Some participants kept a low-carb diet, in which carbs were initially limited to fewer than 20 grams per day. Other participants kept a low-fat diet, in which fewer than 30 % of calories come from fat, and total calories were reduced by 500 to 1,000 per day.
After six months patients on the low-carb diet lost more than 20 pounds, while those on the low-fat diet lost just over 10 pounds. In addition, people on the low-carb diet had lower levels of the fat triglyceride, usually associated with higher risk or heart disease and stroke. They also had higher HDL or good cholesterol, levels. Levels of LDL, or bad cholesterol, were roughly the same in each group.
The second study used similar low-carb and low-fat diets, but included obese patients with diabetes or metabolic syndrome. Patients followed the diets for one year and had the same beneficial results as the first study. The year-long study also found superior weight loss at six months in the low-carb group.
By one year the low-fat and low-carb groups weighed about the same. But the low-carb dieters still had lower triglyceride and higher HDL levels than the low-fat dieters. For those with diabetes, measures of blood sugar were significantly better in the low-carb group compared to the low-fat group.
"Patients on the low-carb diet had better outcomes" than those on low-fat diets, says Linda Stern, author of the year-long study and general internist at Philadelphia VA Medical Center.
Most diet and nutrition experts seem reluctant to embrace low-carb weight loss plans due to concerns over years of data linking high-fat diets to increased risk of heart disease and cancer.
"Low carb diets are not healthy," maintains nutrition expert Carla Wolper of the Obesity Research Center at St. Luke's Hospital in New York. "[They] increase cancer risk, and ultimately become too rigid and unpleasant to live with."
Some diet and nutrition experts are skeptical the benefits seen in the two latest studies would persist if people were followed longer than a year.
Even Frederick F. Samaha, author of the second study and chief of cardiology at the VA Medical Center in Philadelphia, agrees the low-carbohydrate diet may not have continued success after one year.
"Patients on the low fat diet continued to slowly lose weight while the low-carb group gained a little weight," notes Samaha. "The low-carbohydrate diet may not be as sustainable."
Some nutritionists believe the sooner low-carb craze is over, the better.
"I do not feel this topic should be studied at all," says David Katz, clinical professor of public health and medicine at Yale University in New Haven, Conn.
Katz believes research has already proven which diet is best — high fiber, low fat, plenty of fruits and vegetables.
"We have ample evidence of what basic dietary pattern prevents heart disease, cancer, diabetes, premature death, and obesity," Katz claims. "We should be devoting all of our resources and effort to making that pattern more accessible to people."
Yet some doctors are re-evaluating their stance on low-carb diets.
"These studies are interesting and support what we have seen in clinical practice," says Neil Brooks, a primary care physician in Vernon, Conn. "Patients lose weight more easily with low carbohydrate diets and seem to maintain the weight loss better."
Thomas Schwenk, a primary care doctor in the University of Michigan Health System in Ann Arbor, notes, "All low-carb diet studies have shown beneficial effects on lipids, so it's not clear there is a heart-unhealthy low carb diet. It is hard to eat low-carb and low-fat but it doesn't seem to matter — as long as you are losing weight, your lipids improve."
"If you are overweight," Samaha explains, "you are probably over-consuming carbohydrates. So it is not surprising that cutting carbohydrate calories out produces weight loss."
Calories Still Play a Vital Role
But Stern wonders whether some diet and nutritionists who object to the "high fat, low-carb diet" might be getting fooled by a numbers game.
"Imagine you are eating 2500 calories per day with 500 of those calories from fat," Stern explains. "You would be getting just 25 % of your energy from fat, which is well within the government recommendations of under 30 %."
Cutting out 1500 calories from carbohydrate would leave you with a 1000 calorie diet, 500 of those calories from fat.
"Fifty % fat!" Stern says. "That sounds horrible. But in reality, it's the same total amount of fat you were eating before."
In Stern's study, patients on the low-carb diet were eating less fat at one year than they had been before the study began.
You can't eat low carbs and eat a lot of fat," explains Stern.
Stern notes that low-carb is not a magic bullet: "Calories always matter. You can't eat and eat on low-carb and expect to lose weight."
The key, Stern believes, is that high-protein calories are more satisfying and so people eat fewer of them.
Source: ABC News