The 7 Big Lies About Exercise, Sleep, and Diet: A Fresh Look at Modern Health Myths

Modern life is a twisted game of contradiction: we’re more comfortable than ever, yet somehow feel more stressed, exhausted, and unhealthy. Enter Dr. Daniel Lieberman, Harvard professor and evolutionary biologist, ready to blow your mind and shake up everything you thought you knew about exercise, sleep, running, and, yes, even sugar. In his recent podcast, Lieberman lays bare some hard truths, debunks common health myths, and forces us to rethink our cushy, sedentary lifestyles.

Spoiler alert: We weren’t actually meant to spend our days sweating it out at the gym.

We Weren’t Meant to Exercise… Yet We Thrive on It

Here’s the kicker: Humans didn’t evolve to exercise. I know, I know, all those hours on the treadmill for nothing? Not exactly. While our ancestors weren’t hitting up spin class, they were active by necessity—hunting, gathering, and generally trying not to die. Lieberman explains that modern humans, despite not being hardwired for exercise in the way we think of it today, still reap massive benefits from physical activity.

So, why do we need it now? Because our cushy lifestyles—complete with comfy office chairs and Netflix marathons—have left our bodies confused. Our evolutionary biology craves movement. Even if exercise wasn’t designed into us, it’s now a lifeline, keeping our muscles, bones, and even our minds in check.

The Myth of 8 Hours of Sleep and the Demonization of Sitting

You’ve heard it your whole life: You need eight hours of sleep, or else. And sitting? Might as well call it the new smoking. Lieberman takes a sledgehammer to both of these ideas. He explains that eight hours of sleep is a modern construct, not some ancient biological necessity. In fact, in many traditional cultures, people don’t sleep in one big chunk at all. They nap, they doze, they adjust.

As for sitting, sure, the modern office setup isn’t exactly doing us any favors. But demonizing every minute you spend in a chair misses the point. It’s not sitting that’s the problem—it’s prolonged, unbroken sitting. Your body was made to move, but it’s also designed to rest. The balance, as always, is somewhere in between.

10,000 Steps? More Like 10,000 Marketing Gimmicks

Here’s one for the step-counting obsessives: That 10,000-step goal you’re religiously chasing? Completely arbitrary. According to Lieberman, it didn’t come from cutting-edge science, but from a Japanese marketing campaign in the 1960s. That's right: some clever marketer decided that 10,000 was a nice round number that sounded ambitious enough to sell a pedometer. And the world bought it—literally.

Now, does it mean that 10,000 steps a day won’t help you? Not necessarily. But the number isn’t a magic threshold. The point is to move more—whether you’re hitting 5,000 or 15,000 steps, any movement is better than none.

Age Is Just a Number (When It Comes to Activity)

Think it’s normal to slow down with age? Guess again. Lieberman debunks the idea that physical decline is an inevitable part of getting older. In fact, the less you move, the faster you age. It's a vicious cycle: we get tired, we move less, and our bodies deteriorate even quicker. What breaks the cycle? You guessed it—exercise.

This isn’t about marathon running at 90 (although, more power to you if that’s your thing). It’s about keeping your body in motion, keeping your muscles engaged, and staying active in ways that work for you. Getting older doesn’t mean you have to sit down and shut up. In fact, it’s the perfect time to ramp up.

Comfort Is Killing Us: How Convenience Created a Crisis

Here’s the uncomfortable truth: our obsession with comfort is slowly ruining us. Lieberman argues that modern life—with its endless conveniences—has created a disconnect between our biology and our lifestyle. We’ve engineered physical exertion right out of our daily routines. Food is easier to get, work is less physically demanding, and even our hobbies (hello, binge-watching) have become sedentary.

The result? We’re living in bodies that crave movement and challenge but find themselves stuck in a cushy, overly optimized world. Lieberman doesn’t mince words: if we don’t redesign our lives to incorporate more activity, we’re setting ourselves up for a host of preventable diseases—heart disease, cancer, diabetes—the works.

Sugar: Sweet Friend or Deadly Foe?

You’ve probably heard it a thousand times: sugar is evil. But Lieberman’s take is a little more nuanced. He acknowledges that excessive sugar consumption, especially in the context of our sedentary modern lives, is a huge problem. But he also points out that hunter-gatherer societies consumed natural sugars—like honey—and balanced it with high levels of physical activity. In other words, it’s not sugar itself that’s the problem; it’s the fact that we’re consuming it in massive quantities without moving our bodies.

And here’s a harsh reality check: No amount of exercise can completely undo the damage of a sugar-heavy diet. Exercise can help regulate insulin levels and reduce inflammation, but if you’re downing sugary snacks without changing your lifestyle, you’re fighting a losing battle.

Why Running Isn’t Killing Your Knees

Love it or hate it, running gets a bad rap, especially when it comes to knee injuries. But Lieberman debunks the myth that running is inherently bad for your knees. In fact, it’s not running itself, but how you’re running that’s the problem. Poor form, modern footwear, and overstriding are the real culprits behind those nagging injuries.

Lieberman advocates for a more natural, barefoot-style running technique—one that minimizes impact and reduces the risk of injury. It’s about working with your body’s natural biomechanics, not against them. So before you toss out your running shoes, consider refining your form instead.

The Real Key to Fitness: Compassion and Commitment

Fitness isn’t a one-size-fits-all endeavor. Lieberman stresses the importance of compassion—both for yourself and others. Fitness shouldn’t be about guilt, shame, or unrealistic expectations. It’s about finding what works for you, whether that’s a morning walk, a yoga class, or a dance party in your living room.

And let’s be real: the journey to fitness is a lifelong one. There’s no finish line, no “perfect” body or level of health to achieve. What matters is that you keep moving, keep trying, and find joy in the process. Because in the end, the only bad workout is the one you didn’t do.

Takeaways: Redesigning Your Life for Health and Happiness

Lieberman’s insights are both simple and profound: modern life, with all its comforts, has made us sicker and less active. But we don’t have to accept this as our fate. By redesigning our environments to encourage more activity, prioritizing movement over perfection, and finding compassion for ourselves along the way, we can bridge the gap between our biology and our modern world.

So get moving, but don’t stress about counting steps. Find what works for you, and remember: you weren’t born to exercise, but your body—and your future self—will thank you for it.