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Sugar, honey, listen up. Humans love the sweet taste of sweetness, but have you ever wondered why? What's the evolutionary purpose behind our love for sweets? Why can we taste sweet anyway? What are those sugar substitutes really made of? And will this diet cola give me cancer?
Hank and SciShow have the answers!

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The whole world is a Wonka factory. Nature has blessed us with a tantalizing smorgasbord of sweet treats and the right kind of tongues with which to taste them and oh, how we enjoy it.

Traditionally sweetness wasn't a huge part of the human eating experience and in some part of the world like, say, the Arctic, it was exceedingly rare. Yes, humans have always prized whatever fruits, berries, or honey they could gather, but most of those things were only available seasonally, if at all. But oh, how times have changed...

These days you can come in from mowing a lawn on a hot day and grab a soda sweetened with any number of things from agave to aspartame. Or just plain sugar!

So why do we have so many choices? What are they made of and will the diet cola give you the cancer? SciShow has the answer!

So you've got your tongue (at least, I hope you do) and it's covered with tons of lingual papillae, commonly known as 'taste buds', which are what make eating so enjoyable. Taste buds are chemoreceptors, which means that they translate the biochemical make up of food into electrical signals so the brain knows what it's tasting. Each taste bud is made up of clumps of 50 to 100 taste cells, proteins that bind with food molecules to allow us to detect specific flavors. In general, humans tend to go for salty and sweet stuff and avoid overly bitter and sour tastes. Probably because in nature those tastes often indicate that a potential food is poisonous.

Physiologically, the body associates sweet taste with high calorie and therefore high energy foods. It's desirable!

Most animals in the world can enjoy sweetness as well with the exception of those in the cat family. Cats can't taste sugar because they lack the genes that generate the sweet receptors. Perhaps because they evolved to only eat meat. Makes me feel kind of sorry for 'em.

But of course we humans can't get enough of sweet, and we've got the dental, diabetes, and obesity issues to prove it.

Not only can we taste sweetness, but we are connoisseurs of its delicate range of flavors from the honey, agave, and maple syrup to fructose and glucose and plants and fruits and good old sugar-bowl sucrose, as well as more recent adaptations like high fructose corn syrup and the host of artificial sweeteners on the market. We can taste them all and, we can tell them apart.

Natural sugars trigger our taste buds immediately, filling our senses with all kinds of goodness before gently fading away without leaving any after taste. Chemically, it's a beautifully simple process, but it is maddeningly elusive to duplicate, which is why synthesizing the taste of real sugar has become a sort of holy grail quest for food chemists. So far no one, in my opinion anyway, has even come close.

That's because when you lick that beautiful powdered sugar off your fingers the sucrose molecules act like a key that unlock a sweet sensation on your tongue, and then your brain. Meanwhile, your digestive enzymes start metabolizing that sucrose, giving you energy to move around and do your happy dance. Of course, if you don't use all that energy it sticks around as fat.

Artificial compounds affect our taste buds in a similar way to natural sweeteners, but because their molecules are structured differently, they bind to our receptors much more aggressively. And so their sweetness comes across not as a gentle flavor fairy kiss so much as a slap in the tongue. Which is why saccharin tastes about 300 times sweeter than plain sucrose and can leave a metallic-like after taste.

Interestingly most other animals are unable to taste these artificial sweeteners because their taste buds are set up differently. Each artificial sweetener has a different molecular shape, so each binds to our taste receptors in a distinct way, giving a signature flavor to their unnatural sweetness. That's why a typical diner will have a colorful display of different packets ready to sweeten your coffee.

And one thing almost all of these lab created sweeteners have in common is that they don't contain any calories or energy because our bodies cannot metabolize them. So they just slide through your guts without being absorbed. Some kinds are low-calorie but they're so bonker-sweet they just a dab'll do you so even if they are metabolized, its caloric pay-off is negligible.

So now let's take a quick look at what's going on in that table ramikin-rainbow. First, we got your average Joe packet of white sugar-bowl sugar, or sucrose. This white stuff is either refined from sugar cane or sugar beets, and there is no way to tell which it was by the time it reaches the packet phase, but it is chemically the same thing.

If you're in like a new-fangled hippie café, there may be a green packet in the mix: that's stevia, the new guy. Stevia is derived from the sweet-leafed stevia plant, a perennial shrub native to Paraguay and Brazil. The stevioside compounds that make its leaves sweet can be isolated and refined into an intense powder. Stevia is calorie-free, because our bodies can't metabolize it, just like the synthetics. This makes it very low on the glycemic index, meaning it doesn't raise your blood sugar, even though it's 300 times sweeter than sugar, so they have to actually cut it with other stuff. While South Americans have been using stevia for ages, it's pretty new to the US market and only recently did the FDA approve it as a food additive. 

