How the Atkins Diet Fares in Cholesterol

April 1, 2009 -- People who follow a low-carbohydrate, high-fat diet for weight maintenance, even for as little as a month, may worsen risk factors for heart disease compared to two other popular diets, a newly published study shows. 

Researchers set out to compare the impact of the Atkins, South Beach, and Ornish diets on measurable risk factors for heart disease in people who were not overweight and were not trying to lose weight. 

The idea was to examine the effects of the diets when they are used for weight maintenance and not weight loss.

Earlier this year, a widely reported study found that for weight loss, restricting calories is the key and that it matters little whether you count carbs, fat, or protein. 

But the newly published research suggests that there are big differences in the diets in terms of effects on cardiovascular risk factors when followed by people who aren’t losing weight. 

“If you are losing weight on a diet, that is probably beneficial for your health no matter which of these diets you follow,” lead researcher Michael Miller, MD, tells WebMD. “The question is, ‘Once someone has established a weight they are comfortable with, does it matter which diet they follow?’ And it appears that it does.”

Atkins, South Beach, and Ornish

The study included 18 healthy adults who were not overweight, who followed each of the three diets for one month, followed by a one-month "wash-out" period in which they ate normally. Caloric intake was increased during any phase of the study if a participant began to lose weight.

 The low-carbohydrate, high-fat diet designed to approximate the first, and most extreme, phase of the Atkins diet included 50% of calories from fat and 22% to 38% of calories from saturated fat sources like meat, cheese, and other whole-fat dairy products, Miller tells WebMD.

During their month on the Mediterranean-based South Beach diet, study participants ate 30% of calories in the form of fat, but olive and other vegetable oils, nuts, lean meats, and fish were the main fat sources. 

While on the low-fat, high-carbohydrate Ornish diet, 10% of calories came from fat. 

The researchers conducted blood tests throughout the study to assess risk factors for heart disease, including LDL (bad) cholesterol, triglycerides, and C-reactive protein, which is a measure of inflammation in the body. 

They also used ultrasound to study changes in blood vessels' flexibility -- specifically, their ability to widen to accommodate blood flow. Atherosclerosis, the hardening of the arteries, hinders that process and is associated with heart attack and stroke risk. 

The study revealed that: 

• While on the low-carb, high-fat diet, LDL cholesterol levels increased slightly, compared to decreases of about 12% and 17% respectively, during the South Beach and Ornish phases of the study. 
• After a month on the Atkins-like diet, study participants showed less blood vessel flexibility than they did after a month on the Ornish diet.   
• CRP levels remained in the normal range with all three diets, but levels went down slightly while participants were on the South Beach and Ornish diets and they went up slightly on the high-fat, low-carb diet, Miller tells WebMD. 

The study appears in the April issue of the Journal of the American Dietetic Association.