It would have been easy to dismiss the claim out of hand by playing armchair skeptic, but I decided instead to stuff the lawn clippings in my mouth. It really did look like someone had been chasing after lawn mowers to resell the leftovers for a profit, and though I have never tasted grass clippings, I can imagine what I was sampling wasn’t a million miles away.
Once the leaf powder had coated my tongue long enough and I had swallowed it up, I picked up the candy from my desk. When it hit my tongue, I could still smell its artificial raspberry flavour but the sweetness was gone. I was chewing on cardboard.
Many of us in the Office tried this “miraculous” powder (dissolved in a smoothie or tea instead of straight up, as I had foolishly done), and there was no mistaking its effect. This ground-up leaf really did cancel out our perception of sweetness for 30 to 60 minutes. Any craving we had for dessert was quickly curbed. No more cardboard, please.
Could this be the long-awaited messiah to deliver us from diabetes and obesity?
Tremble before the Destroyer of Sugar
The plant is named Gymnema sylvestre. It is a woody climber found in India, parts of East Asia, Africa, and even Australia. In traditional Indian medicine (Ayurveda), Gymnema is a cure-all: it can apparently treat rheumatism, ulcers, asthma, and even snake bites. If it sounds too good to be true, it’s because it probably is, although it is important to state that plants do create a large number of chemicals that help them interact with (and protect themselves from) their environment. These molecules can protect the plant from predators, attract pollinating insects, or even serve as nature’s text messages by signalling other plants. Over 60% of cancer drugs approved since 1940 are derived from natural products, including chemicals from plants, so it is entirely plausible that Gymnema contains compounds that could be used or adapted to help treat conditions in humans.
One of the Hindi names for Gymnema is gurmar, which means “destroyer of sugar”. Indeed, the plant is able to temporarily mask our ability to taste sweetness. It used to be thought that it was a molecule called gymnemic acid that was responsible for this cool little parlour trick, but it turns out that “gymnemic acid” was actually a mixture of many molecules. These gymnemic acids can bind to the sweetness receptors on our tongue, which means that sugar and artificial sweeteners no longer can. It’s like blocking all the USB ports on your computer with inert dongles. Your computer can no longer detect your external hard drive because it can’t connect to it.
The effect is well known (so much so that even Coca-Cola used it in a study to counteract Miracle Fruit, which itself turns acidity into sweetness), but it seems to vary from person to person. When we did our little experiment, someone got the same dose but did not immediately respond to it. It took a doubling of the dose before they noticed that sweetness had been drastically reduced. Gymnemic acid lozenges also did not work for the journalist who tried them for The Cut, and many reviewers on Amazon likewise have reported not tasting the difference.
But since it works for many, Gymnema is being presented as a great way to lose weight. When you’re done with your main course, you allow a lozenge of Gymnema to dissolve on your mouth, and when you reach for that ice cream sundae, you quickly put it aside because it tastes like fatty chalk. Fewer calories in your system. And also, if you have diabetes, less sugar in your blood.
There is however a big difference between plausibility and a demonstrated benefit.
Small trials and conflicts of interest
The studies I could find on Gymnema to curb sugar intake all suffered from a number of important problems, a reminder that while science is a fantastic set of tools for gaining knowledge about the world, there is a large gap between our ideals of rigour and the reality of scientific experimentation.
The first problem is small sample size. The studies involve between 27 and 44 participants per group, which makes any result questionable.
The second issue is the potential cultural bias. The first two studies of Gymnema were conducted in India in 1990. Given Gymnema’s almost mythic status in the country’s folkloric medicine, appropriate skepticism is warranted toward these early positive results. Indeed, it is a well-known fact in skeptical circles that 99.8% of all acupuncture trials coming out of China show that acupuncture works. It seems that finding out acupuncture does not work (as many non-Chinese studies have provided evidence for) “would be very offensive for Chinese researchers.” Likewise, studies of an Ayurvedic remedy like Gymnema conducted in a country that embraces Ayurveda may not be completely reliable.
The third major problem of these studies is the financial conflict of interest. A randomized clinical trial published in 2003 and which used Gymnema as part of a dietary supplement was funded and conducted by the company that made the supplement. Ditto for the Crave Crush studies (a product later renamed Sweet Defeat), where the company was behind both trials. In fact, the paper reporting on the first trial admits that the company requested the researchers stop recruitment early because they were happy with the current results, which already showed a bigger effect than hoped for. This reminded me of p-hacking (essentially hacking your way to a significant result by throwing rigour out the window). Many would agree this renders an otherwise methodologically interesting (though small) study open to doubt.
Hungry for better data
When the evidence for Gymnema was reviewed in 2015 by the website Practice-Based Evidence in Nutrition (developed by Dietitians of Canada and co-managed with the Dietitians Association of Australia and the British Dietetic Association), the supplement was listed as “supported by limited evidence or expert opinion” for glucose control in adults with diabetes.
It may sound obvious that a supplement that makes sweets taste like cardboard would lead to weight loss and to better outcomes for patients with diabetes, but plausibility is not enough. Here’s a recent example. If low vitamin D levels are a risk factor for diabetes, taking vitamin D supplements should reduce our risk of developing diabetes, right? A recent major study showed that it did not overall. In her commentary on this clinical trial, Dr. Harriet Hall of Science-Based Medicine reminded us that “common sense can be wrong”: we need to test our hypotheses.
We could probably use more rigorous studies of Gymnena, away from financial conflicts of interest and the cultural belief in its panacean potency. If you do feel like trying it, a word of advice (or two). The powder on its own is unpalatable and begs to be mixed in with something else. Also, while there are very few reported side effects (though no rigorous long-term toxicological studies), it remains a natural product. As a Canadian study showed in 2013, contaminants, fillers, and outright substitution are not rare when it comes to these poorly regulated products.
Gymnema may have temporarily dampened my craving for sugar, but it did not suppress my appetite for more rigorous scientific studies.
Take-home message:
- Gymnema sylvestre is a plant that contains molecules that cancel out the taste of sweetness in our mouth for 30 to 60 minutes
- It has been said to be helpful to lose weight or manage diabetes, but the few scientific studies done so far have been too small and often funded by the companies who want to sell a product containing Gymnema
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