The Right Bacteria Can Turn Off a Sweet Tooth


We have a lot of control of our day to day lives; we get to choose where we go, who we see, and what we eat. But those decisions are often shaped by unseen forces, including some right under our noses (and all over our bodies for that matter). Scientists working with E. coli bacteria in mice say a taste for sweets might literally come from our guts. They present their findings this week in Florida at the annual meeting of the Association for Chemoreception Sciences. 

Some of the bacteria on our bodies are a force for good: they help us digest our food and stay healthy. Some are less helpful. Science is really just beginning to discover the many ways we interact with our bacteria. Some of our choices, like smoking, eating a low-fiber diet, or using deodorant, affect our bacteria. But the reverse may also be true: our bacteria could affect our choices.

This all has to do with the fact that these tiny organisms get hungry. Those in your digestive tract have it pretty easy: They just chow down on the food you shove in there. Some prefer fats, while others thrive on sugar. And if there are enough of them, what they want may become what you want.

“In our field, we are starting to think about how hormones and different factors affect the taste system, even at the level of taste buds, and contribute to obesity,” presenter Lynnette McCluskey said in a press statement. McCluskey is a neuroscientist at Augusta University's Medical College of Georgia. "Identifying the taste, whether it's sweet or not, is the first step in feeding. We wanted to know if you change the environment in the gut, what happens to the taste system."

McCluskey and her colleagues had previously found that they could reduce a mouse’s ability to identify sweet tastes by dropping a molecule called lipopolysaccharide (LPS) on its tongue. The LPS was extracted from the cell wall of E. coli bacteria, then detoxified so the mice would not get sick. 

For this experiment, the researchers wanted to find out if actually ingesting LPS could actually make mice lose interest in sweet flavors. They implanted small doses of detoxified LPS in each mouse’s gut, then offered them access to four sweeteners: glucose, sucrose (table sugar), saccharin (a.k.a. Sweet’n Low), and acesulfame potassium (a.k.a. Sweet One).  

Within 15 hours, mice dosed with LPS had higher levels of a hormone called leptin, which tells us when to stop eating. One week later, those mice had lost their preference for sweets. Even the number of sweet taste receptors on their tongues had decreased. It wasn’t that they’d lost their appetites altogether; the mice were still healthy and ate other food as they had before. It was just that sugar had lost its appeal. Yet seven days later, the rodents’ taste for sweetness had returned. 

The researchers were left with a number of questions. How did LPS in the gut cause a mouse’s body to make more leptin? Why did it take seven days to kick in? Why did it stop? And why leptin? "There may be other gut hormones involved as well,” said McCluskey, “but we know that leptin works.”

Big Questions
Why Do Onions Make You Cry?

The onion has been traced back as far as the Bronze Age and was worshipped by the Ancient Egyptians (and eaten by the Israelites during their bondage in Egypt). Onions were rubbed over the muscles of Roman gladiators, used to pay rent in the Middle Ages, and eventually brought to the Americas, where today we fry, caramelize, pickle, grill, and generally enjoy them.

Many of us burst into tears when we cut into one, too. It's the price we pay for onion-y goodness. Here's a play-by-play breakdown of how we go from grabbing a knife to crying like a baby:

1. When you cut into an onion, its ruptured cells release all sorts of goodies, like allinase enzymes and amino acid sulfoxides. The former breaks the latter down into sulfenic acids.

2. The sulfenic acids, unstable bunch that they are, spontaneously rearrange into thiosulfinates, which produce a pungent odor and at one time got the blame for our tears. The acids are also converted by the LF-synthase enzyme into a gas called syn-propanethial-S-oxide, also known as the lachrymatory factor (or the crying factor).

3. Syn-propanethial-S-oxide moves through the air and reaches our eyes. The first part of the eye it meets, the cornea, is populated by autonomic motor fibers that lead to the lachrymal glands. When syn-propanethial-S-oxide is detected, all the fibers in the cornea start firing and tell the lachrymal glands to wash the irritant away.

4. Our eyes automatically start blinking and producing tears, which flushes the irritant away. Of course, our reaction to burning eyes is often to rub them, which only makes things worse since our hands also have some syn-propanethial-S-oxide on them.

It only takes about 30 seconds to start crying after you make the first cut; that's the time needed for syn-propanethial-S-oxide formation to peak.


