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  • A lot of people think carbohydrates are the enemy.

  • The word might make you think of spaghetti, white bread, or other foods that'll supposedly

  • make you gain weight.

  • But dietary science is more complicated than that, and carbs are also found in fruits,

  • grains, vegetables, and milk.

  • They help you make and store energy, poop a little better, and are one of the three

  • classes of macronutrients that you need to live.

  • Chemically, carbs are pretty simple: just carbon, hydrogen, and oxygen.

  • Hence the name – “carbofor the carbons andhydratefor water.

  • But not all carbs are the same.

  • There are simple carbohydratesthe monosaccharides and disaccharidesand complex carbohydrates,

  • or polysaccharides.

  • These words just describe the structure of the moleculesso, monosaccharides are

  • the basic building blocks of longer carbohydrate chains.

  • Monosaccharides are also commonly called simple sugars, and taste sweet.

  • Like, you've probably heard of glucose.

  • We can thank plants for glucoseand, really, for most carbohydrates that we eatbecause

  • they convert carbon dioxide and water into glucose during photosynthesis.

  • There are also molecules like fructose, which is found in some fruits and honey, and galactose,

  • which is in milk.

  • All three of these molecules are isomers, so they have the same chemical formula, but

  • their atoms are arranged differently.

  • This gives them different chemical properties, like levels of sweetness.

  • Now, the taste of sugars is great, but carbs are really important because they're a great

  • source of energy.

  • Glucose metabolism is basically when glucose undergoes a bunch of chemical reactions in

  • cells to make these molecules called ATP.

  • And cells in your body use chemical energy from ATP to do pretty much everythingmove,

  • grow, especially keep your brain functioning.

  • So, monosaccharides are small enough to pass from your intestines into your bloodstream,

  • and then into different cells in your body that starts these energy-producing chemical

  • reactions.

  • But lots of the carbs we eat aren't plain old monosaccharides.

  • When two are bonded together, you get a disaccharidelike maltose, which makes cooked sweet

  • potatoes sweet, sucrose, which is table sugar, and lactose, the sugar in milk.

  • These have to be digested by enzymes before they can enter your bloodstream.

  • Some people can't break them all down, though, like if you're lactose-intolerant.

  • So bacteria might do it instead, which can make you feel all gassy and bloated.

  • And polysaccharides, or complex carbs, are just a bunch of monosaccharides bonded together.

  • Like, starch is a long chain of glucose molecules that plants use to store energy.

  • You have enzymes that can break down starch from foods like grains or potatoes, but it

  • takes a little longer to digest and absorb than monosaccharide-filled foods, like candy

  • bars.

  • On the other hand, we store extra glucose in the form of glycogen, mostly in our liver

  • and skeletal muscle cells.

  • See, there's this chemical produced by your pancreas called insulin that helps regulate

  • your blood sugar.

  • When you have too much glucose in your bloodstream, more insulin is released.

  • And it basically tells your body to start making glycogen, to store for later when you

  • need energy.

  • And glycogen is the reason that endurance athletes, like marathon runners, will sometimes

  • eat a bunch of carbs before exercising.

  • They're trying to store more glycogen, so when their body needs energy, their cells

  • can break those polysaccharides down and have lots of glucose to metabolize.

  • But here's the catch: you can only store so much.

  • And when your liver and skeletal muscle cells can't hold anymore, any extra glucose will

  • be converted into energy-dense fats for storage.

  • Sound familiar?

  • That fear that eating too many carbs makes you fat?

  • So that's why people might go on low-carb dietsto avoid making and storing more

  • fat molecules, even though eating carbs in moderation is not unhealthy.

  • If your body runs low on carbohydrate fuels, it'll start to metabolize these fats to

  • make energy instead.

  • There are different chemical reactions involved, and different byproducts get created.

  • But if you completely eliminate carbs from your diet, your body might not get enough

  • fiber, which is a group of compoundsincluding some complex carbohydratesthat we don't

  • have the enzymes to digest.

  • At first, that doesn't seem at all helpful, because we typically eat food to give our

  • bodies energy or chemical building blocks to make more stuff.

  • But some kinds of fiberlike cellulose, a polysaccharide that gives plants structural

  • supporthelp promote healthy bowel movements by adding bulk to your stool.

  • And other kinds of fiber can dissolve in water, forming a sludgy mixture that can reduce your

  • LDL cholesterol levelsthe kind that can build up in your bloodstream and be dangerous.

  • These fiber molecules bind to cholesterol and these chemicals called bile acidswhich

  • are made from cholesterolin your intestines, so you excrete them.

  • So fiber is your friend, and you shouldn't be afraid of carbohydrates.

  • They're important nutrients, can taste delicious, and give your body lots of energy.

  • But it is possible to have too much of a good thing.

  • Thank you for watching this episode of SciShow, which was brought to you by our patrons on

  • Patreon.

  • If you want to help support this show, you can go to patreon.com/scishow, and don't

  • forget to go to youtube.com/scishow and subscribe.

A lot of people think carbohydrates are the enemy.

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B2 中高級 美國腔

与碳水化合物的交易(The Deal with Carbs)

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    joey joey 發佈於 2021 年 05 月 06 日
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