Everybody loves the smell of raspberries: fruit flies, perfume makers and, as Katrina Krämer explains, overweight rodents.
Losing weight is hard work. cookbooks and diet plans try to lure the reluctant dieter into a false sense of effortless slimming, featuring images of fresh, healthy, colourful food. Raspberries look like the perfect health food: pink, bright and tasty. Maybe this is the reason the slimming industry has adopted raspberry ketone, the substance that gives the raspberries their enticing aroma and flavour, as their latest weight-loss ‘miracle’.
Among the compounds that make raspberry so delicious, raspberry ketone is one of the most recognisable. Only one to four micrograms gives each raspberry their intense smell and taste. Although most abundant in their namesake berries, blackberries and cranberries also hold small amounts of this simple phenolic ketone.
Not only do the food and perfume industries love the ketone’s smell – fruit flies do too. In a bid to attract the little insects and get them to pollinate their flowers, some orchids even produce nectar rich in raspberry ketone. But back to the slimming miracle pills. Weight loss is big business and obesity is an ever-growing problem in many countries. Not only could a weight-loss drug save many lives, but there are also many people who would spend a pretty penny on an easy way to lose those few extra pesky pounds. There are already a few obesity drugs on the market, but they come with an array of side effects: from unpleasant but ultimately harmless things, like stomach pain, to severe long-term effects such as heart valve problems and high blood pressure.
Until scientists develop a slimming pill that doesn’t have major side effects, the food supplements industry supports itself with (in their own words) ‘talked-about potential breakthroughs’. Little pink pills, each containing around 200 to 500 milligrams of raspberry ketone, are one of those potential breakthroughs. I wonder how well these pills would sell if they were marketed as what they actually are: slimming pills for obese rodents.
In 2005, Japanese researchers became interested in raspberry ketone because it’s a natural products with a similar chemical structure to capsaicin, the spicy chemical in chillies, and also to synephrine, a substance found in oranges. Both of these compounds alter lipid metabolism and decrease adipose tissue in overweight lab animals. They found that the same was true for raspberry ketone: having first fed some mice on a tasty diet of lard for a few weeks, the team then supplemented the now overweight rodents’ food with raspberry ketone. Adding 1% of raspberry ketone – an arguably large amount – to the mice’s diet slowed the animals’ weight gain even though they were still eating their daily portion of fatty food. It even prevented fatty liver disease – a common problem that accompanies obesity and causes abnormal liver function and all its associated problems.
These results seemed encouraging. Other researchers went on to confirm raspberry ketone’s slimming effect on overweight rats. But is it practical in people? How many raspberries would a human need to eat to get their daily intake of 1 per cent weight raspberry ketone? Though daily food amounts vary depending on country, on average a person eats around 2kg of food per day. This means a person would need to consume 20g of ketone to match the obese rodents’ diet. That doesn’t sound like much, but consider that one kilogram of raspberries only contains between one and four miligrams of ketone. Even in the best case scenario – raspberries packed with 4mg ketone per kg – it would mean having to eat 5000kg, or five metric tonnes of berries every day… not exactly what I would call a balanced diet. Even commercial capsules contain only around 200–500mg of raspberry ketone. A person would still need 40 of the highest dose pills to match the proportions used in the mouse research.
So research hasn’t yet confirmed that any amount of raspberry ketone has an effect, slimming or otherwise, in humans. And consuming large volumes of ketone-based supplements may not be wise - although we know very little about the health effects of raspberry ketones themselves, the diet pills they’re sold as often contain large amounts of caffeine, which can be fatal. In 2013, after a devastating break-up, a British woman took a large amount of raspberry ketone diet pills after which she went into seizure and fell unconscious. Despite being rushed to the hospital, she died of a cardiovascular collapse. Each slimming capsule contained about 60mg of caffeine, about as much as one espresso. The number of pills she took amounted to an ultimately lethal dose of caffeine.
Although further research may create a raspberry-flavoured diet aid, it turns out that a miracle pill for fat loss doesn’t exist; at least not yet. But perhaps you can feel a little more virtuous when tucking into fresh raspberries.
Katrina Kramer on raspberry ketone. Next week, we go from a sweet smelling fruit to a poisonous root
The compound itself is contorted tangle of fused and bridge rings attached to an aromatic molecule, looking somewhat like a failed attempt to make a 3D molecule of a cow out of drinking straws. Its chemical formula C34H47NO11 does not give a realistic feel for that tortured structure. With an ability to cross the blood-brain barrier, the poison interferes with the crucial sodium-ion signalling channels, rapidly taking effect after consumption. Its impact is felt in minutes and the poison can cause cardiac arrest or respiratory failure within an hour.