The onion's relatives, like green onions, shallots, leeks and garlic, also produce sulfenic acids when cut, but they generally have fewer (or no) LF-synthase enzymes and don't produce syn-propanethial-S-oxide.


Since I usually go through a good deal of onions while cooking at home, I've been road testing some of the different methods the internet suggests for reducing or avoiding the effects of the lachrymatory factor. Here's what I tried:

Method #1: Chill or slightly freeze the onions before cutting, the idea being that this will change the chemical reactions and reduce the gas that is released.
Result: The onion from the fridge has me crying just as quickly as room temperature ones. The one that was in a freezer for 30 minutes leaves me dry-eyed for a bit, but by the time I'm done dicing my eyes start to burn a little.

Method #2: Cut fast! Get the chopping over with before the gas reaches your eyes.
Result: Just hacking away at the onion, I get in the frying pan without so much as a sting in my eyes. The onion looks awful, though. Doing a proper dice, I take a little too long and start tearing up. If you don't mind a mangled onion, this is the way to go.

Method #3: Put a slice of bread in your mouth, and cut the onion with most of the bread sticking out to "catch" the fumes.
Result: It seems the loaf of bread I have has gone stale. I stop the experiment and put bread on my shopping list.

Method #4: Chew gum while chopping. It keeps you breathing through your mouth, which keeps the fumes away from your eyes.
Result: This seems to work pretty well as long as you hold your head in the right position. Leaning toward the cutting board or looking right down at the onion puts your eyes right in the line of fire again.

Method #5: Cut the onions under running water. This prevents the gas from traveling up into the eyes.
Result: An onion in the sink is a hard onion to cut. I think Confucius said that. My leaky Brita filter is spraying me in the face and I'm terrified I'm going to cut myself, but I'm certainly not crying.

Method #6: Wear goggles.
Result: In an effort to maintain my dignity, I try my eyeglasses and sunglasses first. Neither do me any good. The ol' chemistry lab safety glasses make me look silly, but help a little more. I imagine swim goggles would really do the trick, but I don't have any.

Method #7: Change your onion. "Tear free" onions have been developed in the UK via special breeding and in New Zealand via "gene silencing" techniques.
Result: My nearest grocery store, Whole Foods, doesn't sell genetically modified produce or onions from England. Tonight, we eat leeks!

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The Science Behind Why We Crave Loud and Crunchy Foods

A number of years ago, food giant Unilever polled consumers asking how the company might improve their popular line of Magnum ice cream bars. The problem, respondents said, was that the chocolate coating of the bars tended to fall off too quickly, creating blotches of sticky goo on carpeting. Unilever reacted by changing the recipe to make the chocolate less prone to spills.

When they tested the new and improved product, they expected a warm reception. Instead, they got more complaints than before. While the updated bar didn’t make a mess, it also didn’t make the distinctive crackle that its fans had grown accustomed to. Deprived of hearing the coating collapse and crumble, the experience of eating the ice cream was fundamentally changed. And not for the better.

Smell and taste researcher Alan Hirsch, M.D. refers to it as the “music of mastication,” an auditory accompaniment to the sensory stimulus of eating. “For non-gustatory, non-olfactory stimulation, people prefer crunchiness,” he tells Mental Floss. Humans love crunchy, noisy snacks, that loud rattling that travels to our inner ear via air and bone conduction and helps us identify what it is we’re consuming. Depending on the snack, the noise can reach 63 decibels. (Normal conversations are around 60 dB; rustling leaves, 20 dB.)

When we hear it, we eat more. When we don’t—as in the case of Magnum bars, or a soggy, muted potato chip—we resort to other senses, looking at our food with doubt or sniffing it for signs of expiration. Psychologically, our lust for crispy sustenance is baked in. But why is it so satisfying to create a cacophony of crunch? And if we love it so much, why do some of us actually grow agitated and even aggressive when we hear someone loudly chomping away? It turns out there’s a lot more to eating with our ears than you might have heard.


The science of crunch has long intrigued Charles Spence, Ph.D., a gastrophysicist and professor of experimental psychology and head of the Crossmodal Research Laboratory at the University of Oxford. Food companies have enlisted him and consulted his research across the spectrum of ingestion, from packaging to shapes to the sound chips make rustling around in grocery carts.

