Millions of Americans are in the process of losing weight. Which diet works best?

Traditionally, doctors have told overweight patients to follow a low fat regimen. But a new study is questioning the practice of minimizing fat.

"Fat is an important component of any healthy diet,” said registered dietician Tara Miller.

Researchers put hundreds of obese patients on one of three diets.

"Head to head, low fat, low carb and Mediterranean diet," said Dr. Meir Stampfer from Brigham and Women’s Hospital.

The Mediterranean plan consisted of fish, fruits, vegetables and good fats from olive oil and nuts.

Low carb eaters were encouraged to consume healthy fats as well.

After two years low fat dieters lost an average of 6 and half pounds.

But those on the Mediterranean diet lost 10 pounds and low carb eaters dropped even more.

Not only did people on the Mediterranean and low carb diets lose more weight, they also had better cholesterol levels.

Experts say healthy fats make a diet easier to stick with.

"That keeps you full longer so you're less likely to overeat, you're less likely to binge between meals," Miller said.

That helped physician Stacey Wassermann lose 43 pounds.

"The healthy eating is more part of my lifestyle now than trying to diet," Wassermann said.

The study authors say no one diet works for everyone and doctors should be flexible.

"I think the first choice for weight loss should be Mediterranean style or low carb, and low fat works for some people but it shouldn't be the first choice," Stampfer said.

Eating a healthy amount of fat may help people lose it.