They are supposedly a "magical" fat burner, and Dr. Oz is apparently pretty high on them. Also, stores can't keep these bad boys in stock! But is there really any science to back this holy grail of fat burning up?
No.
If you pubmed "Raspberry Ketones" you get these 2 WHOLE PAGES of results. Wow! What a lot of research has been done on these! And when you go through these two pages of results, you see that most of the articles are about extraction of these guys from various fruits, or how to synthesize them.
If we refine our search and type in "Raspberry Ketone Lipolysis", becasue Dr. Oz tells us they trigger lipolysis, we get three entire papers!
Wow three articles, even more research to back up Dr. Oz! Let's look at each one in turn.
The First one (1). Unfortunately, I was unable to get the full text for this guy, even when I went to the library on campus, so we will have to see what we glean out of the abstract. Lets break this one down and see what they were actually studying. First, they were using an isolated cell line, 3T3-L1. These cells are a fibroblast like cell, that can develop an adipose cell-like morphology under the right conditions (2). Also, they are more sensitive to lipogenic and lipolytic hormones and drugs. To these isolated cells they added 10 µM of Raspberry Ketones. This treatment significantly increased lipolysis, and expression/secretion of adiponectin, a hormone made in fat tissue. It is unfortunate here that I don't have the full text, as I wonder what was in the media the cells were grown in. However, as we all know, a human body is a complicated system that works in a systemic way, so it is tough to take our isolated cell culture results and extrapolate them all the way to humans.
On to the next one!
This second one is probably one of the more interesting ones to be used to prove that raspberry ketones have a lipolytic effect in humans (3). In this study no animal cells were used at all, they simply dumped some chemicals together in a vial and looked at how much fat was broken down. Here's what they did: They took a small amount of olive oil and added a variety of chemical extracts they found in various citrus fruits, mixed them together for a while, and then looked at how much of the olive oil had been broken down into its main constituent fatty acid, oleic acid. When they did this they actually found that several chemicals were BETTER than raspberry ketones and breaking down olive oil. Here is the table.
(3)
The smaller the bar, the more fat was broken down, as it is reported as ratio of fat remaining. Not only are several extracts better than raspberry ketones at breaking down fat, but it looks like you need very high concentrations, 5 mM, to get a significant amount from raspberry ketones themselves. Remember that from the last article the authors only used 10 µM, so going up to 5 mM represents at least a 1000x increase. Also, if you are going to use this to support the hypothesis that raspberry ketones aid in weight loss, why aren't you trying to sell octanal as a weight loss supplement as well? It is the most lipolytic of all the compounds tested!
In the end I don't think this study tells us anything about the ability of these compounds as a weight loss supplement in humans. Do you know what else would exhibit these same effects if you incubated it in a vial with some fat? Detergents. I don't see many people lining up to take detergent to lose weight!
And finally, we come to the only study that was done in an actual animal model (4). This study gave mice 1% of total energy in the form of raspberry ketones with a high-fat diet known to promote obesity in their mouse strain, or just the high-fat diet itself. When they did this (after fattening the mice up for 6 weeks) both the high-fat diet group and the raspberry ketone group lost a bit of weight over the first week, but then started to gain it back. At the end the 5 week period the raspberry ketone group had gained back less weight than the high-fat diet group. They don't ever mention what caused the weight loss in the first week, if they had them eating less or something, so it is not possible to say the raspberry ketones were the cause of the weight loss.
Next they took out some of the fat cells and incubated them with varying concentrations of raspberry ketones, much like the other two studies. Again, they found that raspberry ketone concentrations approaching 1 mM significantly increased lipolysis. This is a much higher concentration than you will ever see inside an actual, living animal, so it is tough generalize this result all the way to humans. So, I think the conclusion that most closely resembles what Dr. Oz says is that a diet containing 1% raspberry ketones will decrease the obesity promoting effect of an obesogenic diet.
Well there you go! Those are all THREE of the studies that looked at the lipolytic effects of raspberry ketones in various model systems. I think we can see that there is essentially no evidence that raspberry ketones promote lipolysis in a human, and the only times we see lipolysis is at concentrations you would never get inside an living animal. There was only one study done in an actual animal, and they only showed a decrease in fat accumulation over time when raspberry ketones were incorporated into the diet. With this data I find it hard to believe Dr. Oz's claims that this is a magic fat loss supplement. The effects of raspberry ketones seem to be in line with things like capsaicin, the compound that gives peppers their spice, and is known to be beneficial for weight management. However, even with this few people take capsaicin extract, there are just better and more economical ways to lose weight that these gimmick supplements.
On a side note, some of you may have been wondering about the "ketone" part of raspberry ketones, especially as I have written extensively about the benefits of ketones and ketosis. However, as I mentioned in the very first article, a "ketone" is just an organic functional group, and the only physiologic ketones humans use for energy are beta-hydroxybutyrate, acetoacetate, and acetone. So, while this is a ketone in the literal sense of the word, it is not at all related to ketosis or the ketones we use as fuel.
P.S. For those of you who recognize the quote that makes up the title, congratulations! For those who don't educate yourselves (skip to 2:15 is just want to hear the quote, but the whole video is pretty good!)
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