I wrote my first book 10 years ago. Since, I’ve been working on this one, The Human Diet.

As I work to turn a decade of research and thousands of pages of notes into a book, I’ve decided to release some chapters, maybe all of them. I’d love to have you join the community of early readers and critiquers.

To read The Human Diet first and get other exclusives, you just need to subscribe to my free Saturday 7 newsletter where I’ll announce and post the chapters.

Without further ado…The Human Diet.

The Human Diet

Introduction

It was awkward.

The waiter placed a big bowl in front of Katie. It was filled with lettuce, topped with tomatoes and croutons. Next to it, a ramekin of Italian dressing and a side of vegetable soup: leafy greens, broccoli, and tofu floating in a cream-based slurry. Then came Kevin’s food. A 24-ounce steak. No sides.

As the waiter left, Katie drizzled some dressing over her salad. Kevin stopped her.

“Are you going to use all that?”

“I was going to. Want some for your steak?” Katie offered.

“No. No. It’s just…”

“What?”

Kevin hesitated. Should he? He knew it was a bad idea. But he couldn’t stop himself.

“It’s just…it’s just that the dressing is basically seed oils and sugar. It’s ultra-processed junk. And you being a nutritionist and all…it just surprised me you’d eat that.”

The words hit like a blow to the gut. He undermined her intelligence and her credentials in a single breath.

“Ultra-processed junk?” she repeated, eyebrows lifted. “The oil is healthy fat. It’s polyunsaturated. And the brain needs sugar. It’s also good for the thyroid and reduces the stress hormone cortisol.” And good thing, she thought, because my cortisol levels are starting to rise.

Kevin, realizing he’d struck a nerve, decided to keep his mouth shut.

He cut his steak down the middle. Purple. Perfect. He sliced the fatty corner of the ribeye and to Katie’s horror, put it in his mouth. Her jaw hung open, her eyes wide. “You eat the fat?” she asked.

“It’s the best part!” Kevin exclaimed, as if this were an understood universal truth.

Well, thought Katie, since he started it…

“I’m surprised. I know you’re just a dentist, but everyone knows saturated animal fat and cholesterol is bad for your heart.”

Kevin grinned. Both at her comment and at the situation. They had met at the gym, where their mutual passion for health and fitness had sparked this first date. Now it was going down in flames. For a second Kevin debated whether he should try to extinguish the fire. He decided to keep cooking. “This is the healthiest fat you can eat,” he said. “Saturated fat doesn’t ruin your mitochondria like your polyunsaturated fats there.” Kevin pointed at the dressing with his knife. “Further, this saturated fat and cholesterol fuel sex hormone production.”

Katie scoffed. You won’t be needing those hormones tonight. “Kevin, your meal is ridiculous. There’s no fiber, no plant nutrients at all.”

“The cow I’m eating ate those nutrients for me.”

“Interesting theory.”

Her sarcasm was as thick as Kevin’s steak.

He was grinning, savoring every bite. The tender hunk of red meat across from her clearly repulsed her.

“Look,” he explained. “I know you think I’m clogging my arteries, and you probably think this rare meat is dangerous. But guess what? That lettuce you’re eating is one of the riskiest, most highly recalled foods because of E. coli and listeria contamination. The tomatoes in your salad are full of lectins that damage your gut. Croutons? Can you say gluten? The cream soup—more seed oils. The leafy greens are full of oxalates. Broccoli, glucosinolates. And tofu, endocrine disruptors.”

“Is that all?”

“Nope.”

Katie laughed. “What else?”

“Well, your meal is just lacking in essential nutrition. Where’s your vitamin B12, K2, D3? No creatine, taurine, carnosine, carnitine—”

“At least I’m not constipated or getting scurvy,” interrupted Katie.

Kevin thought about saying I thought I smelled something but opted for an even worse retort.

“What about sarcopenia?”

K.O. That was the last straw. You can’t insinuate that a gym rat’s muscles are wasting away and come back from it. Katie, whose face was now redder than Kevin’s steak, dropped her fork. “See you at the gym,” she said coldly, getting up and rushing for the door.

Kevin continued eating. He figured Katie was better off anyway. Saved from the seed oils, the sugar, and the grains.

. . .

What’s a “Health Diet”?

This was a fictional Kevin. Not me, of course. But Katie and Kevin’s date is a microcosm of the nutrition world today.

Everyone disagrees with everyone on everything. What one expert swears is essential, another condemns as harmful. What’s considered healing by some is deemed toxic by others.

