The bestselling author of The Plant Paradox returns to explain the science behind longevity—a field full of misunderstandings among laypersons and health professionals alike.

In an earlier book (The Plant Paradox), we went back 450 million years and saw how plants—just like animals—develop defensive strategies to ensure the survival and reproduction of its kind, like developing seeds and skins and other toxic proteins that trigger inflammatory reactions in the animals that eat them.

But let’s go back even farther this time—3 billion years, when bacteria ruled the earth. They inhabited a planet that would be hostile to most life forms on the planet today. They lived and reproduced anaerobically (i.e., without oxygen). In fact, oxygen was toxic for them.

These prokaryotic organisms made a deal with unicellular organisms in order to increase the chances of survival and dissemination of genetic material for both parties. This symbiotic relationship entailed a stable home in exchange for energy supplies. This paved the way for the emergence of multicellular organisms, from fungi and fish to plants and birds and human beings. It’s a strange thought, but bacteria essentially created animals.

The bacteria housed in other unicellular organisms are what we now call mitochondria—the powerhouse of the cells. They take all the oxygen you inhale and the food you ingest to create energy for your cells. Eventually, bacteria were not only housed in cells, but within the digestive tracts of larger animals. In both cases, bacteria were able to find refuge from the toxic oxygen-rich environments that came with the emergence of oxygen-producers like algae and plants.

Both the mighty mitochondria and the bacteria that migrated to the gut of animals served vital purposes. This then is the Longevity Paradox: your well-being and lifespan are in the hands of trillions of microbes that you unknowingly house. You are like the landlord of a condominium inhabited by trillions of tiny creatures. They help maintain good plumbing, security, and fresh outer paint. If you introduce junk into your system, you leave the condo open to microscopic squatters, and criminals hijack operations and ruin the condo.

Did you know that corn and fleas have more complex genomes than humans do? The water flea has 31,000 genes—the most of any animal. Corn has 32,000. Humans have only 20,000. This surprises a lot of people. “But we’re so much more complex!” Complex we are, but to what do we owe our complexity? We naturally assume that genetics best explains our complexity, but it’s bacteria that makes us complex, and, really, makes humans human. In fact, 90 percent of “your” cells aren’t really your cells at all, but an assortment of bacteria, worms, fungi, and other protozoa. Creepy?

People are uncomfortable with the thought that so much of our person is subject to the whims of trillions of bacteria in the gut, mouth, and skin, but you’re their host, whether you like it or not, and they are far more influential than your genetics. So 23andMe and your family tree are inferior predictors of your fate than the state of your gut buddies.

Taking care of your gut flora is a challenge for anyone who sticks to a Western diet and lifestyle. If that’s you, it’s likely that your gut is crawling with invading microbes who are happy to enjoy a parasitic existence rather than a symbiotic relationship like you would have with your gut buddies. The consequences of following the Western diet are becoming increasingly clear. Between 1960 and 2013, average lifespan increased by about a decade for both men and women, but over the past three years, those numbers are declining. Not only is lifespan decreasing, but healthspan is as well. We might live longer than our ancestors, but the quality of life deteriorates dramatically around 50. The new normal of old age includes an impressive prescription medication regimen, joint replacements or other surgeries, and chronic aches and pains. The elderly move their bedrooms to the ground floor in anticipation of trouble scaling stairs when groups like the Sardinians of the western Mediterranean often live to 100 and scale mountains right until the end.

We are not complex because of our genetic makeup. We are complex because of the bacteria that now inhabit us. Family trees and your parents’ medical histories don’t predict your longevity and health nearly as well as the state of your bacteria. It is thus imperative to know both how we can help them and the ways we unwittingly harm them.

There are a number of myths about longevity that need to die, but many so-called health professionals perpetuate them. One myth is the Mediterranean Diet. There are several locations around the world, sometimes referred to as the “Blue Zones,” where populations reach 100 years of age 10 times more frequently than in the United States. This has led some nutritionists and health experts to conclude that it must be what these groups are eating that’s giving them such long life. It’s true that there are several pockets across the planet where people live longer than others, and some of them are in the Mediterranean, but the prescribed Mediterranean Diet is built on half-baked conclusions and flat-out myths.

The problem with praise for the Mediterranean Diet is that the lengthened life span has far more to do with what people are not eating than what they are eating. People live longer not because of but in spite of some of the things they eat. One component that is harmful is gluten. Gluten is one of hundreds of plant proteins that wreaks havoc on our gut, triggers an inflammatory response, and arrests our gut’s efforts to absorb nutrients and fight invaders. Moreover, some Blue Zone groups have other chronic illnesses. There are high rates of chronic arthritis among the Italians because cereals feature so prominently in their diets. The Sardinians (from an island in the Western Mediterranean) tend to live longer as well, but many struggle with autoimmune diseases.

What the world’s diverse Blue Zone diets do have in common is lots of vegetables and negligible amounts of meat. The Okinawans of Japan have a plant-based diet and eat pork only occasionally. In Ikaria, Greece, families will slaughter a pig every year, but ration it over the course of several months. Maybe we should rethink the notion that meat protein is essential to health and aging. In 2018, the average American consumed 22 pounds of red meat and chicken, and yet the United States is far from being a Blue Zone. The benefits of meat are part of yet another myth that is killing us and itself refuses to die.

Among the other myths that trip us up are:

-That the wildly popular paleo and keto diets work.

-That a fast metabolism is a strong indicator of good health.

