If you need to lose weight, you are not alone.
More than a third of Americans are overweight — and another third are obese ().
Only 30% of people are at a healthy weight.
The problem is, conventional weight loss methods are so difficult that an estimated 85% of people do not succeed (2).
However, many products are advertised to aid weight loss. Certain herbs, shakes and pills are supposed to help you burn fat or reduce your appetite.
Among the most popular is a supplement called raspberry ketones.
Raspberry ketones are claimed to cause the fat within cells to be broken down more effectively, helping your body burn fat faster. They are also claimed to increase levels of adiponectin, a hormone that helps to regulate metabolism.
This article examines the research behind raspberry ketones.
Raspberry ketone is a natural substance that gives red raspberries their powerful aroma.
This substance is also found in small amounts in other fruits and berries, such as blackberries, cranberries and kiwis.
It has a long history of use in cosmetics and has been added to soft drinks, ice cream and other processed foods as a flavoring.
As such, most people already eat small amounts of raspberry ketones — either from fruit or as a flavoring ().
Only recently did they became popular as a weight loss supplement.
Even though the word "raspberry" may appeal to people, the supplement is not derived from raspberries.
Extracting raspberry ketones from raspberries is extraordinarily expensive because you need 90 pounds (41 kg) of raspberries to get a single dose.
In fact, 2.2 pounds (1 kg) of whole raspberries only contains 1–4 mg of raspberry ketones. That's 0.0001–0.0004% of the total weight.
The appeal of this product is also due to the word "ketone," associated with low-carb diets — which force your body to burn fat and elevate blood levels of ketones.
However, raspberry ketones have absolutely nothing to do with low-carb diets and will not have the same effects on your body.
Summary Raspberry ketone is the compound that gives raspberries their strong aroma and flavor. A synthetic version of it is used in cosmetics, processed foods and weight loss supplements.
The molecular structure of ketones is very similar to two other molecules, capsaicin — found in chili pepper — and the stimulant synephrine.
Studies indicate that these molecules can boost metabolism. Therefore, researchers speculated that raspberry ketones could have the same effect (, ).
In test-tube studies of fat cells in mice, raspberry ketones ():
- Increased fat breakdown — primarily by making the cells more susceptible to the fat-burning hormone norepinephrine.
- Increased release of the hormone adiponectin.
Adiponectin is released by fat cells and may play a role in regulating metabolism and blood sugar levels.
People with normal weight have much higher levels of adiponectin than those who are overweight. Levels of this hormone increase when people lose weight (, ).
Therefore, it seems that raising adiponectin levels could help people lose weight and lower the risk of many diseases.
However, even if raspberry ketones raise adiponectin in isolated fat cells from mice, this does not mean that the same effect will occur in a living organism.
Keep in mind that there are natural ways to increase adiponectin that do not involve raspberry ketones.
Summary Raspberry ketones have a similar molecular structure as two known fat-burning compounds. While they show potential in test-tube studies, these results do not necessarily apply to humans.
Raspberry ketone supplements exhibit promise in studies on mice and rats.
However, the results weren't nearly as impressive as the supplement manufacturers would have you believe.
In one study, raspberry ketones were given to some mice fed a fattening diet ().
The mice in the raspberry ketone group weighed 50 grams at the end of the study, while the mice that didn't get ketones weighed 55 grams — a 10% difference.
Note that the mice fed ketones did not lose weight — they just gained less than others.
In another study in 40 rats, raspberry ketones increased adiponectin levels and protected against fatty liver disease ().
However, the study used excessive dosages.
You would have to take 100 times the recommended amount in order to reach the equivalent dose. A dosage this severe is never advisable.
Summary Although some studies in rodents show that raspberry ketones can protect against weight gain and fatty liver disease, these studies used massive dosages — much higher than you would get with supplements.
There is not a single study on raspberry ketones in humans.
The only human study that comes close used a combination of substances, including caffeine, raspberry ketones, garlic, capsaicin, ginger and synephrine ().
In this eight-week study, people cut calories and exercised. Those who took the supplement lost 7.8% of their fat mass, while the placebo group lost only 2.8%.
However, the raspberry ketones may have had nothing to do with the observed weight loss. The caffeine or any of the other ingredients could be responsible.
Comprehensive studies in humans are needed before the effects of raspberry ketones on weight can be fully assessed.
Summary There is no evidence that raspberry ketone supplements can cause weight loss in humans. More research is needed.
One study links raspberry ketones to cosmetic benefits.
However, this study was small and had a number of flaws. More studies need to confirm these effects before any claims can be made (21).
Summary One small study proposes that raspberry ketones, administered topically, can increase hair growth and improve skin elasticity.
Because raspberry ketones haven't been studied in humans, potential side effects are unknown.
However, as a food additive, raspberry ketones are categorized as "Generally Recognized as Safe" (GRAS) by the FDA.
While there are anecdotal reports of jitteriness, rapid heartbeat and increased blood pressure, there are no studies to support this.
Due to the lack of human studies, there is no science-backed recommended dosage.
Manufacturers recommend dosages of 100–400 mg, 1–2 times per day.
Summary Without human studies on raspberry ketones, there is no good data on side effects or a science-backed recommended dosage.
Of all weight loss supplements, raspberry ketones may be the least promising.
While they seem to work in test animals fed extreme doses, this has no relevance to the doses commonly recommended in humans.
If you’re trying to lose weight, focus on other techniques instead, such as eating more protein and cutting carbs.
Lasting, beneficial changes in your lifestyle are much more likely to have an impact on your weight than raspberry ketones.