The use of raspberry ketone for weight loss has produced a lot of talk following an endorsement by television host Dr. Oz as a "fat-burner in a bottle." The Dr. Oz Show Website recommends raspberry ketones "paired with regular exercise and a well-balanced diet," but sales of "the number one miracle in a bottle to burn your fat" have soared, unlike sales of fruits and vegetables.
Raspberry ketone, also known as rheosmin, and chemically as 4-(4'-hydroxyphenyl)-2-butanone, has been known as a flavoring agent since the 1920s and is used for its fragrance in cosmetics and as an insect attractant. Raspberry ketone is one of the most expensive flavoring agents in the food industry ($20,000/kg). Of note, natural raspberry ketone is not extracted from raspberries, which have very low raspberry ketone content. Natural sources include peaches, grapes, apples, rhubarb, and the bark of trees such as yew, maple, and pine. Raspberry ketone can also be synthesized chemically, but this product cannot be labeled as a natural flavor. Additionally, "natural" raspberry ketone is produced via microbial synthesis.
Raspberry ketone is structurally similar to synephrine and capsaicin. Synephrine, a sympathomimetic, is used in dietary supplements for weight loss to replace ephedrine, which was banned by the US Food and Drug Administration because of cardiovascular toxicity. Capsaicin is a component of cayenne pepper and is used topically for myalgia and sold under a number of names. Capsaicin also has sympathomimetic activity and has generated sporadic reports of cardiovascular toxicity.
Research on raspberry ketone is scant. A MEDLINE search generated 3 studies of raspberry ketone for weight loss: 2 in rodents and 1 in vitro with no human studies. A study in mice fed a high-fat diet and raspberry ketone (2% of total diet) showed that raspberry ketone prevented weight gain and elevation of liver and adipose tissue weight, which the authors attributed to increased norepinephrine-induced lipolysis in white adipocytes. A study conducted decades earlier reported no effects on the body weight of rats given raspberry ketone 100 mg/kg, a dose up to 200 times greater than the estimated dietary intake in humans. In vitro research suggests that raspberry ketone might increase secretion of adiponectin, which is involved in lipid and glucose metabolism and in body weight.
Other animal and in vitro research suggests that raspberry ketone may protect against nonalcoholic steatohepatitis, increase skin insulin-like growth factor-1 (which is involved in promoting hair growth and increasing skin elasticity), and possess antiandrogenic, anti-inflammatory, antimelanogenic (skin lightening) activity. Very preliminary research in humans (< 15 subjects) suggests that topical application of raspberry ketone might increase hair growth in patients with alopecia and increase skin elasticity.
The safety of oral raspberry ketone in humans is unknown. Given the chemical similarity of raspberry ketone to synephrine and capsaicin, patients with conditions that increase the risk for cardiovascular adverse events, such as hypertension, should avoid raspberry ketone. Without research in humans on the efficacy and safety of raspberry ketone for weight loss, raspberry ketone should not be recommended. Advise patients to instead heed the other 2 parts of Dr. Oz's recommendation -- regular exercise and a well-balanced diet.
Gayle Nicholas Scott, PharmD