-That more iron in the blood increases lifespan (quite the opposite, actually. Women lose iron every month, which is why they tend to live longer).

If you want a longer lifespan and healthspan, the most important changes you can make are dietary. The following foods are terrific for you, and your gut bacteria love them. This list is not exhaustive, but these are some of their favorites. All of these items are terrific prebiotics—not to be confused with probiotics. Probiotics are the gut buddies themselves, and prebiotics are the food sources that your gut buddies feast on. Your good bacteria are always happy to munch on fibrous long-chain sugars. Just as it’s not enough to have grass seed without water and fertilizer, it’s no good having probiotics without prebiotics.

Most roots, tubers, and fungi are great for you, and packed with prebiotics. Ground flaxseed is a super additive. It’s been around and part of the human diet for at least 5,000 years, so our gut flora are well adapted to it. Other gut-promoting super foods are artichokes, leeks, okra, mushrooms, cruciferous vegetables like broccoli, cauliflower, and Brussel sprouts. Few veggies deliver more benefit than Brussel sprouts. Full of B, C, and K vitamins, they also have antioxidant and anti-inflammatory qualities.

Nuts are also excellent prebiotic sources, and support gut bacteria that produce butyrate, a fatty acid that optimizes mitochondrial function and has been shown to have anti-obesity and anti-diabetic properties. Butyrate also hampers the proliferation of cancer cells and improves learning capabilities among Alzheimer’s patients. A Yale study found that when stage 3 colon cancer patients ate just two servings of nuts per week, the recurrence of cancer dropped by 42 percent, and the rate of death decreased by 57 percent. This small adjustment made an enormous difference. To be clear, some nuts are more beneficial than others. Tree nuts are generally the best. Walnuts, pistachios, macadamia nuts, chestnuts , and hazelnuts are wonder foods. Cashews and peanuts, not so much. Cashews (which are actually seeds) contain lectins, and even worse are peanuts (which are actually legumes).

Coconut meat, figs, avocados, and green bananas are sweet but healthy options. Of cooking oils, coconut and olive oil are among the best. Ghee (clarified butter) is also a great option and a healthy butter substitute.

Your morning cup of Joe is also a good habit to hang onto. Green tea is another excellent option, as is a glass of red wine. An ounce of extra-dark chocolate is an indulgent, guilt-free treat that also strengthens your gut microbiome.

Even more important than eating foods that create an environment in which your gut bacteria can flourish is getting rid of the foods that harm them and leave an open door to invaders. The following are foods that will harm your gut flora and wreak havoc on your body. Here are some of the worst of the worse.

Glucose, fructose, and sucrose have to go. Fructose is the compound that makes fruit sweet, but it is also what makes fruit toxic. If you think you like fruit, the bad bugs that have hijacked your body’s systems like it more. Grapes, mangoes, ripe bananas, lychees, apples, pineapple, and pears are doing you more harm than good. There are about 6 teaspoons of sugar in just one cup of grapes. One mango has about 12 teaspoons of sugar. Splenda and other artificial sweeteners also harm your microbiome. One Duke study found that a single packet of Splenda wipes out half of your gut flora.

Dairy should also be avoided because a outside of southern Europe, cow’s milk contains casein-A1 proteins, which trigger autoimmune attacks. More people are lactose-intolerant than we think—it’s a question of severity. No one drinks milk without an ensuing mucus build-up.  What people forget is that mucus is one of the body’s most basic immune responses to the presence of a threat—which is exactly what the casein-A1 protein in milk triggers every time you drink it.

As far as oils, avoid peanut oil at all costs. It’s horrible for heart health and leads to inflammation that leaves the body vulnerable to bad bugs. The same is true of grape seed oil, corn oil, sunflower oil, canola oil, and partially hydrogenated vegetable oil.

In addition to foods, there are more general lifestyle choices that will support your gut buddies. Going outside and moving your body is key. It’s a way to beat stress (which, at high levels, can be poisonous for your body), and your gut buddies return the favor by fixing up the condo.

Make sure you get lots of Vitamin D3. Four in every five people who come to see the author are Vitamin D-deficient. 100 percent of his lectin-intolerant and autoimmune patients are Vitamin D-deficient. Vitamin D3 increases the absorption of nutrients in the gut. Studies have found that when severely malnourished children were given high daily doses of Vitamin D3, every single one gained weight quickly--even though there was no change in the calories consumed!

Make sleep a priority. Eight hours of solid slumber is not a luxury but a necessity. Your brain, body, and friendly bacteria depend on it. Make your sleep-wake patterns more consistent. Invest in bluelight-blocking glasses that can remove excessive blue spectrum light that tablets, smart phones, computers, and TVs emit. Bluelight tells the body it’s summer and makes you crave fruits and sweets. It also tells the body that it’s day time, which is why excessive use of screens, especially at night, can disrupt your sleep hormone cycles. When it’s dark outside, the body begins to produce sleep-inducing melatonin. So when you are taking in bluelight from your television or phone late at night, your body gets mixed messages: it wants to produce melatonin, but it interprets the bluelight as daylight, and so it produces hormones that promote wakefulness, too. It’s a mess.

One final thing to consider is that just about every centenarian with whom the author has interacted has a particular attitude toward life, which he calls a “pessimistic optimism.” They shrug their shoulders about the hard things and the things they can’t change, and celebrate the numerous good things that still remain. A healthy lifestyle and good nutrition coupled with a supportive community and attitude of pessimistic optimism will do wonders for your health. Old age will no longer be something to dread but to be embraced.