Raspberry ketone is a natural phenolic compound that is the primary aroma compound of red raspberries. Raspberry ketone occurs in a variety of fruits including raspberries, cranberries and blackberries. It is biosynthesized from coumaroyl-CoA. Extraction of pure raspberry ketone is usually 1–4 mg per kg of raspberries.
Since the natural abundance of raspberry ketone is very low, it is prepared industrially by a variety of methods from chemical intermediates. One of the ways this can be done is through a crossed aldol-catalytic hydrogenation. In acetone and sodium hydroxide, 4-hydroxybenzaldehyde can form the α,β-unsaturated ketone. This then goes through catalytic hydrogenation to produce raspberry ketone. This method produces a 99% yield.
Raspberry ketone is used in perfumery, in cosmetics, and as a food additive to impart a fruity odor. It is one of the most expensive natural flavor components used in the food industry. The natural compound can cost as much as $20,000 per kg. Synthetic raspberry ketone is cheaper, with estimates ranging from a couple of dollars per pound to one fifth of the cost of natural product.
Although products containing this compound are marketed for weight loss, there is no clinical evidence for this effect in humans. The average daily intake of dietary raspberry ketone has been estimated as 0.42 mg/kg/day. Early studies in rats looking into the potential toxicity of raspberry ketone found no effects on the body weight of rats with doses up to 100 mg/kg, 238 times greater than the estimated intake for humans or 0.01% of body weight. A more recent study demonstrated that when mice were fed very high doses of raspberry ketone, 2% of their diet by weight, there was a statistically significant prevention of high-fat-diet-induced elevation in body weight. The high dose effect is reported to stem from the alteration of lipid metabolism, increasing norepinephrine-induced lipolysis and fatty acid oxidation in cultured adipocytes.
Nutritional supplement manufacturer Andrew Lessman criticized and countered sensationalized media and marketing claims about raspberry ketone’s purported weight-loss benefits and strongly cautioned against its use.
Little is known about the long term safety of raspberry ketone supplements. Because it is chemically related to the stimulant synephrine, there are some concerns about its safety. Toxicological models indicate a potential for cardiotoxic effects as well as effects on reproduction and development.
In 1965, the US Food and Drug Administration classified raspberry ketone as generally recognized as safe (GRAS) for the small quantities used to flavor foods. In the UK, raspberry ketone supplements are on the Food Standards Agency’s unauthorized list.