Something doesn’t add up in the NPR article. The sidebar of the article says, “The makeup of the low-carb group’s diet was: 28 percent carbs; 40 to 43 percent fat; about 28 percent protein.”
But the abstract of the study in the Annals of Internal Medicine (cited in the NPR article) describes the group’s diet as “low-carbohydrate (<40 g/d).”
So a couple thoughts on this:
Consuming less than 40g per day of carbs is not merely low-carb, but VERY low-carb, low enough to put the body in ketosis. Ketosis is a recognized, effective mechanism for weight loss (e.g. Atkins Diet), but not feasible for most people to keep up as an ongoing nutritional lifestyle;
If the low-carb group ate less than 40g of carbs per day (as the Annals abstract says), and calories from carbs were 28% of the diet (as the NPR article says), then that represents a total caloric intake of only 571 calories or less per day! A VERY low-calorie diet, in fact a starvation diet. If the low-carb group kept that up for 12 months, they’d have lost a lot more than 12 pounds apiece. (The NPR article says the low-carb group lost 12 pounds, but the abstract in the Annals said they lost 3.5kg, which is more like 8 pounds.)
It seems to me that the NPR article got its wires crossed somewhere. If the “low-carb” group ate less than 40g of carbs per day for 12 months, they were following a ketogenic diet, which has been recognized for decades to be conducive to weight loss. If the participants were eating 1500 calories per day (neither source says how many total calories per day they were eating, but it seems unlikely that such a study would involve fewer calories than that), their diet was more like 11% of calories from carbs.
Beyond the above points, I suspect it’s highly likely that the test participants mis-reported their true food intake, as patients often do.