The only thing we can agree on is that “diet” is a four-letter word. Like religion and politics, you don’t bring it up in polite company. Especially if you want your date to last more than four minutes.

If you were to say that four-letter word out loud, if you were to ask a hundred people to define a healthy diet, you’d get a hundred different answers. A shame, because it might be the most important unanswered question in the world.

Health is everything. You can have a million problems in life until you have a health problem. Then you only have one. And most people aren’t healthy. Being overweight and taking prescription medications is the norm, not the exception. ^1,2 Most people want to do something about their health, evidenced by the fact that many try dieting at some point to stop or reverse their declining health and expanding waistlines.³ It’s the right step, but almost always in the wrong direction.

Nothing has a bigger impact on your health than what you eat. Well, besides sleep. But your diet even determines the quality of your sleep. So there’s no way around it. You have to get the diet part right if you want to be healthy. And who doesn’t?

While health is the engine upon which your life runs, your diet is the fuel. It provides the energy to pursue your dreams, live vibrantly, and love fully. Most people are filling their tank with bad fuel. It stalls the engine. Weighs you down. Limits life.

There’s no greater cost than ignorance about what constitutes a healthy diet. If health is everything and diet is the key to the ignition, then there’s no greater mystery to solve. When I discovered the answer was hiding right under my nose, I decided I had to write this book. But this isn’t the first book to attempt to solve this mystery.

Over two thousand years ago, Hippocrates, known as the “Father of Medicine,” wrote treatises on the importance of diet. He was credited for saying “Let food be thy medicine.”⁴ Since then, countless historic figures—from physicians to philosophers—have speculated on the mystery of a healthy diet to no avail. Or certainly to no consensus.

Despite the millennia of diet debates, not only do we lack consensus, but the divergence of opinions has never been greater. In recent history, with human health deteriorating ever more quickly, it’s become a mainstream issue, evidenced by the proliferation of competing bestseller solutions.

In 1918, Dr. Lulu Hunt Peters published Diet and Health, which became the first book on diet to be a bestseller.⁵ By the 1970s and 1980s, as obesity rates took off, rapid-weight-loss books like The Complete Scarsdale Medical Diet and The Beverly Hills Diet topped the bestseller lists. But it wasn’t long before people realized quick-fix food restriction wasn’t a long-term solution. By the 1990s and 2000s, the focus shifted to macronutrients. Low-carbohydrate diets like The Atkins Diet competed against low-fat diets as recommended in The China Study, while The Zone Diet advocated for a balanced split of macronutrients. The following decade moved from “what” to eat to “when” to eat with calls for intermittent fasting dueling it out with guidance to eat every few hours, to boost your metabolism. Weight Watchers had you counting points, Jenny Craig counting calories, Atkins counting carbs.

These recommendations created more questions than answers. The only thing they had in common was their failure rates.

So what’s true? Is fat bad? Or was Katie right, and it’s just animal fats that are dangerous? Are seed oils really “heart healthy,” or was Kevin right, and they’re wrecking your metabolism? Should you just restrict all fat consumption, or eat a ketogenic diet of mostly fat?

Are carbohydrates the problem? Or are high-carb, plant-based diets best? Maybe it’s just the refined grains you need to avoid. The starchy nightshades. Or is sugar the problem?

Is protein the answer? Or is it aging you?

Does weight just come down to calories? Did everyone spontaneously lose all their willpower one day and start eating too many calories, making them fat and sick?

Perhaps the answer lies in a lack of a certain vitamin or mineral, one that the massive supplement industry somehow overlooked. Maybe it’s not food at all. Maybe you just don’t move enough, and you need to get outside and get more sun. Or is the sun dangerous…

Is there an Occam’s razor, or does the key lie in all the above?

There has been no shortage of theories and books. And so far, nothing has worked. At least not to the point of having anyone agree on anything yet.

Year after year, obesity and chronic disease keep hitting new all-time highs.^6,7 While the advent of antibiotics, reductions in infant mortality, and advances in medical care have expanded longevity, our health spans are getting shorter and shorter.⁸

Even though diet is a four-letter word, to me, it’s worth the risk to talk about.

Right now, I’m nearly one hundred percent certain that you and I don’t completely agree on what a “healthy diet” means. But right now, we can find common ground. We can agree that health is one of the most important things in your life and that diet plays a primary role in achieving and maintaining it.

So…where do we go from here?

. . .

A return to our roots

If we can’t reach a consensus, let’s go back to first principles, the most effective way to break down complicated problems. Returning to first principles involves stripping away layers of assumptions and conventions, cutting until we can cut no further. We dig our way to the root of fundamental truth. From there, we can rebuild understanding from the ground up.

