The Sweetest Thing Might Not Be Sugar, but a Beam of Light Shone Into the Brain
Ranked by sweetness potency, sugar is not the sweetest; but by the sweetness you actually taste, sugar is almost impossible to surpass. More radically, using lasers to directly light up sweet neurons could theoretically create a sweetness humans have never tasted.
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The number one on the sweetness ranking is not sugar
The food industry really does rank sweet molecules, with sucrose as the benchmark. Honey is about 1.5 times sucrose, aspartame about 200 times, the katemfe fruit from West African rainforests about 2000 times, advantame about 20000 times, and the top-ranked lugduname about 300000 times—a tiny pinch can sweeten an entire swimming pool. But Eric Walters says this ranking only measures potency, that is, ‘using the least amount of stuff to light up the sweet receptor’, which is useful for soda and chewing gum factories, but is a different thing from ‘how sweet it actually tastes’.
— Eric WaltersSomething 20000 times sweeter, a child spat it out
Latif gave his own child the second-ranked advantame, and the child immediately spat it on the ground and scraped his tongue with his fingers. Scientists say it is 20000 times sweeter than sugar, but it does not taste sweet. The reason is that there is only one type of sweet receptor, but twenty to thirty types of bitter receptors. Creating a molecule that triggers only sweet and touches no bitter receptor is like tiptoeing through a minefield. So many sugar substitutes carry off-flavors.
— Latif NasserThe sweet receptor is a dimmer, not a switch
Paul Breslin of Rutgers says that if you keep adding advantame to water, the sweetness does not keep rising to the moon, but reaches a plateau. The sweet receptor is not like a switch, but more like a dimmer, which can get brighter and brighter, but sugar substitutes can only brighten to a certain point. By the standard of ‘how far you can turn the dimmer up’, Eric Walters says sugar might be the sweetest—he has never tasted anything sweeter than sugar. The episode goes around in a big circle and returns to the starting point, but for a deep reason: glucose is the brain's best fuel, and the sweet receptor evolved for sugar in the first place.
— Paul BreslinStrawberries taste sweeter than blueberries, but blueberries have more sugar
Blueberries actually contain twice the sugar of strawberries, yet strawberries taste sweeter. The mechanism is volatiles: strawberries release non-sugar odor molecules that are pumped from the back of the mouth into the nasal cavity when you chew and swallow. These olfactory signals and taste signals overlap in the brain, giving sweetness a boost. Vision works the same way: dye the same sugar red, or shape it to look like fruit, and perceived sweetness rises. Latif did a live experiment with honey plus strawberry flavoring and red coloring, and after tasting it Lulu said ‘noticeably sweeter’.
— Linda BartoszikHigh-pitched tones can boost sweetness by another ten percent
In research at the London Science Museum, certain high-frequency tones can increase perceived sweetness by 5% to 10%. Latif played them for Lulu, and she said ‘more layered, more sparkling, more crystalline’, but she also admitted this step was much subtler than the strawberry step, and that honey itself crystallizes over time, which could be a confound. Why sound affects sweetness, the episode explicitly says no one knows the exact reason, it just repeatedly shows up in experiments.
— Latif NasserPutting bitter receptors onto the sweet pathway
Charles Zuker at Columbia University traced the entire sweet signal path from tongue to brain: tongue to ganglion, to brainstem, to another station in the brainstem, then to thalamus, and finally to cortex—only when it reaches cortex do you say ‘this is sweet’. His experimental method is direct: normally cells carry sweet receptors, so sweetness activates this pathway; if you swap in bitter receptors there, bitter chemicals will activate the same sweet pathway. He does this not to find the sweetest thing, but to understand how sweetness and taste work in the brain, which might help with addiction, obesity, eating disorders, and diabetes.
— Charles ZukerUsing lasers to make mice taste a sweetness that isn't there
Zuker's team implanted a light switch only in the sweet-sensing neurons of mice, and inserted an optical fiber into their heads. Turning on the laser triggers these neurons, and the brain says ‘sweet’—even though the mouse is eating nothing. Latif pressed: could you turn the laser to maximum and create a sweetness humans have never tasted? Zuker said in principle it's imaginable, you could possibly create the sweetest sweet, and the sweetest thing could be light. Lulu's reaction was resistance: this would completely strip pleasure from the real world, to the point where you wouldn't even need to go outside.
— Charles ZukerThe kind of sugar in raspberries drifts in interstellar dust
A research team at the Spanish Center for Astrobiology observed a cloud of interstellar dust and gas near the center of the Milky Way, read its composition with spectroscopy, and found a large amount of erythrulose—a four-carbon sugar. This is the first time humans have found sugar in deep space, and a relatively complex sugar at that. Coincidentally, erythrulose also happens to exist in raspberries. Latif joked that maybe somewhere there really is a space raspberry. This segment pushes ‘the sweetest thing’ from the tongue to the cosmic scale.
— Latif NasserIn their own words · checked verbatim
So the thing that scientists say is 20,000 times sweeter than sugar does not actually taste sweet?
Latif Nasser8:25
You'll eventually reach a point where the sweetness intensity sort of reaches a plateau. The amount of sweetness that you perceive sort of levels off.
Paul Breslin10:30
It's not just like a regular light switch you turn on or off. It's more like a dimmer switch.
Paul Breslin11:34
The sweet taste of mother's milk. The sugar in the mother's milk. Is what keeps it nursing.
Linda Bartoszik12:36
in principle, I could imagine, yes, you could potentially create the sweetest sweet.
Charles Zuker23:51
The sweetest thing could be light.
Latif Nasser24:51
This is the first time ever they found a not only a sugar, a relatively complex sugar in deep space.
Latif Nasser26:55
Figures
| Sweetness of honey relative to sucrose | about 1.5 times | 4:05 |
| Sweetness of aspartame relative to sucrose | about 200 times | 5:11 |
| Sweetness of katemfe fruit relative to sucrose | about 2000 times | 5:11 |
| Sweetness of advantame relative to sucrose | about 20000 times | 6:16 |
| Sweetness of lugduname relative to sucrose | about 300000 times | 6:16 |
| Sweetness of the sweetener Eric Walters himself discovered | about 28000 times sucrose | 7:18 |
| Number of human bitter receptors | about 20 to 30 types | 9:29 |
| Increase in perceived sweetness from high-frequency tones | 5% to 10% | 18:43 |
| Sugar content of blueberries relative to strawberries | twice | 14:39 |
| Sugar found in deep space | erythrulose, a four-carbon sugar | 26:55 |
Glossary
- potency
- The ability to light up the sweet receptor with the least amount of substance; the metric used in food industry rankings.
- volatiles
- Small molecules floating in the air that produce smell and can enter the nasal cavity from the back of the mouth to affect taste.
- optogenetics
- Implanting light-sensitive proteins into specific neurons to turn neuronal activity on and off with light.
- erythrulose
- A four-carbon sugar that exists in raspberries and has also been found in interstellar dust.
How to listen
Listeners interested in taste, the food industry, neuroscience, and brain-computer interfaces; product managers working on sugar substitutes, flavor enhancement, or sensory marketing can also get concrete mechanisms.
The opening 0:00-1:01 is a membership donation pitch and can be skipped directly.