Dr. Catherine Shanahan begins her updated and expanded edition of Deep Nutrition: Why Your Genes Need Traditional Food with a dedication to a few of her former patients – members of a certain family who all experienced health problems, and one of whom died from their condition. The author recalls that they didn’t eat well, and she regrets not having the chance to intervene sooner with dietary education, which she calls “the most powerful form of preventive medicine.”

Patients like these motivated Dr. Shanahan to update Deep Nutrition. She wrote the first edition in 2009 to educate people about the importance of a healthful diet based on traditional food, and she felt the need to renew it after realizing that many people still don’t understand how poor nutrition affects them as well as their offspring. The first edition changed the conversation; however, she writes, it didn’t do enough.

Dr. Shanahan’s message is thus: A diet based on four fundamental food categories – “the four pillars of the human diet” (meat on the bone, sprouted and fermented foods, organs and other ‘nasty bits’, and fresh, unadulterated plant and animal products) – will improve not only your present and future well-being, but that of your descendants, as well.

The author, a board-certified family physician, lays out a comprehensive argument for avoiding foods that are standard components of the American diet (dedicating a few chapters to the dangers of vegetable oils and sugar); she writes in such a way that the science behind her recommendations doesn’t feel like a lesson, but more like a chat with an old friend. The book is updated with new scientific findings, additional and expanded chapters, and a large Frequently-Asked-Question section, all at the recommendations of readers.

The first few chapters explore genes and epigenetics (changes in gene expression), and the role of nutrition in both realms. The way we take care of ourselves exerts a “ripple” effect upon later generations; for instance, if a person’s diet lacks calcium and vitamin D and they eventually develop osteoporosis, their familial gene for bone growth may “take a nap”, she writes. If a woman smokes during pregnancy, her grandchildren may have a higher risk of developing asthma, even if their mother herself never smoked. Even attractiveness, which is closely linked to facial and bodily symmetry, seems to be reliant on the proper nutrition of those who came before us. It’s an outward expression of good genes.

“Getting sick isn’t random,” Dr. Shanahan writes. “We get sick because we’ve failed to provide our genes with what they were expecting, one too many times. Most importantly, I’ve learned that food can tame unruly genetic behavior far more reliably than biotechnology. By simply replenishing your body with the nourishment that facilitates optimal gene expression, it’s possible to eliminate genetic malfunction, and with it, pretty much all known disease.”

Dr. Shanahan and her co-author and husband, Luke Shanahan, do an excellent job of explaining why we should focus on those four “pillar foods,” and how our bodies are programmed to live optimally on them, since they’re “the components that every successful traditional diet has in common.”

“These fundamental foods provide healthy people all around the world with the consistent stream of nutrition that, no matter the regional culinary peculiarities, thoroughly furnishes the nutritional inputs our bodies have been programmed to require,” Dr. Shanahan writes. “Though each local interpretation appears unique, as far as your body’s cells are concerned, healthy diets are all essentially the same.”

The authors offer clear, concise recommendations for best applying the “four pillars” to your diet, such as why to purchase organic, pasture-raised meat, why you should eat animal fat, and why you should cook your meat slowly (it brings out not only more flavor, but more nutrients, too). They also give useful guidelines for sourcing and eating a “human diet” in the modern food landscape. Chapter 13 presents Dr. Shanahan’s “clinic-tested approach” to switching to a healthy way of eating, listing foods relevant to each pillar, helping the reader understand macronutrient ratios, and even providing meal plans and shopping lists.

Deep Nutrition is a thoroughly enjoyable and fascinating read, and easily deconstructs the science behind its arguments. By doing so, it may make you pass up that chocolate bar or bag of chips next time they’re within reach – after all, they’re not just harming you calorically in the short term, but also affecting the health of your children and future self.

“Whatever your age, whatever illnesses run in your family, whatever your ‘risk factors’, however many times you’ve tried to lose weight or build muscle, eating the foods I’ve described will transform your body. And if you are planning to conceive, eating Four-Pillar foods before, during and after conception (and of course feeding them to your child as he or she grows) will allow the genes in his or her body to express in ways that yours may not have.”