Yet 11 obese 30-year-olds lost more weight than 12 of their peers on a conventional low-fat diet.
And they lowered their risk of heart disease.
They didn't do it with a low-carb diet, but with a slow-carb diet.
It's what nutritionists call a low-glycemic-load or a low-glycemic-index diet.
The key is eating plenty of satisfying foods that your body can't quickly convert into sugar --- slow carbs, as they're coming to be called.
"A diet focused on glycemic index may be easier to follow than diets restricted in either fat or carbs," Ludwig tells WebMD.
Foods have a higher or lower glycemic index depending on how much of them you eat, how you cook them, and what you eat them with.
---At the top --- to be eaten sparingly if at all --- come refined grains, potatoes, and sweets.
Obese participants in the study were instructed to eat nonstarchy vegetables, fruits, beans, nuts, and dairy products.
They were told to eat carbs with protein and healthful fat at every meal and snack.
After 12 months on the diets, the slow-carb group lost 7.8 percent of their body weight compared with 6.1 percent in the low-fat-diet group.
The levels were down 37 percent in the slow-carb group compared with 19 percent in the low-fat group.
The Ludwig study is far from the first to find benefits for a low-glycemic-load diet, says Jennie Brand-Miller, PhD, professor of human nutrition at the University of Sydney, Australia, and co-author of The Low GI Diet Revolution and other books in The New Glucose Revolution series.
"This study is telling us that losing weight on a low-GI diet produces better outcomes in terms of heart health than a conventional weight loss diet," Brand-Miller tells WebMD.