Moment 143: This Is Why You Can't Lose Weight: Daniel Lieberman

Steven Bartlett (0:03)

What are some of the other biggest myths within exercise that you've come across in writing this book?

Daniel Lieberman (0:10)

Gosh, there are so many. I had to actually limit it to 10 So I think if you want to understand physical activity and exercise, you also have to understand inactivity. And I think one of the biggest myths out there is that you need eight hours of sleep a night and that sitting is when you're smoking. You know, that basically, if you think about those two different myths, why is it that we're constantly told to sleep more and to sit less? Actually, it seems a little contradictory to me, right? And it turns out that let's take sitting first. So, you know, there are all these slogans like sitting is when you're smoking and it's really bad for you and every time you sit in your chair, you lose two hours of your life and whatever. It turns out that all animals sit, right? My dog sits, cows sit, chickens sit, every animal sits. And hunter-gatherers also sit. In fact, if you, some of my students actually put sensors on hunter-gatherers and we're doing some research in farmers as well. But they sit just as much as Westerners. So sitting is, there's nothing special about being, about today's life. It's sitting, it's that we sit all day long and don't do anything when we're not sitting, right? So if you, and furthermore, the big distance difference is not so much how much we sit, but how we sit. So it turns out that people who, if you get up every once in a while, right? Interrupted sitting is actually much more healthy than non-interrupted sitting for the same amount of time. So in other words, two people might, in the West, people sit for an average of about 40 minutes at about. Whereas hunter-gatherers, for example, or farmers in Africa where we work, get up every about 10, 15 minutes. When you do that, you actually, it's like turning on the engine of your car, you drive it around the block.

You're turning on all kinds of cellular mechanisms, you lower blood sugar levels, all kinds of genes get activated. And it turns out that that is by far the most important way to sit. So just get up every once in a while, just pee frequently, make a cup of tea, pet your dog, whatever.

Steven Bartlett (2:09)

Thinking when I'm on planes and I've got a long flight.

Daniel Lieberman (2:11)

I always sit in the aisle, right? So I can get up a lot, always.

Steven Bartlett (2:16)

What about sleep then?

Daniel Lieberman (2:18)

So sleep is another interesting one. So this idea that you need eight hours of sleep has been around for a long time. It's been around basically since the Industrial Revolution. But if you actually, so colleagues in my field, so in evolutionary medicine, have put sensors on people who don't have all the things that we're told have destroyed sleep. So think about it, we're told that TV and lights and our phones and all these things are are preventing us from sleeping, you know. Edison destroyed sleep, right? So so when you put sensors on people who don't have any electricity and they don't have TVs and they don't have phones and they don't have have any of these gadgetry, right? Electricity. It turns out they sleep like six to seven hours a night and they they don't nap. So this idea that natural human beings sleep eight hours a night is just is just nonsense. It's just not true.

And furthermore, when you start looking at the data, seven hours, if you actually look at if you graph sort of how many hours a night you sleep on the x-axis and sort of you know some outcome like cardiovascular disease or just how likely you are to die, it's kind of a u-shaped curve. So people don't get much sleep are in trouble. But the bottom of that curve is pretty much always about seven hours. So people actually do better if they sleep seven hours rather than eight hours. And yet we're told that if you don't sleep eight hours, there's something wrong, right?

Steven Bartlett (3:42)

Oh, so you can oversleep.

Daniel Lieberman (3:44)

Well, yeah. I mean, there's also some complexity to this too, because of course people who are ill might be sleeping more. And so there's some biases that creep into how you analyze the data. But basically it turns out that seven is for most people optimal, but there's a lot of variation, right? Teenagers sleep more, older people sleep less, it's complicated.

Steven Bartlett (4:03)