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  • Thanks to Brilliant for supporting this whole week of SciShow.

  • Go to Brilliant.org/SciShow to learn more.

  • [♪ INTRO]

  • Take a stroll into any nutrition store and you'll see displays

  • stacked to the ceilings with products that claim toboostyour metabolism.

  • Whether they're marketed asMetabol BurnorVitaGainzzzzor something equally

  • absurd,

  • there's one thing that they have in common: They don't really work.

  • Decades of research show that making any meaningful change in your metabolism

  • is really hard to do, so a powder or pill won't turn you into a calorie burning machine.

  • Most supplements can't really boost your metabolism,

  • and the actual changes we can make to it are pretty limited.

  • Contrary to what the supplements might lead you to believe,

  • metabolism isn't just the ability to burn off energy from food.

  • The actual claims are all over the place,

  • but in general when a product says itboostsyour metabolism,

  • that's code for burning more calories or fat.

  • Using calories is a part of metabolism,

  • but even that process is affected by your physiology, like enzymes and hormones.

  • When scientists talk about metabolism,

  • they use it as a broader term for all of a cell or body's processes.

  • Which is a pretty big concept, and not very informative on its own.

  • So since that's such a broad definition, researchers usually break it down into smaller components.

  • The biggest slice of the metabolic pie is something called basal metabolic rate,

  • or BMR, and it's the energy your body uses at rest.

  • But even that comes with an asterisk.

  • True BMR is measured when the subject is at rest, at a certain temperature,

  • not digesting food, and not pregnant, because all of those things

  • can nudge your energy consumption one way or the other.

  • Fun fact: growing a whole other human inside of you changes your energy needs.

  • Furthermore, different parts of the body have different metabolic rates.

  • Gram for gram, your kidneys and heart consume the most calories,

  • followed by your brain and liver.

  • Towards the bottom of that list is muscle and fat.

  • But no one is advocating taking on an extra kidney to try to raise your rate of calorie burn.

  • Instead, researchers focus on two tissues that we can tweak: fat and muscle.

  • Fat, or adipose tissue, is one of the ways your body stores energy long term,

  • so it makes sense that it doesn't take a lot of energy to store energy.

  • Muscle, on the other hand, has the opposite job.

  • When you exercise, it uses quite a bit of energy and oxygen,

  • but even at rest, its caloric needs are higher than fat.

  • And sure enough, people with a higher proportion of muscle mass

  • tend to have higher basal metabolic rates than people with more fat mass.

  • That is, they burn more calories per gram of body weight even when they're resting.

  • Now the second slice of the metabolic pie is energy used during exercise, but again, with an asterisk.

  • Yes, when you exercise, you use a few more calories for a short period of time,

  • but even a thirty minute workout burns a pretty small number of calories compared to your BMR.

  • So researchers also look at how exercise affects something called resting energy expenditure,

  • which is just a more relaxed way to measure overall metabolism than the super-specific BMR.

  • Multiple research groups have found that aerobic exercise,

  • whether it's long and slow like riding a stationary bike,

  • or short bursts of intense exercise like sprinting, all elevate metabolism temporarily after exercise.

  • Likewise, lifting weights also leaves you with a slightly boosted metabolism after the workout.

  • And long term, those bulkier muscles are probably what make the biggest difference in your metabolism.

  • One 2008 study on diet and exercise in overweight women found that resistance training

  • allowed participants to keep their metabolisms elevated even after the diet,

  • while the ones who just cut calories ended up slowing their metabolisms.

  • But even if you're not hitting the gym, you still have the third slice of the metabolic pie:

  • non-exercise activity thermogenesis, which makes for a neat acronym.

  • It encompasses all of your day-to-day, moving-around-but-not-exercising activities,

  • like walking around the house, or doing the dishes, or watering the plants.

  • That adds up to a good chunk of metabolism, but it varies a lot depending on your lifestyle.

  • Now this last way our bodies burn calories actually has a lot to do with how we eat calories.

  • It takes energy to digest, absorb, and get rid of food,

  • so we call those calories the thermic effect of food.

  • High-protein foods take a bit more work to digest than others,

  • so your steak has a higher thermic effect than a bag of chips.

  • But even something like ice water has a thermogenic effect

  • thanks to our bodies warming it up, which takes energy.