This book cuts to the root of our evolutionary history. Then, step by step, builds The Human Diet.

This approach works because the first principles of all species’ diets are rooted in their evolutionary history. All animals compete in an evolutionary arms race. An organism adapts to its environment to optimize its survival and reproductive success. Selection shapes the body and molds the teeth to procure and process the food available. Through this process, an animal cultivates its species-specific diet. This dietary niche is intuitive and instinctual. Cows don’t need to be told to graze grass, nor orangutans to pick fruit, nor lions to prey on gazelles.

But we humans have lost this instinct. Left to our own devices, we eat food incongruent with our design and evolutionary past. To find our dietary roots, we need to work from first principles. This is the idea behind the paleo diet. However, while paleo has the right idea, it lacks the correct execution. Because there wasn’t just one paleo diet.

The Paleolithic period lasted for over 2.5 million years. And as you’ll read in Part I, “Early Human Diets,” our food selections—which have been widely misunderstood and misrepresented in modern diet literature—changed a lot between the onset and the end of the Paleolithic period.

Further, in the ten thousand years since then, humans have experienced genetic changes (as you’ll read in Part II, “Revolutionary Diets”). Just as the human dietary niche changed during the Paleolithic period, it also shifted afterward to adapt to our ever-evolving menu. The proof’s in your DNA, which speaks to the importance and potential place of non-paleo foods in The Human Diet.

The premise of the paleo diet is right. Humans, like all animals, have a species-specific diet. Where paleo falls short is defining what that entails. In Part III, “The Human Diet,” we’ll uncover the answer.

Because luckily, it’s written in your teeth.

. . .

The lost wisdom in your teeth

To return to our roots, there’s one place we must look. One fossil that rules them all. The only fossil that actually touches food.

Teeth.

Teeth are archaeological miracles. Even though people struggle to keep them for a single lifetime today, teeth endure for millions of years in the fossil record. They’re tiny time capsules, with every tooth telling a story. The thesis of this book is that your teeth tell you what to eat—you just have to listen to them. But I’m willing to bet that you haven’t always been paying attention.

My guess is you’ve had a cavity or two. It’s not just a lucky shot in the dark. Cavities are the most common disease in the world. Almost everyone has or will have them.⁹ I can say the same about crooked teeth and gum disease.^10,11 Our mouths are falling apart. The odds are that you even breathe wrong with it.

Just because dental problems are common doesn’t mean they’re normal. No other animals have the dental problems we have. In the wild, animals rarely develop cavities or crooked teeth or stop breathing in their sleep.

Likewise, that wasn’t true for our ancestors.

The fossil record shows that our ancient ancestors rarely developed cavities or crooked teeth.¹² They had robust jaws that accommodated all thirty-two chompers, including their wisdom teeth.¹³ Proper jaw growth also supported a big airway. Early humans didn’t have to worry about their snoring tipping off a tiger in search of a midnight snack.

Our ancestors didn’t have dentists, orthodontists, or sleep specialists. They didn’t even have toothbrushes. They didn’t need them.

This makes sense. Your teeth are critical to surviving, securing food, and nourishing your body. Over millions of years of evolutionary forces, Mother Nature in her infinite wisdom made sure your teeth were a marvel, stronger than steel, built to last. And last they do. Or should I say did. Today, even with special daily care, oral disease and degeneration run rampant.

In the scales of evolutionary biology, the downfall of our mouths has happened in the blink of an eye, on the latest pages of the human story. Why? That’s a mystery to most. But the answer is hiding right under your nose. Literally.

Your teeth are screaming at you. They’re telling you that there’s discordance: a mismatch between the foods you’re eating and the foods your teeth and jaws evolved to chew on. At the body’s entrance rages a crisis, a dental health epidemic that tells of a deeper problem. Oral disease is an early warning sign. It’s an alarm signaling an onslaught of health problems. However, few people are heeding that alarm—including dentists, who are too occupied with putting out fires to even look for the arsonist.

A diet that rots the hardest substance in your body isn’t just bad for your smile. It foretells of downstream consequences on your heart, your brain, and your overall health. An evolutionary perspective to diet can fix our oral health. And, consequently, resolve the other mounting health crises.

Teeth tell the story of our evolutionary history and the diets that shaped us. By rewinding the clock, we can get to the root and re-discover The Human Diet. It’s a biting history that unearths the wisdom lost in our teeth. To unravel the mystery, we have to journey back to where it all began—the very first human meal.

**********

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