Blueberries a fat-fighter? Not so fast.

Blueberries may combat obesity—at least, perhaps, in rat cells, according to research presented at the American Society for Nutrition conference Sunday.

Blueberries are already considered health food champions— they’re a favorite of dieters and may be linked to a reduced risk of diabetes and high blood pressure.

A researcher from Texas Woman’s University wanted to know whether compounds in blueberries called polyphenols —which have been shown to stop fat cell development in other studies—would also fight obesity. Shiwani Moghe, a graduate student, applied polyphenols from blueberries onto rat tissue samples to see if it would stop some cells from turning into fat storage cells.

Indeed, the fat shrank. Moghe found that the highest dose of polyphenols she used reduced the lipid content (fatty molecules) in the tissues by 73%; the lowest dose reduced fatty content by 27%. She presented her research on Sunday in Washington, D.C.

But a quick reality check: This wasn’t a study that tracked people eating blueberries over several months. This was a lab study, using rat tissue, not human tissue. And the tissue wasn’t getting tested with every compound in blueberries, just a dose of a particular compound (polyphenols are also found in onions, apples and red wine).

Blueberries won’t hurt you, but there’s no evidence yet that eating them will help you burn fat. And just so you know, grapefruits aren’t proven to burn fat either.

At this point, it’s probably just simpler – and a lot smarter – to cut out the Cheetos and second helpings of dinner.