The first foundation is this: Food is medicine, with both the power to heal and the power to harm. The best strategy for a long and healthy life is to eat your medicine — get your drugs at the farmacy, not the pharmacy! Food is far more than just calories or energy to fuel our bodies. It is information, instructions that regulate every function of our bodies in real time. Remarkable discoveries over the last few decades now enable us to use food not just for pleasure, joy, connection, and nourishment but also for rejuvenation, thriving, and even reversing disease. Quality and nutrient density are foundational to building a thriving human community. Some suggest we should all be nutrivores, prioritizing nutrient density; others propose we become qualitarians and focus on quality, no matter what dietary philosophy we hold. One discovery embodied in the Pegan Diet is that we are all unique, not just in terms of our preferences but also in our biology. Our genetic and biochemical uniqueness can guide us toward personalized nutrition. Despite our personal beliefs, some may thrive on a vegan diet; others may wither. Some become superhuman on a Paleo diet, and others not so much. The key is to explore your biology, not stay fixed in a particular ideology.

We are just beginning to understand how food influences our cells, tissues, organs, moods, thoughts, feelings, and the structure of our bodies, but what scientists have discovered over the last few decades is astonishing. Food is not only a source of energy, joy, connection, and pleasure; it can also rejuvenate us and even reverse disease. When we think of food, we think of protein, carbohydrates, fats, fiber, vitamins, and minerals. But the most important parts of food may be the tens of thousands of medicinal compounds embedded in plants and even animal foods that regulate, modulate, and influence nearly all of the 37 billion billion chemical reactions that occur in our bodies every second. I call this process symbiotic-​phytoadaptation. It means our bodies use chemicals found in food to beneficially influence each of our biological systems.

Through evolution, we have borrowed the molecular magic embedded in foods to optimize and supercharge our biology. For example, we can’t synthesize vitamin C or omega‑3 fats; we have to get these from nature. And it’s not just the obvious essential fatty acids, amino acids, and vitamins and minerals we get from our food; we also get important molecules called phytochemicals.

There are 25,000-plus phytochemicals in the plant kingdom identified to date, and they’ve only recently been deemed critical for health. Surprisingly they are also found in animals, such as in grass-fed cows, who consume a wide array of nutrient-dense plant foods. While deficiency of these phytochemicals may not result in an acute disease like scurvy or rickets or in protein malnutrition, it can lead to long- latency deficiency diseases such as heart disease, diabetes, hypertension, obesity, dementia, depression, and more.

The only way to take advantage of these disease-fighting compounds is to focus on our food quality. Deeply colorful plant foods, organic and grass-fed meats, and wild fatty fish are abundant in compounds that protect our cells and fight off invaders. If you eat industrial food, even vegetables, your diet will be depleted. Organic vegetables are more nutrient-dense. Factory-farmed cows fed a simplified diet of corn, cow poop, candy, and ground‑up animal parts produce meat that leads to inflammation and disease. Wild elk or regeneratively raised cows that forage on dozens of medical plants produce meat that has the opposite effect.

Every time you take a bite of food, consider that you are programming your biology for health or disease. When you eat healthy food, you are, in fact, eating medicine.

Excerpted from THE PEGAN DIET. Copyright © 2021 by Hyman Enterprises, LLC. Used with permission of Little, Brown Spark, an imprint of Little, Brown and Company. New York, NY. All rights reserved.


  • Dr. Mark Hyman is a practicing family physician and an internationally recognized leader, speaker, educator, and advocate in the field of Functional Medicine. He is the founder and director of The UltraWellness Center, the Head of Strategy and Innovation of the Cleveland Clinic Center for Functional Medicine, a 12-time New York Times best-selling author, and Board President for Clinical Affairs for The Institute for Functional Medicine. He is the host of one of the leading health podcasts, The Doctor’s Farmacy. Dr. Hyman is a regular medical contributor on several television shows and networks, including CBS This Morning, Today, Good Morning America, The View, and CNN. He is also an advisor and guest co-host on The Dr. Oz Show.