“We’re not born liking noisy foods,” he tells Mental Floss. “Noise doesn’t give a benefit in terms of nutrition. But we don’t like soggy crisps even if they taste the same. Missing the sound is important.”

In 2003, Spence decided to investigate the sonic appeal of chips in a formal setting. To keep a semblance of control, he selected Pringles, which are baked uniformly—a single Pringle doesn't offer any significant difference in size, thickness, or crunch from another. He asked 20 research subjects to bite into 180 Pringles (about two cans) while seated in a soundproof booth in front of a microphone. The sound of their crunching was looped back into a pair of headphones.

After consuming the cans, they were asked if they perceived any difference in freshness or crispness from one Pringle to another. What they didn’t know was that Spence had been playing with the feedback in their headphones, raising or lowering the volume of their noisy crunching [PDF]. At loud volumes, the chips were reported to be fresher; chips ingested while listening at low volume were thought to have been sitting out longer and seemed softer. The duplicitous sounds resulted in a radical difference in chip perception. It may have been a small study, but in the virtually non-existent field of sonic chip research, it was groundbreaking.

A view inside a potato chip bag

For Spence, the results speak to what he considers the inherent appeal of crunchy foods. “Noisy foods correlate with freshness,” he says. “The fresher the produce, like apples, celery, or lettuce, the more vitamins and nutrients it’s retained. It’s telling us what’s in the food.”

Naturally, this signal becomes slightly misguided when it reinforces the quality of a potato chip, a processed slab of empty calories. But Spence has a theory on this, too: “The brain likes fat in food, but it’s not so good at detecting it through our mouths. Noisy foods are certainly fattier on average.”

Fatty or fresh, raising decibels while eating may also have roots in less appetizing behaviors. For our ancestors who ate insects, the crunch of a hard-bodied cricket symbolized nourishment. In a primal way, violently mincing food with our teeth could also be a way to vent and dilute aggression. “There are some psychoanalytic theories related to crunchiness and aggressive behavior,” Hirsch says. “When you bite into ice or potato chips, you’re sublimating that in a healthy way.”


All of these factors explain why crunch appeals to us. But is it actually affecting what we taste?

Yes—but maybe not the way you’d think. “Sound affects the experience of food,” Spence says. “The noise draws attention to the mouth in the way something silent does not. If you’re eating pâté, your attention can drift elsewhere, to a television or to a dining companion. But a crunch will draw your attention to what you’re eating, making you concentrate on it. Noisy foods make you think about them.”

That crunch can also influence how much food we consume. Because noisy foods tend to be fatty, Spence says, they’ll retain their flavor longer. And because the noise reinforces our idea of what we’re eating, it affords us a sense of security that allows us to keep consuming without having to look at our snack—not so important in a brightly-lit room, but crucial if we’re in a dark movie theater. “It becomes more important when you can’t see what you’re eating,” Spence says.

Thanks to this hard-wired feedback, the snack industry has made it a priority to emphasize the sounds of their foods in both development and marketing. In the 1980s, Frito-Lay funded extensive work at a Dallas plant that involved $40,000 chewing simulators. There, they discovered the ideal breaking point for a chip was four pounds per square inch (PSI), just a fraction of what we might need to tear into a steak (150 to 200 PSI). The quality and consistency of the potatoes themselves is also key, according to Herbert Stone, Ph.D., a food scientist who has worked with companies on product development. “Too thick, too hard, and people don’t like them,” Stone tells Mental Floss. “Too thin and they just crumble.”

The right potato sliced at the right thickness with the right oil at the right temperature results in a solid chip—one resilient enough to make for a satisfying break when it hits your molars, but vanishing so quickly that your brain and body haven’t even processed the calories you’ve just taken in. “If they pick it up and put it in the mouth and the crunch is not what they expect, they might put it down,” Stone says. “It’s about expectation.”

A shopper examines a bag of potato chips

Walk down the snack aisle in your local supermarket or glance at commercials and you’ll find no shortage of claims about products being the boldest, crunchiest chip available. For years, Frito-Lay marketed Cheetos as “the cheese that goes crunch!” Even cereals try to capitalize on the fervor, making mascots—Snap, Crackle, and Pop—out of the sound their Rice Krispies make when submerged in milk. One ad for a brand of crisps drew attention for “cracking” the viewer’s television screen.

