At a time when Americans are getting heavier and are searching for diets that will help them shed more pounds, a major study published in the New England Journal of Medicine today offers long-awaited answers.
The study is the latest round in the ongoing diet wars between the low-fat and low-carb diet rivals.
Low-fat diets are endorsed by the American Heart Association and emphasize grains, whole wheat pasta and bread, fruits and vegetables.
Its competitor: the low-carbohydrate diet, which emphasizes meat, fish, chicken, eggs, and just a few vegetables.
Dr. Meir Stampfer, the study's senior author and professor of epidemiology and nutrition at Harvard School of Public Health, told ABC News: "The low-carb diet was the clear winner in providing the most weight loss."
The study, conducted at Brigham and Women's Hospital in Boston and Ben Gurion University in Beer Sheba, Israel, followed 322 obese patients who were randomly assigned to a low-fat diet, a low-carb diet or a third eating plan, a Mediterranean diet, which includes lean protein and vegetables, along with lots of olive oil and nuts.
After two years, the longest follow-up of any diet study to date, the diets varied in terms of weight loss results.
While low-fat dieters lost an average of 7.3 pounds over the two-year period, those following the Mediterranean diet shed 10.1 pounds. The low-carb dieters peeled off the most weight, losing an average of 12.1 pounds.
"The low-carb diet makes you feel fuller and it's more satiating, so you're not as hungry," Stampfer said. "That means it's easier to stick to that diet long term."
And perhaps the most surprising: people on the low-carb diet, even after two years of dining on meat and cheeses and eggs, did not have increased cholesterol levels. In fact, it actually lowered the cholesterol numbers of study participants.
"A low-carb diet, by giving up pasta, and bread, and potatoes, lowers insulin levels in the body," Dr. Eric Westman of Duke University said. "And when there's less insulin, the body produces less harmful cholesterol."
Research also showed that Mediterranean dieters were most likely to improve their blood sugar levels.
The findings knock low-fat diets out of the top spot and raise the question: Should everybody follow a low-carb diet? And would everyone want to?
To many Americans, giving up bread and pasta and potatoes is no easy task.
Researchers are quick to point out, however, that different diets work for different people. And that the most effective one, ultimately, is the one that best works for you.
But, with Americans expected to spend more than $64 billion this year trying to lose weight, these latest results give clear guidance on where to start.