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Sugar alcohol sounds like a fun adult dessert, but what is it really?

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If you made a list of all the substances that you most like to ingest, what would be on it?

Would sugar be on that list? Of course it would. Because sugar’s delicious! And how about alcohol? If you’re old enough to drink it, alcohol can be pretty OK, although it can turn on you pretty quickly.

But if you’ve looked at a nutrition label lately, you’ve probably noticed that there’s an ingredient showing up in a lot of foods that seem to combine these two: sugar alcohol. It’s a common ingredient in many processed foods. It’s used as a low-calorie sweetener in everything from soft drinks to snack bars, and there are lots of different kinds, like erythritol, xylitol, or sorbitol.

But, what is it? Is it sugar? Or is it alcohol? Is it the sugar that’s in alcohol? And if I see it on a nutrition label, does that mean that there’s booze in my protein bar or diet cola? No!

Sugar alcohol actually starts out as sugar, but then it’s fermented to create a kind of alcohol. But not the kind that you’re probably thinking of. Whenever you hear people talking about “alcohol”, like 99.99 percent of the time, what they’re talking about is ethanol, also known as ethyl alcohol.

But ethanol is just one of many kinds of alcohol. Technically speaking, an alcohol is any compound that contains a hydrogen-oxygen pair, known as a hydroxyl group, that’s bound to an atom of carbon that’s saturated, meaning all of its electrons are bound to something else. And that’s it!

That describes all kinds of chemical compounds, most of which you’d never want to put in your body. Like ethylene glycol, the stuff that’s in antifreeze? That’s an alcohol. And so is 2-propanol, aka isopropyl or rubbing alcohol.

Substances like these aren’t intoxicating, they’re just poisonous, usually because your body metabolizes them into some horrible, dangerous compound like formic acid or oxalic acid. So how do you take sugar and turn it into an alcohol, one that won’t kill you?

Well, most sugar alcohol, like erythritol, for example, is made from corn. The corn is boiled, mashed and broken down into its basic sugar, glucose. Then, it’s fed to a bunch of fungus.

Yeasts, to be precise. Because, sugar alcohol is the product of fermentation, just like the alcohol in beer or wine. To make sugar alcohols specifically, companies use certain kinds of yeast that turn glucose into sweet, non-toxic alcohols.

These yeasts eat away at the glucose, breaking down those big, clunky sugar molecules into smaller, simpler molecules. And what’s left are molecules with four carbons, each of which is saturated, and attached to a hydroxyl group. And there you have it.

Sugar. Alcohol. It doesn’t have the intoxicating effects of ethanol, and thankfully it also doesn’t have the killing-you effects of other alcohols, because your body doesn’t break it down into anything deadly.

But it does taste sweet, because like glucose, it bonds with the sweetness receptors on your tongue. And at the same time, it contains fewer calories than a molecule of glucose. That’s because most sugar alcohols pass through your body without being metabolized all the way.

In some cases, they’re not broken down at all. Erythritol, for example, is absorbed as a whole molecule right there in your small intestine. It’s never broken apart, so the energy in its bonds is never released. Which means it contains zero calories!

Sugar alcohols do have their downsides, though. Erythritol is excreted mostly through your urine, you just pee it out. But other kinds of sugar alcohols make it all the way through your intestines without being completely absorbed, and have to come out as the other kind of waste. Which is why foods that contain alcohols like sorbitol and mannitol warn you on their labels that they may create a “laxative effect.”

Which, I dunno, could be worse, I guess? So maybe you can have your cake and eat it too. It just might give you a little diarrhea.

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