For most consumers, the promise of sonic flavor will draw their attention. But for a small number of people diagnosed with a condition dubbed misophonia, the sound of a co-worker or partner crunching on chips isn’t at all pleasurable. It’s insufferable.


According to Connecticut audiologist Natan Bauman, M.D., the average noise level of someone masticating a potato chip is between 25 to 35 decibels. (Other sources peg it as closer to 63 dB when you're chewing on a chip with your mouth open, or 55 dB with your lips closed.) When you hear your own chewing, the sound is being conducted both via the air and your own bones, giving it a distinctively unique sound. (Like talking, hearing yourself chewing on a recording might be troubling.)

For someone suffering from misophonia, or the literal hatred of specific sounds, it's not their own chomping that's the problem. It's everyone else's.

When we chew, Bauman says, the auditory cortical and limbic system areas of our brain are lighting up, getting information about freshness and texture. But people with misophonia aren’t struggling with their own sounds. Instead, they're affected by others typing, clicking pens, or, more often, chewing. The sound of someone snacking is routed from the cochlea, or cavity in the inner ear, and becomes an electric signal that winds up in the brain’s amygdala, which processes fear and pleasure. That's true for everyone, but in misophonics, it lands with a thud. They’ve likely developed a trigger, or negative association, with the sounds stemming from an incident in childhood.

“If you are scolded by a parent and they happen to be eating, or smacking, it becomes negative reinforcement,” Bauman says. Chewing, lip smacking, and even breathing become intolerable for sufferers, who often feel agitated and nervous, with corresponding increases in heart rate. Some fly into a rage.

Misophonics don’t necessarily recoil at all of these sounds all of the time: It may depend on who’s doing the snacking. Often, it’s a co-worker, spouse, or family member munching away that prompts a response. Fearing they’ll damage that relationship, sufferers tend to vent online. The misophonia subreddit is home to threads with titles like “And the popcorn eater sits RIGHT next to me on the plane” and “Chips can go f-ck themselves.” (The entire content of the latter: “F-ck chips, man. That is all.”)

Bauman says misophonia can be treated using cognitive therapy. An earpiece can provide white noise to reduce trigger sounds while sufferers try to retrain their brain to tolerate the noises. But even the sight of a bag of chips can be enough to send them scrambling.

People with misophonia might also want to exercise caution when traveling. Although some Asian cultures minimize crunchy snacks because loud snacking is considered impolite, other parts of the world can produce noisier mealtimes. “In parts of Asia, you show appreciation for food by slurping,” Spence says. Slurping is even associated with a more intense flavor experience, particularly when it’s in the setting of a comparatively quiet dining establishment.

Western culture favors noisier restaurants, and there’s a good reason for that. Supposedly Hard Rock Café has mastered the art of playing loud and fast music, resulting in patrons who talked less, ate faster, and left more quickly, allowing operators to turn over tables more times in an evening.

Spence believes sound will continue to be important to gastronomy, to chefs, and to food companies looking to sell consumers on a complete experience. Snack shelves are now full of air-puffed offerings like 3-D Doritos and Pop Chips that create pillows of taste. With less volume, you’ll snack more and crunch for longer periods.

A woman snacks on a chip

But the sound of the chip is just one part of the equation. The way a bag feels when you pick it up at the store, the aroma that wafts out when you first open the bag, the concentration of flavor from the granules of seasoning on your fingers—it’s all very carefully conducted to appeal to our preferences.

“When we hear the rattle of crisps, it may encourage people to start salivating, like Pavlov’s dogs,” Spence says, referring to the Russian scientist who trained his canines to salivate when he made a certain sound. We’re conditioned to anticipate the flavor and enjoyment of chips as soon as we pick up a package. Even hearing or saying the words crispy and crunchy can prime us for the experience.

When we’re deprived of that auditory cue, we can get annoyed. After news reports emerged that Pepsi CEO Indra Nooyi had mentioned her company might consider a quieter version of Doritos for women—an idea PepsiCo later denied they would label in a gender-specific fashion—women Doritos enthusiasts rallied around the Texas state capitol, condemning the perceived gender discrimination. To protest the possible dilution of their favorite snack, they made a spectacle of crunching Doritos as loudly as they could.


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