists have wondered if these diets could have a negative effect on the heart even though they may improve HDL, which is also known as "good" cholesterol.
"The real question here is what happens when weight loss stops, and a patient continues on some version of the diet," Shekelle said. "I would think there is a real danger of an adverse effect on lipids and, if sustained, an adverse effect on the heart. I think the likelihood of an adverse effect on the heart is small when HDL and triglycerides are declining."
Dr. David Katz, director of the Yale Prevention Research Center in Derby, Conn., is concerned that diets high in animal fat and protein are associated with problems with blood flow, blood clots and inflammation, which lead to heart disease.
"It is altogether incorrect to think of cholesterol as an overall measure of health, or even cardiac risk. Look at the recent trial results with hormone replacement therapy. Even though hormone replacement therapy improves lipids, it does not improve cardiac risk and may increase it," said Katz, author of the book The Way to Eat .
It's All About Choice
Laurie Tansman, nutrition coordinator at Mount Sinai Hospital in New York, said that while she "not an advocate of an extreme diet such as the Atkins Diet, it all depends on the choices made."
"You could be on the Atkins Diet and choose low-saturated-fat choices such as reduced-fat cheeses, skinless light-meat chicken and turkey, fish as well as lean cuts of beef, lamb, pork and veal. And, you can choose heart healthy fats such as olive oil," she said.
Tansman agrees that reducing carbohydrates will likely lead to weight loss and better cholesterol levels. "But you do not need to go on such an extreme diet to make such improvements," she added.
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