Your body is a biological machine that follows the laws of thermodynamics and needs energy and raw materials to stay alive, which is why you eat.

The energy from food is measured in calories, and you need a certain amount to power your internal machines.

Your brain thinks, your heart pumps, your gut digests, your immune system immunes, and you contract your muscles to move around.

The harder a movement is, the more calories you burn.

An hour of walking burns about 260 calories, moderate swimming 430, biking 600, running 700.

If you eat more calories than you burn, your body stores them, mostly in the form of fat.

One kilogram or two pounds of fat is about 7,000 calories.

Seems simple.

To lose weight, you have to burn more than you eat, so fat is turned back into energy.

There are two ways to do this.

Eating less, which we'll cover in another video, and burning more, saved by moving around aimlessly, also called working out.

We also get told early on that exercising is healthy somehow, so working out should kill two birds with one stone.

Unfortunately, this doesn't exactly work out.

It's one of these frustrating experiences where you do what you think is right, only to not see the results you deserve.

In reality, exercising is a bad way to burn fat.

And, until recently, we fundamentally misunderstood what moving around a lot does to our bodies.

A few years ago, scientists began to compare populations in industrialized societies, which sit a lot, to hunter-gatherer communities, who move around a lot.

The Hadza people in Tanzania walk an average of 9 kilometers a day to find wild plants and hunt animals, dig for tubers, climb trees for honey, or collect water.

They can move more in a single day than an office worker in a week.

So, of course, they burn more calories, right?

But it turns out that the Hadza burn the same amount of calories per day as a typical person in an industrialized country.

Around 1,900 for women and around 2,600 for men, which doesn't make sense at all.

It's also not their genes, since it's the same for other hunter-gatherer tribes.

So the confused scientists looked at similar measurements in individual countries.

It got even stranger.

Active people who work out regularly do burn more than inactive people, but only very little, often as low as 100 calories, the equivalent of a single apple.

For some strange reason, the amount of calories you burn is pretty much unrelated to your lifestyle.

Per kilo of body weight, your body has a fixed calorie budget it wants to burn per day.

Sure, if you want to gain muscles by pumping iron, you also need to eat more to build and sustain them, or your new muscles wither away.

But in total, your body keeps your calorie budget per unit of you pretty stable.

And to make matters worse, if you want to lose fat, your body sabotages you in small and big ways.

First of all, when you begin to work out regularly, maybe going for a run in the morning, your body may subconsciously make you move less when you don't pay attention.

Maybe you take the elevator instead of the stairs, you sit more when you meet your friends, or you sleep longer, largely balancing out your burn again, preventing you from burning much fat.

You can overcome this temporarily.

If you do actually change your life after sitting around for years, and suddenly start working out without eating more, this is a shock to your system.

You actually do burn more calories and lose fat, so you can lose a few kilos or pounds through exercise.

But this is very short-lived.

Your body adapts and burns fewer and fewer extra calories each day, until it restores its original calorie budget.

After a few months, you burn basically the same amount you did when you didn't work out.

Bizarre.

And now we're getting to the actual reason why exercise is healthy.

Why your body is sabotaging you.

So your body has a hardwired activity budget per day that it wants to stick to.

This setting evolved when humans had to move a lot.

Not because they wanted to, but because they had to find food for survival.

But when food is abundant and exercise is voluntary, what does your body do with the energy that you're not using to move around?

We're simplifying a lot here, and this is relatively new science.

But in a nutshell, there are many different systems in your body trying to do their job as well as possible.

And if there's extra energy, they seem to use it.

Unfortunately, this is bad.

When your immune cells detect injuries or infections, they trigger inflammation.

Phytocells, alarm chemicals, and fluids flood into your tissue.

This is crucial, but it also causes damage, so it needs to be cleaned up quickly, or it can become chronic.

And chronic inflammation is one of the major contributors to many serious diseases, from cancer to heart failure.

If your immune system is on a tight budget, it has to be efficient with inflammation.

With lots of free calories, though, it overcommits.

Another thing is that your glands produce hormones you don't need, like cortisol, the stress hormone, which triggers your fight-or-flight response.

Crucial for survival, but if you have too much of it, you get, well, very stressed all the time.

Chronic stress is a major cause for a bouquet of health issues, including your mental state.

For our ancestors, who moved a lot and had to deal with sudden bursts of activity, fleeing from a lion, attacking that bison, this cortisol was crucial.

But if you live a modern, sedentary lifestyle, your body is ready for action that doesn't happen, hurting itself in the process.

Your body evolved to move regularly, and is fine-tuned to a certain base level of activity.

If this activity is missing, it still uses almost the identical amount of energy, just on stupid stuff.

This is why you burn almost the same amount of calories, whether you work out or not.

By working out, you're not doing anything extra, you're doing what your body is literally made to do.

Working out is not a magic bullet, but it seems to restore an internal physical balance that seriously affects your body.

And this is also why regular exercise is so incredibly healthy.

The evidence is incredibly clear here.

It reduces chronic inflammation and stress, it's good for your heart, may ease depression, and makes you live longer and better.

Movement is not really made to burn your fat, though.

Why humans are so hungry.

When your ancestors evolved, they had to work hard for calories.

Sometimes it would be easy and they could afford to chill out quite a bit.

But in hard times, they had to move quite a bit to feed themselves, walk longer to find prey, or dig longer to find tubers.

If extra movement burned more calories, this would lead to a spiral of starvation.

The less food you find, the more energy you need to find food, which doesn't even fill you up because you moved more.

It's like taking on more debt when you're in the red.

It works for a while, but then you go bankrupt and die.

So, for your ancestors, being able to move a lot without burning extra calories was a matter of life and death.

Okay, but this means the obesity epidemic of the modern world is not primarily caused by laziness, but by overeating.

Humans evolved to be mad for calories because of our extremely hungry brains and our extremely useless kids.

Kids are cute, but unlike other species, human kids have to be fed and cared for by adults for years before they become even remotely useful.

Because the human brain not only eats up about 20% of all our calories at rest, twice as much as our closest ape relatives, it also takes a lot of time to develop through playing, learning, and honing social skills, all the things that make us human.

Our species is so extremely calorie expensive to maintain that we became super efficient calorie harvesters.

Five hours of human hunter-gatherer foraging yields between 3,000 and 5,000 calories, while our ape relatives get no more than 1,500 at the same time.

And we became so good at calorie harvesting precisely because of our big brains and years of social skill training.

In a typical ancestral tribe, some members would spend the day searching for plants, others hunting or gathering honey, others nurturing kids.

And at the end of the day, we'd share the calories so that no one would end up hungry.

Being frenetic calorie harvesters seems to be deeply part of what makes us human.

It's not a bug, but a feature.

But today, it seems as if that feature has turned on us.

We can't stop overproducing food and overeating.

If you want to lose fat, food is the answer.

We'll cover diet in the next part.

So to conclude, you'll probably not lose nearly as much fat by working out as you hoped, but you will do something more important.

Give your body balance and make you more resilient, and prevent or delay many of the diseases that will make your life miserable so you can enjoy a higher quality of life for much longer.

But physical fitness is only half the equation.

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