If you believe the hype - and there's been plenty of it - ketones, which are now in all sorts of weight loss products, speed up your metabolism so your body burns away the fat.
David Schardt, senior nutritionist with the Center for Science in the Public Interest, says there's no proof raspberry ketone does anything.
"There's no evidence in humans, it's never been studied in humans that it will cause you to lose any weight. There's really one small animal study and there the results were ambiguous, so there's really no evidence that raspberry ketones will do anything for you."
Schardt also reminds us that despite the claims, no supplement can burn away the fat or target fat in specific areas, such as the belly.
"They may boost your metabolic rate slightly for short periods of time, but the evidence is that over the long period there is no effect on body weight from these fat burners."
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