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It’s that time again. The new year has begun and, as every year, many resolve not to wait until spring to get in shape. So, it was no surprise when last week a friend asked me what I thought about Raspberry Ketones, a product that is increasingly being hyped as the fat burner.
What are Raspberry Ketones?
Raspberry Ketones, chemical name
4-(4′-hydroxyphenyl)butan-2-one, are the component of raspberries that give them their smell. Besides raspberries, they are also found in cranberries and blackberries (1). Raspberry Ketones are often used in the cosmetic and food industry as a fragrance. However, Raspberry Ketones occur only in small amounts in nature. For example, a kilo of raspberries yields only 1-4 mg of Raspberry Ketones (2). Therefore, the synthetic form, which is much cheaper than the natural form that costs almost €15,000 per kilo (2,3), is used in the industry and thus also in slimming products.
Dr. Oz on Raspberry Ketones: “The number 1 miracle in a bottle”
“The wonderful world of Dr. Oz”. That’s what I thought when I heard him on his program talking about Raspberry Ketones. Dr. Oz calls Raspberry Ketones: “The number 1 miracle in a bottle”. He and his guest talk about “research” that gave them insight into the effectiveness of Raspberry Ketones, but then do not mention the research itself. However, he does a fun trick with balloons that he puts in liquid nitrogen, causing them to shrink. This is supposed to be the same effect that Raspberry Ketones have on fat cells. His guest, according to Dr. Oz a “weight loss expert”, recommends using 100mg to 200mg per day. The first effects would be visible after just a few days, where we get to see the usual before and after photos of women who have been using Raspberry Ketones for six and eight months. “Once you go
black, (sorry, I mean) Raspberry Ketones, you’ll never get off it” or something along those lines, she says.
People who use it would never want to stop. The broadcasts of Dr. Oz about Raspberry Ketones caused a real run on the product in the US, leading to empty shelves. Strangely enough, the “scientific proof” for this is not at all convincing. Moreover, the experiences I read online are not so positive. “Luckily there’s such a thing as a money-back guarantee,” shouts a wise guy now. Unfortunately, that’s exactly what some of the complaints are about. But let’s first look at how Raspberry Ketones are supposed to work and then see how much of this is actually true in practice.
Raspberry Ketones for more fat burning
Dr. Oz explains that Raspberry Ketones affect the hormone balance and more specifically the hormone adiponectin. Adiponectin is a (protein) hormone involved in regulating blood sugar levels and the breakdown of fatty acids (4). Research shows that there is a negative relationship between the amount of adiponectin in the blood and body fat (thus, more adiponectin means less body fat) (5,6,7,8). For example, research in mice has shown that metabolism is increased when there is more adiponectin in the blood (9). Moreover, a higher level of adiponectin lowers the chance of type II diabetes (5,10). Adiponectin also increases with moderate consumption of alcohol (10,11), except in Asian people where there is a (small) negative relationship between adiponectin and alcohol consumption (12). However, the references on Dr. Oz’s site do not include any research showing that adiponectin levels increase by taking Raspberry Ketones.
The “scientific proof” that Raspberry Ketones help burn fat
Granted, Dr. Oz and his guest show the tip of the iceberg, but they don’t let the cat out of the bag. At the end of the story, the “weight loss expert” says that her clients, like the ladies in the before-and-after photos, were first taught to eat healthily and exercise enough. Without knowing the effect of diet and exercise on the one hand and the effect of Raspberry Ketones on the other, you cannot assume that Raspberry Ketones contributed to the weight loss. This could have been caused by the exercise and diet alone. This is precisely where the studies also go wrong. On the site with the video, there is a link at the bottom to “the scientific evidence”. Here, several statements are made with references on the third page that are supposed to substantiate these statements. Good, that’s how it should be. Then you can read the studies yourself to see if you would come to the same conclusion.
Irrelevant references
The first two studies mentioned (13,14) are only about how the synthetic form is made and will therefore not be further discussed.
More references for capsaicin than for Raspberry Ketones. Are they really comparable?
Then, no fewer than four studies are cited that deal with the effect of capsaicin on metabolism (15,16,17,18). These references are only mentioned because (the team behind) Dr. Oz claims that the effect of Raspberry Ketones is comparable to that of capsaicin. Both would increase the amount of
norepinephrine/noradrenaline, leading to an increase in body temperature and thereby increased thermogenesis, the heat generated by burning calories.
That both, apart from their structure, are actually comparable in action, would be supported by a study in rats (19). However, no control group was used for this study. It is at least odd to show four studies (almost half of all given references) about capsaicin and then only one study that should show that Raspberry Ketones are comparable to it. So far, we have seen two studies explaining how Raspberry Ketones are made, four studies about a completely different product, and one study in rats without a control group. Dr. Oz better hope that something better is among the references he provided, but unfortunately, this is not the case. Another study not given as a reference but which I believe is referred to in the TV program concerns the influence of Raspberry Ketones on fat cells of mice. So, it looked at the effect on isolated cells, outside the body. The body, however, is complex with countless things influencing each other (20). It is therefore not certain that this effect would be the same in the body.
Mice are not humans. Research useful, but not always translatable to humans.
The main point, however, is that although animal studies can be very useful, the conclusions can never be directly translated to humans.
There is, in fact, not a single study conducted on humans on the effects of Raspberry Ketones on fat burning! Although this is nowhere mentioned in the TV program itself, fortunately, it is mentioned in the text about the “scientific evidence”. Here, it is noted that animal studies are not always translatable to humans and research on humans still needs to be done. The best reference they give in the list is, in my opinion, the reference to the study showing that conclusions from animal studies do not necessarily apply to humans for various reasons (21).
Side effects of Raspberry Ketones
This is also important when it comes to potential side effects. Although Raspberry Ketones were approved by the American FDA as a supplement in the sixties, nothing is known about any side effects. Dr. Oz’s guest also proudly says: “With no known side effects!”. However, the fact that they are not known does not mean they do not exist. Simply no research has been done, so no one knows about the long-term effects. If Raspberry Ketones work as claimed and are indeed comparable to, for example, capsaicin, then it poses risks to certain groups. Increasing body temperature, blood pressure, and heart rate could be a problem. For example, there is a known case of someone who had a heart attack after taking capsaicin (22).
It is therefore advisable to consult a doctor first if you have certain conditions.
Conclusion, would I buy Raspberry Ketones?
Although the animal studies may not be translatable to humans and also not entirely correctly conducted, the conclusions from them are quite encouraging. In this respect, I find it plausible that there is a chance that Raspberry Ketones can help with fat burning in addition to exercise and a healthy diet. However, to shout from the rooftops in terms like “miracle in a bottle” and “proven by research” seems unwarranted to me. Much more and better research needs to be done, and it needs to be done on humans. Looking at the experiences mentioned on the internet, we would probably be (even) less positive.