  • Now, it's easy to think of our meat sack bodies as simple calorie-burning engines,

  • but metabolism happens at the cellular level,

  • which is where supplements might claim their products work.

  • For instance, after eating and digesting a piece of fruit,

  • the simple sugar glucose is released into your bloodstream.

  • This is our bodies' main energy currency.

  • But it still needs to get into the cell so that cellular machinery can turn it into usable energy.

  • And it's a big molecule by cell standards, so it doesn't just seep right in.

  • Which is why our bodies produce insulin,

  • a hormone that binds to receptors on our cells and shuttles glucose inside of them.

  • Without insulin, we could still digest food and get glucose into our bloodstream,

  • but we wouldn't be able to process it into energy since it couldn't enter the cell,

  • which is exactly what happens in diabetes!

  • Your body either can't make enough insulin, or has trouble importing enough sugar into cells.

  • But glucose isn't the only nutrient our body uses for fuel.

  • And chances are that if a product is marketed as a metabolism booster,

  • it's concerned with one nutrient: fat.

  • Now, fat is utilized in a complex chain of chemical events that I'm not gonna explain here.

  • But at rest, your body typically doesn't use fat for energy.

  • That's supposed to be stored energy,

  • whereas the glucose that's floating in your blood is ready to use right away.

  • Before resorting to breaking down fat, your body will typically tap

  • the stored glucose in your muscles and liver, called glycogen.

  • And to complicate things further, your body never only uses fat or only glucose as a fuel source.

  • It's a mixture of both.

  • So hopefully you're starting to see that your metabolism has lots of moving pieces to it,

  • and if a product says it can change your metabolism, that's a pretty bold claim.

  • Despite the lack of evidence backing them, pharmacies still keep these products in stock,

  • even as some researchers have voiced concerns about their safety.

  • These products are available over the counter, at least in the US,

  • but they're not regulated as tightly as proper pharmaceuticals.

  • Now, there are a few ingredients that can increase resting energy expenditure,

  • but that doesn't mean a supplement will boost your metabolism long term.

  • Like capsaicin, the same molecule that gives red pepper its spiciness.

  • This ingredient has been used to suppress appetite in the past,

  • but it can also increase energy expenditure and shift your body towards burning fat.

  • It does this by kicking off a chain of events that eventually stimulates the sympathetic nervous system,

  • which is the same system that's activated during the fight or flight response.

  • This part of your nervous system is responsible for basic bodily functions

  • like regulating heart rate and basal metabolic rate.

  • So when we see a chemical that stimulates the sympathetic nervous system,

  • we generally associate that with an increase in metabolism.

  • When researchers looked into capsaicin,

  • they saw it activate a receptor called TRPV1, which is an important part of fat oxidation.

  • And it might also help you process glucose more efficiently by toning down

  • the inflammatory response often associated with obesity.

  • When used according to protocol,

  • capsaicin has the potential to help you burn an extra 50 calories a day;

  • that's according to a literature review published in 2012.

  • But whether you stick to protocol or not is a whole different issue.

  • Whether or not the subjects actually followed directions usually determined any metabolic results.

  • And as can be the case with diet and supplement research,

  • the dosage of capsaicin varies widely from study to study.

  • Some studies used pure capsaicin capsules as high as 150 milligrams,

  • while others sprinkled less than a milligram's worth of red pepper on someone's food.

  • Surprisingly though, this is consistent with how much variation there is in our diets.

  • The average capsaicin intake in Europe is 1.5 milligrams a day.

  • Meanwhile, in countries with spicier cuisines, like India or Mexico, it's anywhere from 25-200 mg.

  • Now another metabolism boosting ingredient that's present in most countries' diets is caffeine.

  • There's extensive data supporting caffeine's ability to raise energy expenditure,

  • and it's not because it keeps you awake and jittery all night.

  • Caffeine ends up stimulating the same sympathetic nervous system,

  • but through a different mechanism than capsaicin.

  • It also has the ability to activate an enzyme called lipase, which promotes the breakdown of fat.

  • And caffeine comes in many different forms, from pills to candy bars to coffee.

  • And despite all the other ingredients that manufacturers throw into energy drinks and

  • other caffeinated products,

  • caffeine seems to be the only one that does anything useful for metabolism.

