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We have this idea that if we want to lose weight, we join a gym on January 1st, we start
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working out regularly, and eventually we’ll slim down.
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Well, here’s some bad news. I read more than sixty studies on this, and
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it turns out exercise is actually pretty useless when it comes to weight loss.
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Dr. Kevin Hall at the National Institutes of Health has done some of the most important studies
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on exercise and weight loss We need to rebrand exercise … exercise isn’t
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a weight loss tool per se, it's excellent for health is probably the best single thing
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that you can do other than stopping smoking to improve your health.
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But don’t look at it as a weight loss tool. Exercise will definitely help you live a longer,
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happier life…. It’s just not the best way to lose weight. And the reason has to
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do with how our bodies use energy. You may not realize it, but physical activity
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is actually a tiny component of your daily energy burn.
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There are three main ways our bodies burn calories.
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These include your resting metabolism, so that's how much energy your body burns just
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for its basic functioning, just to keep you alive, basically.
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The other part of energy expenditure is the thermic effect of food, and that’s just
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how much energy is required to break food down in your body.
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The third part of energy expenditure is physical activity.
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For most people, physical activity - that’s any movement you do, only accounts for about
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10 to 30 percent of energy use. So the vast majority of energy or calories
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you burn every day comes from your basal or resting metabolism, over which you have very
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little control. While 100% of your “calories in” are up
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to you, only up to about 30% of your “calories out” are in your control.
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One study found that if a 200-pound man ran for an hour, 4 days a week for a month, he’d
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lose about 5 pounds at most, assuming everything else stays the same.
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And everything else doesn’t stay the same! Researchers have found we make all kinds of
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behavioral and physiological adaptations when we start increasing the amount of exercise
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we’re getting every day. For one thing, exercise tends to make people
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hungry. And I'm sure you know the feeling: you
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go for a spinning class in the morning, and then by the time you eat breakfast you're
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so hungry you maybe double the size of the portion of oatmeal you normally eat.
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There's also evidence to suggest that some people simply slow down after a work out,
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so if you went running in the morning you might be less inclined to take the stairs
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at work. These are called “compensatory behaviors”
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-- the various ways we unknowingly undermine our workouts.
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Researchers have also discovered a phenomenon called metabolic compensation. As people start to
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slim down, their resting metabolism can slow down.
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So the amount of energy you burn while at rest is lower.
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That means this bar might shrink as you start to lose weight.
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There’s still a lot of research to be done, but one study from 2012 is particularly interesting.
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They went out into the middle of the Savannah in Tanzania to measure the energy burn among
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a group of hunter gathers called the Hadza. These are super-active, lean hunter-gatherers.
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They’re not spending their days behind a computer at a desk.
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And what they found was shocking.
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What we found is that there was no difference at all.
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So even though the Hadza have a much more physically active lifestyle, they weren't burning any more
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calories every day than adults in the
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US and Europe. Somehow the energy they used for physical
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activity was being offset or conserved elsewhere. So how do they stay slim? They don’t overeat.
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We can undo the calories that we burn off in exercise pretty quickly.
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It would take about an hour of running to burn off a Big Mac and fries.
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You’d have to spend about an hour dancing pretty vigorously to burn off three glasses
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of wine you might drink with dinner. An hour of cycling really intensely on exercise
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bikes to burn off about two doughnuts. That’s why exercise is best seen as a healthy
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supplement for a strategy that’s focused on food.
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But despite extremely high obesity rates in the US, government agencies continue to present
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exercise as a solution ... as do companies with a real interest in
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making sure we keep eating and drinking their products.
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Since the 1920s, companies like Coca-Cola have been aligning themselves with the exercise
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message. The idea here is that you can drink all these
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extra bottles of soda as long as you work out. But as we're seeing, it doesn't work like that.
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Actually burning off those extra calories from a can of soda is really, really hard.
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We have an obesity problem in this country, and we shouldn't
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treat low physical activity and eating too many calories as equally responsible for it.
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Public health policymakers should really prioritize improving our food environment
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to help people make healthier choices about what they eat.
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It's not impossible to lose weight through exercise,
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it's just a lot harder. And we need to recognize how that works.
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If you do go to the gym, and you burn all these calories, it takes you a long time to do so
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and you put in a great amount of effort,
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you can erase all of that in five minutes of eating a slice of pizza.
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Relative magnitude is actually quite surprising, and most people don't fully appreciate that.