UPDATE: The new edition has launched! Books are in stock and shipping. Here is the Amazon page.

Readers of our first edition, like Steven, are naturally wondering what’s new in the Scribner edition.

There’s a lot that’s new. The Scribner edition is 50% longer; almost half of the material is new. Original material is revised and updated.

In a series of posts this week, I’m going to walk through the book and discuss what’s new and original. This post is about Part I, “An Evolutionary Guide to Healthful Eating.” (You can see a Table of Contents for the whole book on our Notes page, or in the Scribd excerpt below.)

Paleolithic Diets: An Evolutionary Story

Loren Cordain uses a striking analogy: he compares the length of the Paleolithic, 2.6 million years, to the length of a football field, 100 yards. By that scale, the Neolithic – the period when grains and farmed foods became a major part of our diet – is about a foot long. The point is that, in evolutionary terms, our relationship with agriculturally mass-produced cereal grains has been relatively short (to say nothing of our relationship with high-fructose corn syrup and soybean oil!). It stands to reason that we’d be adapted to the diet and lifestyle of the Paleolithic, and we agree, for reasons discussed in Chapter 1.

But what was the composition of Paleolithic diets? The Paleolithic was the era of stone tool use, and one of the primary purposes of stone tools was butchering animals, so the Paleolithic roughly corresponds to the period when meat was a significant part of our diet. But plants were also a major part.

The popular Paleo movement presents a fairly consistent view of what a “Paleo diet” is: meat and fish, fruits and vegetables, nuts and seeds. But how close is this “Paleo diet” to actual Paleolithic diets? Did Paleolithic peoples forgo starches? Did they eat almond meal waffles, muffins, and cookies? Looking into the actual Paleolithic diet is the subject of Chapter 2.

Unfortunately, the standard Paleo “evolutionary” argument doesn’t get us very far toward finding the optimal human diet. First, there was no one Paleolithic diet: it varied considerably by time and place. Second, the contention that our hunter-gatherer ancestors “adapted” to the diet they were eating and were optimized for it is open to question. Our biology is not infinitely malleable, capable of adapting to any diet. We could subsist on Twinkies for 2.6 million years, and Twinkies would never become the optimal human diet. How can we know that plants and animal foods gathered and hunted in the Paleolithic were then, or are now, our optimal diet?

Fortunately evolutionary evidence tells us much more about what is healthful for us, and what it tells us is supportive of the Paleolithic diet story.

A Richer Evolutionary Story

Evolution selects every aspect of our biology – how cells work, how organs work, how our brain works.

In the first edition, we gave a few very brief summaries of some alternative evolutionary arguments for the optimal human diet. We found that even very smart readers often misunderstood or didn’t appreciate the strength of these arguments, so we elaborated on them in the new edition.

These arguments are spelled out in Chapters 3-6: The “Cannibal Diet” of Fasting, What Breast Milk Teaches Us About Human Diets, What Mammalian Diets Teach Us About Human Diets, and The “Tastes Great!” Diet.

Why does fasting tell us about the optimal diet? Think about how food is handled. Our food doesn’t go straight from our digestive tract to our mitochondria to be turned immediately into energy. Instead, nutrients from food are incorporated into tissue within a few hours after a meal, and then that tissue is cannibalized to supply energy needs over the following 24 hours.

As a rule, tissues won’t accept just any macronutrients. Cells have a very specific structure, with fatty membranes and protein-rich cytosols; and they have very specific fatty acid profiles in their membranes, and amino acid ratios in their proteins. Cells specifically take up nutrients in the proportions they need, and refuse to incorporate nutrients they don’t need.

So if we evolved to be nourished by self-cannibalization of tissue, then the nutrient composition of our tissues must be close to our optimal diet.

What about breast milk? Most people will agree that this is the optimal food for infants. But many have thought there must be so many differences between infants and adults that breast milk will tell us little about the adult diet.

Not so. We can quantify the differences between infants and adults – they have mainly to do with the large and fast-growing infant brain – and can see which parts of the breast milk are designed to support that brain. We can adjust for those differences, and estimate the optimal adult diet from the composition of breast milk.

What about mammalian diets? I think this is one of the most interesting parts of our book and will be of great interest to pet owners, farmers, veterinarians, zookeepers, and anyone who has to feed animals.

The reality is that evolutionary selection has been operating for far longer than the Paleolithic, and it settled on certain solutions quite early. Multicellular life was common by 500 million years ago, and the basic composition of cells and their extracellular matrix scaffolding hasn’t changed much in that time.

