Mark Hyman, M.D., is one of the country’s top functional medicine doctors and a member of the mbg Collective (if you didn’t catch his panel on mitochondria at 2017’s revitalize, it’s a can’t-miss!).  In his just-released book, Food: What the Heck Should I Eat?, he takes the complicated world of healthy eating and makes it simple and, well, easy to digest. Hyman analyzes all of the latest science to cut through the confusion and tell you exactly what’s good for your body, and, in a very You. We. All.-friendly way, for the planet at large. Ultimately, he concludes that the healthiest way to eat is a play on paleo and vegan: the pegan diet. In this excerpt, he explains exactly what that means.

The choice of nutritional philosophies is endless these days: We can go vegan; vegetarian; ketogenic; Paleo; flexitarian; pescatarian; Mediterranean; high-fat, low-carb; high-carb, low-fat; raw; and on and on. Trying to find the best one can be overwhelming. I’ve spent many years studying nutrition, and even I have trouble sometimes sifting through all the conflicting science and opinions. For years I tried different diets. I was a vegetarian. Then I went paleo. But eventually, I got fed up. It seems like the world of nutrition is being divided into armed camps, each proclaiming its superiority and decrying the fatal flaws in all the others. The obvious fact is that they all have advantages and disadvantages.

The vegan diet, for example, ideally incorporates plenty of whole, plant-based foods. As a result, vegans get lots of vitamins, minerals, antioxidants, fiber, and healthy fats with none of the baggage that comes with feedlot meat. They’re also making the world a more humane place for the creatures that are treated cruelly by industrial farms, along with reducing their carbon footprint. But even a perfect vegan diet won’t provide enough DHA and EPA, which are important omega-3 fatty acids. Neither will it provide enough iron, zinc, copper, or vitamin D. Vegans are also unlikely to be getting the amount of quality proteins and essential amino acids they require, especially as they age. It’s possible to find sufficient amounts in non-animal sources, but it is incredibly challenging. But they’re definitely not getting B12 because it only comes from animal foods. Finally, it’s entirely possible to be a vegan and still eat a poor diet filled with sugar, refined grains and flour, highly processed oils, soy-based protein substitutes, and foods loaded with chemicals and additives. You can live on Oreos, potato chips, and root beer and still call yourself a strict vegan. Even if you were to swear off wheat and gluten, a common staple in many vegan diets, the food industry is booming with “gluten-free” food items that trick us with misleading health claims on the label. Just because the gluten has been removed from something doesn’t mean it’s healthy; often, it means the exact opposite. If you eat a gluten-free brownie full of gluten-free refined flours and tons of sugar, you’re still wreaking havoc on your blood sugar and weight.

In the last six years, the paleo diet has become the most popular diet among health and wellness advocates. As we all know by now, this regimen is based on the idea that our bodies do best when fueled by foods that existed during the Paleolithic era, before agriculture came along 10,000 or so years ago. That means no sugars (except maybe honey and those occurring naturally in fruit), no grains, no dairy, no legumes or beans, and only nonindustrial meat, fish, whole nonstarchy vegetables, some starchy root vegetables and winter squashes, fruit (but not too much), nuts, and seeds. And that’s about it. As extreme as that may sound, it can be a healthy, low- glycemic diet, especially at a time when so many people are in ill health from eating grain-based sugary foods made with overly processed fats and oils. In fact, emerging research is using this approach, and a more aggressive approach called a ketogenic diet (very-low-carbohydrate, high-fat diet), to reverse type 2 diabetes.

However, some use the paleo philosophy as an excuse to eat too much meat and too few plant-based foods. As critics point out, there were many diets in the paleo era, depending on what part of the world we’re talking about. Back then, humans foraged for their food, mostly plants, and ate animals only when they could find, catch, and kill them. Meat wasn’t nearly as abundant as it is now. Meanwhile, our prehistoric ancestors had a huge amount of healthy plant fiber in their diets (100 to 150 grams a day vs. 8 to 15 grams a day, which is the modern average). Our healthy plant fiber intake doesn’t come anywhere close. I’ve tried both of these diets (vegan and paleo) and plenty of others, but I always wind up finding my way back to a happy medium. A few years ago I was on a panel with two other doctors; one was a paleo advocate and the other a strict vegan cardiologist. I was sitting in the middle, and to lighten things up I joked, “Well, if you’re paleo and you’re vegan, then I must be a pegan.”

