Spoiler alert! How ketones work is not how you think they work. With so many things, what’s old is new again. While the ketogenic, or “keto,” diet, has been around since the 1930s, there’s been a resurgence of interest in this high-fat, ultra-low-carb way of eating in the past few years. Talk to your friends, surf the internet, or scan the nutrition articles in your favorite magazine, and you’ll see many variations on the keto theme. There’s dirty keto, clean keto, calorie-restricted keto, high-protein keto, the Paleo/keto hybrid, keto cycling, protein-sparing keto, and even a lazy man’s version of this popular dietary regimen. Its proponents will tell you that this eating plan is life-changing — do keto “right,” whatever that means, and you’ll soon find yourself not only shedding unwanted weight quickly but improving your cholesterol, blood pressure, energy levels, and sleep quality in the process. Who wouldn’t want all that?

While each type of ketogenic diet has its own unique quirks, the premise of them all is basically the same—and, as it so happens, deceptively simple, and wrong. Keto experts will tell you that when you drastically reduce your carbohydrate intake and instead consume 80 percent of your daily calories from fat, your body shifts into a unique metabolic state called ketosis. In ketosis, the liver transforms fats into special molecules called ketones (sometimes referred to as ketone bodies), a so-called miraculous fuel source that can be used to power the body and brain instead of glucose that comes from carbs. The basic idea is that a ketogenic diet will make you an incredibly efficient fat burner, allowing you to rapidly lose weight and enjoy a host of other health benefits. Sounds great, right?

This very elementary explanation of ketosis (don’t worry, I’ll go into more detail in the following chapters) has been the presiding theory of why ketogenic diets, though challenging to maintain, are so beneficial to well-being. In my first book, The Plant Paradox, I even put forth my own keto-based intensive care program to help people boost mitochondrial function and improve their overall health in the process. It’s the diet I’ve been prescribing to my own patients for the past twenty-two years.

There’s only one problem: ketones are not the miraculous cellular fuel that so many of us thought they were. We now understand they actually aren’t a good fuel source at all. In fact, the entire theory of how ketones improve health is just plain wrong. That’s not to say ketones aren’t important. As I’ll explain in the following chapters, these little molecules play a vital role in helping to ease the burden of your mitochondria, your cells’ energy factories, in ways that can help prevent as well as reverse not only weight gain but also diseases of aging. Even more important? Once you learn what ketones really do, you’ll realize you don’t have to force yourself to eat a heavy, high-fat, and, frankly, boring diet to harness their power.

IT’S NOT WHAT YOU THINK

Ketones aren’t some special source of magic cellular fuel. Rather, they are vital signaling molecules that tell your mitochondria to get up, get moving, and start wasting calories. Our mitochondria produce fuel for our bodies by taking glucose, amino acids, and fatty acids from the foods we eat (which your gastrointestinal system has so kindly broken down from carbohydrates, proteins, and fats, respectively) and converting them into a special molecule called adenosine triphosphate (ATP), an energy “currency” our cells can actually spend.

But the latest research shows that mitochondria are involved with much, much more than just energy production. They play an integral role not just in survival, but longevity. Yet to truly understand what mitochondria do—and why ketones are produced, when they are produced, and their ultimate purpose—you need to let go of everything you thought you knew about keto.

If you’re familiar with The Plant Paradox or any of my other books, you likely know I’m famous (or perhaps infamous) for challenging people’s long-held beliefs about “healthy” foods. Disruption is in my nature. Even in my previous career as a heart surgeon, I pushed back on the way things had always been done, discovering new ways to protect my patients during open-heart surgery that are today considered best practices in care. Now, just like Mark Antony in Shakespeare’s famous play, I come not to praise keto, but to bury it — at least the conventional notions of the keto diet (or even most so-called healthy diets, for that matter).

The best part? When you understand the role of mitochondria and how they affect your metabolism, you no longer have to worry about fat percentages, macronutrient proportions, calories, or any other metrics. This new understanding provides a healthy path forward for folks like Janet, Miranda, and even all the people who have wanted to try a keto approach but couldn’t get past the fat requirements. And that’s because, as you will learn in the following chapters, the role of ketones in weight loss and health is not what you think—and harnessing their benefits doesn’t require you to consume massive amounts of saturated fats. Intrigued? Let’s get started.

Dr. Steven Gundry is one of the world’s top cardiothoracic surgeons and a pioneer in nutrition. He is the founder of Gundry MD, a line of wellness products and supplements, host top-rated health show, The Dr. Gundry Podcast, and medical director at The International Heart and Lung Institute Center for Restorative Medicine. He is the author of many New York Times bestselling books and he just released his new, highly anticipated book, Unlocking the Keto Code, which offers a revolutionary take on the keto diet that debunks common myths and shows readers how to reap the rewards of keto with less restriction.