Now if you're sitting at the table drinking coffee with your grandad, you might see him reach for a pink packet of saccharin. The first and oldest of all the artificial sweeteners, saccharin was accidentally discovered in the late 1870s by a chemist working with coal-tar derivatives. One day he forgot to wash his hands, and noticed that night at dinner that his fingers tasted sweet. This is going to be a repeated story throughout this episode. Teddy Roosevelt was a big fan of saccharin, and it gained popularity during WWI when sugar was scarce. In 1957, it was branded as Sweet'N Low. 

If you're old enough to remember your mom drinking cans of Tab soda, you may remember anything containing saccharin used to come with a warning label declaring that it may cause cancer. A bunch of lab tests in the 1970s linked saccharin to bladder and other cancers in rats, and the FDA tried to ban the stuff in 1977, but Congress intervened and suggested that it carry a warning label instead. Which hardly kept people from drinking it; after extensive lobbying from the diet food industry and sufficient claims that earlier studies were flawed, the label was removed in 2000. It's still the same compound, though, so it's more or less up to you to decide what you make of all that. 

Next to the pink come the blue sachets of aspartame. It was discovered in the 1960s when, yes, another chemist absentmindedly licked his finger to grab a piece of paper while testing a new ulcer medication. Thank you, sloppy chemical technique. Aspartame popped up in products in the early 1980s as an alternative to saccharin. It's about 200 times sweeter than sugar and unlike other synthetics, our bodies can metabolize it, so it does have a few calories. Once digested, aspartame breaks down into three components: the amino acid phenylalanine and aspartic acid as well as methanol, which is better known as wood alcohol. 

And finally, you have that sunny yellow sucralose. Sucralose was originally marketed as tasting like sugar cause it's made from sugar, and it is — it's made by reacting sucralose with chlorine: a toxic chemical. It, too, was accidentally created in the mid 1970s in London. A student and his advisor were working on a new DDT-like insecticide by slowly adding the toxic chemical sulfuryl chloride to a sugar solution. The resulting reaction formed a new compound: tetradeoxygalactosucrose. Then, as legend has it, the student was told to test the product, but misheard, and tasted it instead. It was crazy sweet; it was sucralose.

To make sucralose, you have to replace some of the oxygen and hydrogen groups in a sucralose molecule with chlorine atoms, at which point it isn't sugar anymore. But it is 600 times sweeter. Those chlorine particles prevent us from metabolizing sucralose, making it calorie-free, and it also makes the molecules heat-resistant enough to be used in baking, something other artificial sweeteners can't handle. 

Maybe by now you're wondering about the potential risks you've heard associated with artificial sweeteners. So...are they safe? Or what? Well first, remember that anything you buy at the grocery store to sprinkle on your cereal has been tested and approved, and is regulated by the FDA as being safe...enough. Even if it uses toxic chemicals in the processing, it's not a toxic chemical itself. However, a lot of people are still wary of these lab creations, including some of the researchers that make them. Critics argue that these products haven't been around long enough to truly measure the cumulative effects of a lifetime of consumption. Some new studies are suggesting that certain products may not be as benign as we once thought. A European Union funded study published in 2010, for instance, found that pregnant women who drank diet sodas appeared to be at greater risk of premature birth, while other research on aspartame linked it to several types of cancer in rats. And yet other studies have found that daily diet soda intake substantially increased the risk of type 2 diabetes. And that's one of the potential health effects that's getting a lot of attention these days.

Specifically, researchers are looking at how artificial sweeteners can interfere with the brain's natural ability to count calories, which can actually lead to weight gain. I mentioned before that the tongue and brain associate sweet things with calories, which are straight-up energy. The brain knows how many calories the body needs to get by, so it understands that a) a banana tastes sweet, and b) it gives a certain amount of energy to keep me satiated for a certain period of time, so I can stop eating now. But the theory is that artificial sweeteners are basically dirty rotten liars when it comes to your brain. Guzzling a gallon of diet soda only retrains your body to stop associating sweetness with calories. Pretty soon, you're eating that banana again, and the brain underestimates the true calorie count of said banana, and wants to keep eating.

One study found that rats fed artificially sweetened yogurt with their normal rat chow gained more weight than those eating sugar-sweetened yogurt. It was like the artificial sweeteners were deprogramming the animal's natural ability to keep tabs of its calorie intake. Your brain is used to associating sweetness with calories and calories with satiation; sweetness without calories can confound the brain and potentially lead to more craving and overeating. We may fool our tongues, but we can't fool our brains. So in the end it's up to you what you want to put in your body, but any way you swing it, moderation seems to be the key. 

 Ending Dialogue

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