All joking aside, the best versions of both diets are built on the same foundation: Eat real, whole food. Vegan and paleo diets focus on foods that don’t raise our blood sugar, plenty of fresh vegetables and fruits, healthy protein and fats, and no crap. I synthesized the best aspects of each and integrated them with the anti-inflammatory and detoxification principles of functional medicine to create a balanced, inclusive dietary plan that changed my life and my patients’ lives, too. Now thousands of people all over the world are following the pegan diet.

This is not a quick fix that you follow for 10 or 30 days and then quit. After you reset your body, I recommend eating this way every single day. It is inclusive, not exclusive, and based on sound nutritional science and working with patients for more than 30 years.

That means a diet low in anything that causes a spike in our insulin production—sugar, flour, and refined carbohydrates. Think of sugar in all its various forms as an occasional treat, that is, something we eat occasionally and sparingly. I tell people to think of it as a recreational drug. You use it for fun occasionally, but it is not a dietary staple.

As we learned earlier, more than half your plate should be covered with veggies. The deeper the color, the better. The more variety, the healthier. Stick with mostly nonstarchy veggies. Winter squashes and sweet potatoes are fine in moderation (½ cup a day). Not a ton of potatoes! French fries don’t count even though they are the No. 1 vegetable in America.

This is where there could be a little bit of confusion. Some paleo champions recommend eating mostly low-sugar fruits like berries, while some vegan advocates recommend all fruit equally. I find that most of my patients feel better when they stick to low-glycemic fruits and enjoy the others as a treat. Stick with berries, and watch the grapes, melons, and so on. Think of dried fruit as candy, and keep it to a minimum.

Also, no chemicals, additives, preservatives, dyes, artificial sweeteners, or other junk ingredients. If you don’t have that ingredient in your kitchen for cooking, you shouldn’t eat it. Polysorbate 60, red dye 40, and sodium stearoyl lactylate (also known as Twinkie ingredients), anyone?

I’m talking about omega-3 fatty acids and other good fats like those we find in nuts, seeds, olive oil, and avocados. And yes, we can even eat saturated fat from fish, whole eggs, and grass-fed or sustainably raised meat, grass-fed butter or ghee, and organic virgin coconut oil or coconut butter.

This includes canola, sunflower, corn, grapeseed, and especially soybean oil, which now accounts for about 10 percent of our calories. Small amounts of expeller or cold-pressed nut and seed oils like sesame, macadamia, and walnut oils are fine to use as condiments or for flavoring. Avocado oil is great for higher-temperature cooking.

As we learned in earlier chapters, dairy doesn’t work for most people, so I recommend avoiding it, except for the occasional yogurt, kefir, grass-fed butter, ghee, and even cheese if it doesn’t cause any problems for you. Try goat or sheep products instead of cow dairy. And always go organic and grass-fed.

Vegetables should take center stage, and meat should be the side dish. Servings should be 4 to 6 ounces, tops, per meal. I often make three or four vegetable side dishes.

If you are eating fish, you should choose low-mercury and low-toxin varieties such as sardines, herring, anchovies, and wild-caught salmon (all of which have high omega-3 and low mercury levels). And they should be sustainably harvested or farmed. Check out www.cleanfish.com and www.foodthebook.com to learn more about your fish options.

Most gluten comes from Frankenwheat, so look for heirloom varieties of wheat like einkorn. Eat wheat only if you are not gluten-sensitive, and even then, only occasionally. Dr. Alessio Fasano of Harvard, the world’s top gluten expert, has done research showing that gluten damages the gut—even in non-gluten-sensitive people who show no symptoms.

They still raise blood sugar and can trigger autoimmunity. All grains can increase your blood sugar. Stick with small portions (½ cup per meal) of low-glycemic grains like black rice, quinoa, teff, buckwheat, or amaranth. For type 2 diabetics and those with autoimmune disease or digestive disorders, a grain- and bean-free diet may be key to treating and even reversing your illness.

Lentils are best. Stay away from big starchy beans. Beans can be a great source of fiber, protein, and minerals. But they cause digestive problems for some, and the lectins and phytates they contain may impair mineral absorption. If you are diabetic, a high-bean diet can trigger spikes in your blood sugar. Again, moderate amounts (up to 1 cup a day) are OK.

What works for one person may not work for another. This is called bio-individuality, and it is why I recommend that everyone eventually work with a functionally trained nutritionist to personalize their diet even further with the right tests.