THE low-carb, high-fat Atkins diet gets high marks in one of the biggest, longest head-to-head studies of popular weight-loss plans, beating the Zone, the Ornish diet and even U.S. guidelines. Even so, critics say the results show how hard it is to lose weight and keep it off.

Overweight women on the Atkins plan lost more weight over a year than those on the low-carb Zone diet. And they had slightly better blood pressure and cholesterol readings than those on the Zone; the very low-fat, high-carb Ornish diet, and a low-fat, high-carb diet similar to U.S. government guidelines.

Stanford University researcher Christopher Gardner, the lead author, said the study shows that Atkins may be more healthful than critics contend.

But the study isn’t a fair comparison because by the end, few women were following any of the diets very strictly, critics argue, although those in the Atkins group came the closest.

The study “had a good concept and incredibly pathetic execution,” said Zone diet creator Barry Sears.

“It’s a lot easier to follow a diet that tells you to eat bacon and Brie than to eat predominantly fruits and vegetables,” said Dr. Dean Ornish, creator of the Ornish diet.

Atkins followers lost about 4.5 kilograms on average at 12 months, versus 1.6 kilograms for the Zone dieters.

Women on the Ornish diet lost almost 2.25 kilograms on average and those on the national guidelines plan lost almost 2.72 kilograms.

Scientifically, those 12-month results weren’t different enough from the Atkins weight loss to rule out the possibility that the differences occurred by chance.

The dieters lost the most weight early on, including an average of 5.9 kilograms for the Atkins group at six months — nearly double the closest competitor, the national guidelines diet. After that, most began regaining weight, a trend most noticeable in the Atkins women.

“There’s not a ton of weight loss here,” Gardner acknowledged. Atkins “isn’t the solution for the obesity problem,” he said.

The study involved 311 women about 40 years old on average and was designed to measure the effectiveness of using a diet book to lose weight.

Women were randomly assigned to read one of four diet books. They attended weekly classes for eight weeks where diet questions were addressed, but then were mostly on their own for the next 10 months.

Ornish and other naysayers argued that the study doesn’t answer a big question about the Atkins diet — whether consistently eating all that fatty food long-term leads to health problems.

The study appears in Wednesday’s Journal of the American Medical Association.