Join Brian Clegg next week to discover the poison at hand, and why the plant it comes from is said to ward off werewolves. Until then, let us know if there’s anything you’d like to hear more about by emailing email@example.com, or tweeting @chemistryworld. I’m Ben Valsler, thanks for listening.
If you need to lose weight, you are not alone.
More than a third of Americans are overweight, and another third are obese (1).
Only 30% of people are now at a healthy weight... being overweight has become the new "normal."
The problem is, conventional weight loss methods are so difficult that 85% of people fail in the long run (2).
However... there are many products out there that are claimed to make things easier.
These are herbs, shakes and pills that are supposed to help you burn fat or reduce your appetite.
Among the most popular ones is a supplement called Raspberry ketones.
Raspberry ketones are claimed to cause the fat within cells to be broken down more effectively, helping the body burn fat faster. They are also claimed to increase levels of adiponectin, a hormone that helps to regulate metabolism.
This article reviews the current scientific research behind raspberry ketone supplements and whether they are actually worth considering.
What are Raspberry Ketones?
Raspberry ketone is a natural substance that gives red raspberries their powerful aroma.
This substance is also found in small amounts in 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 flavorant.
Actually... most people are already eating small amounts of raspberry ketones, either from the fruits themselves or because of their popularity as a flavorant (3).
Only recently did they became popular as a weight loss supplement.
Even though the word "raspberry" may appeal to people, the supplement is actually NOT derived from raspberries.
Extracting raspberry ketones from raspberries is insanely expensive, because you need 90 pounds (41 kg) of raspberries to get the amount needed for a single dose!
In fact, a kilogram (2.2 pounds) of whole raspberries only contains 1-4 mg of raspberry ketones. That's 0.0001-0.0004% of the total weight.
The raspberry ketones you find in supplements are synthetically made via an industrial process and are not natural (4, 5, 6).
Another reason for the appeal of this product is the word "ketone" - which associates it with low-carbohydrate diets, which force the 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.
Bottom Line: 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.
How Do Raspberry Ketones Work?
Researchers became interested in raspberry ketones because of the molecular structure.
They noticed that it looked very similar to two other molecules, capsaicin (found in chili pepper) and synephrine (a stimulant).
Several studies have shown that these two molecules can boost metabolism (7, 8), so it was speculated that raspberry ketones could have the same effect.
When researchers took isolated fat cells from rats and made them grow in a test tube, adding raspberry ketones to the mix had two effects (9):
- It increased lipolysis (breakdown of fat), primarily by making the cells more sensitive to the effects of the fat burning hormone norepinephrine.
- It made the fat cells release more of the hormone adiponectin.
Adiponectin is a hormone that is released by fat cells and is believed to play a role in regulating metabolism and blood sugar levels.
Thin people have much higher levels of adiponectin than people who are overweight and the levels of the hormone increase when people lose weight (10, 11).
Studies have shown that people with low adiponectin levels are at a higher risk of obesity, type 2 diabetes, fatty liver and even heart disease (12, 13).
Therefore, it stands to reason that raising adiponectin levels with natural means could help people lose weight and lower the risk of many diseases.
However... even if raspberry ketones raise adiponectin in isolated fat cells from rats, this does NOT mean that the same will happen in a living, breathing organism.
Also keep in mind that there are natural ways to increase adiponectin. For example, exercise can increase adiponectin levels by 260% in as little as one week. Drinking coffee is also linked to higher levels (14, 15, 16).
Bottom Line: Raspberry ketones have a similar molecular structure as two known fat burning compounds. They can make isolated fat cells break down fat and release a hormone called adiponectin.
Some Studies Show That it Works in Rats, But The Dosages Were Insanely High
Raspberry ketone supplements have shown some promise in studies on mice and rats.
However, the results weren't nearly as impressive as the supplement makers would have you believe.
In one of the studies, a bunch of mice were fed an unhealthy, fattening diet. Some of the mice got raspberry ketones... others did not (17).
This is what happened:
The mice in the raspberry ketone group weighed 50 grams at the end of the study. The mice that didn't get raspberry ketones weighed 55 grams (a 10% difference).