  • A 2014 article from the journal Obesity reported that a commercially available energy drink

  • raised subjects' energy expenditures, but a regular mixture of water and caffeine did the same thing.

  • This suggests that all those other ingredients, usually some B vitamins,

  • don't have any noticeable effect in these products.

  • Plus, the increase in fat burning ability

  • might actually be canceled out if the caffeine interrupts your sleep.

  • One study in 2013 gave a moderate dose of caffeine

  • to young men who didn't normally consume that much.

  • And while their resting energy expenditures didn't change, they got less sleep.

  • Caffeine might be one of the reasons that our final ingredient,

  • green tea, is such a common ingredient in metabolism supplements as well.

  • Green tea extract is exactly what it sounds like: compounds taken from green tea.

  • That usually includes caffeine as well as a group of chemicals called catechins.

  • In cell, animal, and human studies, researchers have seen

  • increased resting energy expenditure after giving subjects doses of green tea.

  • One study back in 2005 gave participants capsules of EGCG, one of the green tea catechins,

  • with caffeine and saw an increase in energy expenditure of about 180 calories.

  • But the metabolic claims don't stop there.

  • Green tea supposedly helps bump up your fat burning too,

  • although there's not a lot of direct evidence in human studies to support it.

  • Supposedly, the catechins within green tea inhibit an enzyme that

  • degrades neurotransmitters like dopamine and epinephrine.

  • And just like capsaicin and caffeine, this means stimulation of the

  • sympathetic nervous system, which raises energy expenditure.

  • But it's also been implied from these studies that long term green tea use

  • might change our gene expression towards a slight bump in fat metabolism.

  • But again, we need more evidence from human studies.

  • At the same time, we're still trying to work out details on how to use it.

  • There are trials where researchers gave green tea extract to participants and saw no noteworthy results.

  • So all of these ingredients have some evidence to back them up,

  • but there's a big difference from experimental conditions to how you use the products at home.

  • Ultimately, one of the best metabolism boosters, other than increasing muscle mass,

  • is a totally free product that you won't see on any nutrition store shelves: sleep.

  • For decades, we've known that sleep deprivation can impair metabolism.

  • And it does this by messing around with certain hormones that control energy intake and storage.

  • Research published in 2010 hooked subjects up to a steady drip of glucose overnight

  • and cut their sleep to four hours per night for two nights,

  • and then had them sleep ten hours per night for another two nights.

  • And they found that ghrelin, a hormone that signals hunger, was increased by 28%,

  • while leptin, a hormone that signals fullness, dropped 18%,

  • even after the participants got two nights of make-up sleep.

  • This went along with an increase in appetite rating as well,

  • which you're probably familiar with if you've pulled an all-nighter.

  • Plus, sleep deprivation harms your insulin's ability to respond to glucose.

  • So while you might think you're more active while you're awake into the wee hours of the night,

  • you're doing your metabolism more harm than good.

  • So can those flashy products in nutrition stores actually boost your metabolism?

  • Well, there's some truth to their claims, but clearly, it's not that straightforward.

  • Some work in specific conditions, while some may actually be dangerous in large amounts.

  • And obviously, if you're thinking about trying any of these things, check with your doctor first.

  • On the other hand, if you feel like you're on a roll, and you wanna keep learning,

  • the folks at Brilliant have daily challenges to teach you something new every day.

  • Each day features new challenges covering everything from electricity to statistics.

  • And if you like a given challenge and want to learn more,

  • each one ties back to a related course covering the material in depth.

  • Brilliant.org has over 50 interactive courses and they're adding new ones all the time.

  • The challenges use animations, illustrations, and interactive visualizations

  • to guide you through and give you everything you need to arrive at the solution,

  • so you really are learning as you go along.

  • Daily Challenges are free, but if you're the kind of completionist who likes to finish everything,

  • signing up for a premium subscription gets you access to the entire archive.

  • And conveniently, the first 200 people to sign up at Brilliant.org/SciShow

  • will get 20% off the annual Premium subscription.

  • And best of all, by checking it out, you're supporting us as well, so thanks!

  • [♪ INTRO]

Thanks to Brilliant for supporting this whole week of SciShow.

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B2 中高級

大多數新陳代謝促進劑都是BS (Most Metabolism Boosters Are BS)

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    林宜悉 發佈於 2021 年 01 月 14 日
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