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Despite some bold claims, most supplements can’t really "boost" your metabolism, and the actual changes we can make to it are pretty limited.

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Hosted by: Stefan Chin

#SciShow #Metabolism #STEM #Health

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Determinants of inter-specific variation in basal metabolic rate (2013)
Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure (2010)

Metabolism and weight loss - Mayo Clinic

Insulin and Insulin Resistance
New Insights into the Interaction of Carbohydrate and Fat Metabolism During Exercise (2014)

Water-Induced Thermogenesis (2003)

High-Intensity Interval Resistance Training (HIRT) influences resting energy expenditure and respiratory ratio in non-dieting individuals (2012)
Two minutes of sprint-interval exercise elicits 24-hr oxygen consumption similar to that of 30 min of continuous endurance exercise (2012)

Skeletal muscle metabolism (1990)
Contributing factors and variability of energy expenditure in non-obese, obese, and post-obese adolescents (2005)
Resistance training conserves fat-free mass and resting energy expenditure following weight loss (2008)

Non-exercise activity thermogenesis: The Crouching Tiger Hidden Dragon of Societal Weight Gain (2006)
Capsaicinoids and capsinoids. A potential role for weight management? A systematic review of the evidence (2012)
Dietary Capsaicin Reduces Obesity‐induced Insulin Resistance and Hepatic Steatosis in Obese Mice Fed a High‐fat Diet (2012)
The Effects of Capsaicin and Capsiate on Energy Balance: Critical Review and Meta-analyses of Studies in Humans (2011)
Can bioactive foods affect obesity? (2010)
The effect of green tea extract on fat oxidation at rest and during exercise: evidence of efficacy and proposed mechanisms (2013)
Effects of encapsulated green tea and Guarana extracts containing a mixture of epigallocatechin-3-gallate and caffeine on 24 h energy expenditure and fat oxidation in men (2005)
Long-term green tea extract supplementation does not affect fat absorption, resting energy expenditure, and body composition in adults (2015)
A moderate dose of caffeine ingestion does not change energy expenditure but decreases sleep time in physically active males: a double-blind randomized controlled trial (2013)
Effects of cigarette smoking and caffeine on REE (1994)

Sleep and metabolism: an overview (2010)


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[Scishow intro]

Stefan: Take a stroll into any nutrition store and you'll see displays stacked to the ceilings with products that claim to "boost" your metabolism.

Whether they're marketed as "Metabol Burn" or "VitaGainzzzz" or 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 it "boosts" your 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.

 (02:00) to (04:00)

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.

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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. 

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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.

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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: 

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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.

 Outro (11:56)

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