Keep in mind that the rats in that study did NOT lose weight, they just gained less than expected.
Another study was conducted in 40 rats, also fed a fattening diet. In this study, the rats given raspberry ketones had increased adiponectin levels and were protected against fatty liver (18).
However... I don't think you should get your hopes up though, because these were massive dosages.
You would have to take a 100 times the recommended amount in order to reach the same dose as the test animals (NOT recommended).
Bottom Line: Some studies in mice and rats show that raspberry ketones can protect against weight gain and fatty liver. However, these studies used massive dosages, much higher than you would get with supplementation.
Do Raspberry Ketones Work in Humans?
Unfortunately, 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 (19).
In this 8 week study, the participants lost 7.8% of their fat mass, compared with the placebo group which lost only 2.8% (both groups also cut calories and exercised).
However, it is highly possible that the raspberry ketones had nothing to do with it. It could have been the caffeine or any of the other herbs.
Really... I looked long and hard and I am 100% certain that there isn't ANY actual evidence showing that this supplement can work in humans.
From looking on forums and reviews online, the pattern seems similar to other weight loss supplements. Some people lose weight, others don't, and some people even gain weight while taking the supplement.
It's important to keep in mind that just because someone on TV or someone you know lost weight with raspberry ketones, it does NOT mean that the supplement had anything to do with it.
Even when people lose, chances are that it is just a placebo effect.
Many studies show that placebo (a dummy pill) can have an effect on people.
Maybe they want the pills to work, so they start weighing themselves more often, eating more mindfully, feeling more motivated to exercise, etc.
Therefore, it could just be these behaviors that caused the people to lose weight, not the supplement itself.
Of course, it is still possible that raspberry ketones DO work, that it just hasn't been proven yet... but given how incredibly large the dosages need to be to see an effect, then I personally think this is unlikely.
Bottom Line: There is currently no evidence that raspberry ketone supplements can cause weight loss in humans.
Do Raspberry Ketones Have Any Other Benefits?
One study has shown that raspberry ketones can have cosmetic benefits.
When administered topically, as part of a cream, it has been shown to increase hair growth in people with hair loss, as well as improve skin elasticity in healthy women (20).
However, this study was small and had a number of flaws, so it should not be used as evidence of anything (21).
Bottom Line: One small study shows that raspberry ketones, when administered topically, can increase hair growth and improve skin elasticity.
Side Effects and Dosage
Because they haven't been studied in humans, there is no data about potential side effects.
However, as a food additive, raspberry ketones are categorized as "Generally Recognized as Safe" (GRAS) by the FDA.
Keep in mind that the FDA also puts high fructose corn syrup and soybean oil in the same category, so take that with a big grain of salt.
Looking online, there have been some anecdotal reports of jitteriness, rapid heartbeat and increased blood pressure, but this could have been a coincidence.
The mouse and rat studies used massive dosages and no harmful effects were noted, so it seems to be safe in test animals.
Due to the lack of human studies, there is no science-backed recommended dosage.
The recommendations on different raspberry ketone supplements range from 100 mg to 400 mg, 1 to 2 times per day.
Bottom Line: Because there are no human studies, there is no good data on side effects or a science-backed recommended dosage.
Should You Try Raspberry Ketones?
Of all the weight loss supplements I have reviewed (including Yacon Syrup and the disappointing Garcinia Cambogia), raspberry ketones are the least promising.
They seem to work in isolated fat cells and in test animals fed extreme doses, but this has absolutely no relevance to the doses commonly recommended in humans.
Given the fact that we would need such ridiculous doses to achieve the fat burning effects seen in the animal studies, I highly doubt that raspberry ketones will have any significant effect.
Just for the sake of self-experimentation, I even tried raspberry ketones for a few days. The only effect I noticed was a fruity burp.
If smelly, uncontrollable burps are a huge problem in your life, then perhaps raspberry ketones are something you want to consider.
But if weight loss is your goal... then you'd probably lose more weight from the calories burned walking to the store and buying the pills, than the pills themselves.
You are much better off spending your time and energy reading up on other weight loss methods that are actually proven to work, such as eating more protein and cutting carbs.
Raspberry ketones are not only a waste of time and money... they also distract you from doing the things that actually matter, which is making lasting, beneficial changes in your lifestyle.
One day we might find a supplement that actually works for long-term weight loss... but this is absolutely not the case with raspberry ketones. Period.