California ? Diet not working? Blame your genes. That’s the pitch behind a new test that claims to show whether people will do better on a low-fat or a low-carb weight loss plan.

We’re all hard-wired with DNA that controls how we burn and store calories from various foods, and the test claims to sort out this machinery. A study this week found that women on diets well-matched to their genes, as defined by the test, lost roughly five times more weight than those on mismatched diets.

“We were able to explain why some people were successful” and others were not, even though they ate the same way, said Mindy Dopler Nelson, a nutritional biologist at Stanford University who led the study but has no financial ties to the maker of the test.

Some scientists find this hard to swallow. It’s another test being peddled without enough research to show it really works, they say.