A raspberry contains 200 molecules that contribute to its distinct raspberry flavor. One of those, raspberry ketone, was singled out by food manufacturers decades ago for its potent smell. Berry-flavored candy, soaps and candles made today likely use raspberry ketone. More recently, the raspberry ketone garnered public attention again, but this time as a purported weight-loss aid.
Raspberry ketone is actually found in cranberries, blackberries as well as red raspberries, or the species Rosaceae Rubus idaeus L. Red raspberries are native to Europe, Northern Africa and Central Asia. They have essential nutrients including beta-carotene and vitamins A, E and C. Only trace amounts of raspberry ketone are found in the fruit, so berry-flavored foods typically use raspberry ketone produced in a lab.
Around 2010, scientists noticed that raspberry ketone had a similar molecular structure to capsaicin, which is the chemical responsible for the heat in chili peppers. Preliminary studies also suggested that capsaicin prevents weight gain. In light of these findings, scientists ran studies in mice and on human tissue to see if raspberry ketone also influences weight gain.
Does raspberry ketone work?
"Reliable research on the use of raspberry ketone for any health condition in humans is currently lacking. Further high-quality research is needed," said Catherine Ulbricht, senior pharmacist at Massachusetts General Hospital in Boston and co-founder of Natural Standard Research Collaboration, which reviews evidence on herbs and supplements.
Only a handful of preliminary studies have been done to look at raspberry ketone as a weight loss aid, and none of these were done in humans. But the studies on mice or cells have signaled a potential weight loss effect. A 2005 study on mice fed a high-fat diet found raspberry ketone prevented weight gain in the liver, and gains of visceral fat ("belly fat") that surrounds organs, according to the paper in the journal Life Sciences.
Another study showed raspberry ketone increased the breakdown of lipids (fat molecules) within fat cells. The 2010 paper in the journal Planta Medica also found raspberry ketone spurred fat cells to secrete more of the protein adiponectin. Low levels of adiponectin in the body are more common among people who are obese, and those with type 2 diabetes.
A 2016 study presented at the Experimental Biology conference found that mice that were fed a high-fat diet gained less weight if they were also fed raspberry ketone along with ellagic acid, another molecule found in raspberries. That study also found that raspberry ketone altered the expression of genes in the liver in a manner that appeared favorable to the mice's health.
However, a 2017 study conducted by researchers in Denmark suggested that raspberry ketone itself may not reduce body fat levels. In that study, published in the journal Food & Function, researchers found that mice fed a high-fat diet and raspberry ketone gained less weight compared with mice not given raspberry ketone. But the raspberry ketone-fed mice also didn't eat as much food as mice that weren't fed this molecule, and the researchers concluded that raspberry ketone did not reduce fat levels beyond what would be expected from a lower calorie diet.
Preliminary research has also found that raspberry ketone – when applied directly on the skin – could help combat signs of aging. A 2008 study of 15 people found applications of raspberry ketone improved both skin elasticity and hair growth over five months, according to the study in the journal Growth Hormone & IGF Research.
Research in mice, and on cells growing in lab dishes, often inspires more research. But for results that can be trusted, doctors look for many human trials of a chemical, with many participants. Overall, the U.S. Department of Defense Human Performance Resource Center deems the weight loss evidence on raspberry ketone as "insufficient." The Natural Standard Research Collaboration Natural graded raspberry ketone as a "C" for evidence supporting claims for any health benefit.
Is raspberry ketone safe?
The U.S. Food and Drug Administration first categorized raspberry ketones as a "Generally Recognized as Safe" (GRAS) food additive in the 1960s. However GRAS status is given under the assumption that a person will consume less than two milligrams of raspberry ketone a day. Most weight loss supplements pack far more raspberry ketone into their products.
Raspberry ketone is not well studied at concentrations used in supplements – which can range from 50 to 250 milligram per serving. And there are some known side effects from their use.
"Raspberry ketone may lower blood sugar levels, and decrease the risk of bleeding," Ulbricht said. So, people taking drugs for diabetes should be monitored closely by their healthcare team. Raspberry ketone may also cause changes in body fat and weight, changes in inflammation, heart palpitations and shakiness. Raspberry ketone may also interact with medicines, such as those that regulate heart rate and cholesterol, and hormones.
"There is currently not enough reliable safety information on the use of raspberry ketone in humans," Ulbricht said.
In a 2015 study, published in the journal Regulatory Toxicology and Pharmacology, researchers in Denmark used a model to look at the potential effects of raspberry ketone on the human body. Their findings suggested that raspberry ketone could have potentially toxic effects on the heart, as well as effects on the reproductive system. "The compound's toxic potential should be clarified with further experimental studies," the researchers said.
Editor's Note: This reference article was first published Sept. 26, 2013 and was updated with newer information on June 23, 2017.