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.
Miller says the study makes it clear that high-saturated fat diets are pro-inflammatory and that they promote heart disease in other ways as well.
But a spokeswoman for Atkins Nutritionals says the eating plan the study participants followed in no way resembles what is recommended for weight maintenance.
In an email exchange with WebMD, Atkins Vice President of Nutrition and Education Colette Heimowitz, MSc, says that on the maintenance phase of the Atkins diet, fat should make up no more than 40% of total calories, and no more than 10% of calories should come from saturated fat.
The study participants typically ate about three times as much saturated fat as they should have if they were following Atkins for weight maintenance, she says.
Heimowitz says that Atkins dieters consistently show improvements in blood fats, or lipids, in the form of decreased triglycerides. But this improvement was not seen in the study participants while they were on the low-carbohydrate, high-fat diet.
“Whatever diet Dr. Miller used, it was not ‘Atkins’, and the lipid response he reported is what one might expect to result from a rich mixture of carbohydrates and fat and overfeeding to avoid weight loss,” she notes.
She says three decades of research has shown the Atkins diet to be safe, and that the study by Miller and colleagues was too small and too short to allow for meaningful conclusions.
“The final sample size was 18, yet they make generalizations to many people,” she says. “The entire duration of the treatment was four weeks, yet they make statements about ‘long-term maintenance.’”
Ornish Weighs In
Miller acknowledges that the maintenance phase of the Atkins diet is not very different from the typical Western diet.
But he says many people stay on the more extreme, early phase of the diet, which is much higher in saturated fats, long after weight loss is no longer a goal.
“The main message is that reducing the saturated fat in the diet is better for overall heart health,” he says.
Low-fat diet proponent Dean Ornish, MD, tells WebMD that the study by Miller and colleagues explores the impact of high saturated-fat diets in a unique way.
He cites a separate study, published last week in the journal Archives of Internal Medicine, finding that older people who eat large amounts of saturated fat in the form of red and processed meat are more likely to die of heart disease and cancer.
He says the two studies “directly contradict” the idea that all diets are equally healthy as long as they promote weight loss.
Ornish is founder and president of the Preventive Medicine Research Institute in Sausalito, Calif.
The American Heart Association (AHA) recommends that no more than 35% of total daily calories come from fat, and no more than 7% of calories come from saturated fat sources.
Nutritionist Alice Lichtenstein, DSc, who is an AHA spokeswoman, says protein should come primarily from low-fat sources like fish, legumes, and lean meat. Dairy foods should be low-fat or nonfat, and, of course, eating plenty of fruits and vegetables is important.
Lichtenstein is a professor of nutrition science and policy. She directs the Cardiovascular Nutrition Laboratory at Tuft's University's Jean Mayer USDA Human Nutrition Research Center in Boston.
“If you follow this pattern, you will end up with a diet that is in line with what AHA recommends,” she says.