Raspberry ketones (RK) are the chemical compounds that give raspberries their enticing aroma. When ketones are extracted from raspberries, they can be used to add fragrance, flavour or colouring to things like fizzy drinks, ice cream and cosmetics.
However, what put raspberry ketones in the spotlight were unproven claims that raspberry ketone supplements could help melt away fat and prevent weight gain, even despite a high-fat diet.
Raspberry ketones supplements can no longer be sold legally in the UK. In 2014, the Food Standards Agency ruled that raspberry ketones were an unauthorised 'novel food'.
Raspberry ketones flavourings are still permitted.
What the science says
There have been no human studies so far on the weight loss effects of raspberry ketones.
The only research on the effect of raspberry ketones on fat are a handful of animal studies. The studies were done over the last 10 to 15 years. Researchers looked at the effect of raspberry ketones on rats, mice and rabbits.
One 2005 Japanese study looked into the effects of raspberry ketones on obese male mice fed a high fat diet. They wanted to see if these compounds could prevent obesity and reduce overall body fat and visceral fat stored around organs. One of the results of this study concluded that the addition of raspberry ketone helped:
- Reduce body weight by speeding up processing of fat
- Reduce fatty tissue, especially liver fat stores
However, this was a small study of six mice and the same effects have not been tested or observed in humans.
A Korean study carried out in 2010 took a closer look at the way raspberry ketones may work to prevent obesity. Researchers concluded that by stimulating lipolysis (the breakdown of fats) and other chemical processes, raspberry ketones suppress fat accumulation and improve fat metabolism. In this case, the effects of raspberry ketones were documented but the underlying mechanism of how this worked was not confirmed. Also, the research conducted only involved isolated cells in test tubes. There is no way to know whether the same results would be produced in people.
The unknown potential for harm
Raspberry ketones in food and cosmetics are generally considered safe but no one knows what short or long-term effect raspberry ketone supplements could have on your overall health. That's because there has been no study to document potential side effects. There are also no studies that look at potential drug or food interactions.
The fact that the chemical make-up of raspberry ketones is similar to other stimulants does suggest the potential for certain side effects and there are anecdotal reports of jitteriness, increased blood pressure and rapid heartbeat among people taking raspberry ketone supplements. However, without the evidence, no one can say what dosage of raspberry ketone supplements, if any, might be safe to take.
For now, the best advice is to discuss your concerns about weight and weight management with your GP or nurse before trying any unproven method to control your weight.