So if our cellular biology hasn’t changed much in 500 million years, then the nutrients needed by cells hasn’t changed much either. That means the optimal diet hasn’t changed much. Yet there is a diversity of animals that occupies every possible ecological niche and type of food. How can a common biology be fed by a diversity of diets? Why are there herbivores, omnivores, and carnivores?

The resolution of this seeming paradox lies in the digestive tract and how it transforms food into nutrients. This allows us to infer from the digestive tract what an animal’s optimal diet is. We can do that for humans, too.

Those three evolutionary arguments were present in capsule form in the first edition, but the next one is entirely new to this edition: a discussion of the food reward system of the brain. Food reward evolved to motivate us to go seek out healthy, nourishing foods. If it evolved in the Paleolithic environment, then it tells us what foods were hard to get in the Paleolithic, but still necessary for health – these were the foods that Paleolithic foragers had to be motivated to work for.

But in our modern world, all foods are easy to obtain; they are on the shelves of supermarkets. So those foods that were hard to get in the Paleolithic are going to be precisely the ones that we overeat today.

The presence of an innate food reward system explains why peoples around the world eat very similar diets – almost always 50% carb, 15% protein, 35% fat, or close to it. If this food reward system evolved for the Paleolithic food environment, which was radically different from the modern agricultural and industrial global food production system, then we can’t trust our unconscious food buying impulses. If we just go to the supermarket and put whatever seems desirable into our cart, we will overeat all the things that our Paleolithic ancestors tended to undereat.

Worse, we will be tempted to eat junk foods designed to appeal to the tastes that signal healthfulness to the food reward system, without supplying the nutrients that actually deliver healthfulness.

On the other hand, this evolutionary argument is encouraging. It tells us that, if we eat Paleolithic foods and if we educate ourselves to select healthy foods in the optimal proportions, then we can be confident that our brains will find our meals to be delicious and satisfying.

A healthy diet is also a delicious and satisfying diet! There is no need to suffer to be healthy. There is no need to suffer to lose weight. If you are suffering on a diet, you are doing something wrong.

Part I ends by circling back to a recurring topic: animal diets. Our pets, zoo animals, and even feral rats living in urban areas and eating our trash are partaking of our ill health. They are becoming obese in parallel with us, and develop cardiovascular disease at similar rates; their wild counterparts do not have these problems. Yet returning zoo animals to their natural diets returns them to good health. Adopting our natural diet works for humans too. Our Perfect Health Diet reader success stories support this claim.

Evolutionary Fine-Turning

The rest of the book also puts some weight on evolutionary arguments. When we look at individual nutrients, we find that the body has evolved mechanisms to bring them close to an optimal level:

• The body adjusts toward an optimal carb intake. When carb intake is too high, glucose is converted to fat. When carb intake is too low, glucose is manufactured from protein. The Goldilocks level, at which the body neither manufactures nor disposes of glucose, is an indicator of the optimal carb intake.
• The body adjusts toward optimal fatty acid proportions. In Americans today, omega-6 fats are more than three times more likely to be burned for energy than saturated fats. Yet on omega-6 deficient diets, omega-6 fats are less likely to be burned for energy than saturated fats. This evolved system for regulating the body’s fatty acid composition is clear evidence that Americans eat too many omega-6 fats and too few saturated fats.

Similar arguments from evolutionary biology guide us toward optimal intake of micronutrients, which have degradation or excretion pathways turned on when they are present in excess, and conservation pathways turned on when they are scarce.

Cooperating with Our Bodies to Build Health

The earliest human temptation, if we are to believe the story of the Garden of Eden, was to “be as gods” and define good and evil — healthful and unhealthful — for ourselves. There is an undoubted attraction, we have felt it ourselves, to masterminding our diet and nutrition. We like to think that evolution got it wrong, or optimized for the wrong thing, and that an extreme diet or unnatural intervention can improve our health.

It’s not just extreme dieters who think this way. What is the pharmaceutical model of medicine, but the idea that we can alter the natural functioning of our bodies in ways that will make us healthier?

Sometimes this can work, but usually wisdom and deeper knowledge show us that evolution got it right, that our innate biology works to maintain our health rather than harm it, and that interventions which subvert natural functions tend to do more harm than good.

A more promising approach, we think, is to cooperate with our bodies. This leaves plenty of room for medicine to help – through diagnosis and testing, through antimicrobial treatments, through integrated dietary and lifestyle advice, and through interventions that support natural bodily functions (as, for instance, thyroid hormone replacement in hypothyroidism, or insulin therapy in type 1 diabetes).

It’s this cooperative approach, integrating the best of medicine with the best ancestral health practices, that we think will be most effective at generating good health and long life. We hope our book will illuminate what those “best ancestral health practices” are, and help build a cooperative effort between the natural health movement and the medical community.

Concluding Thoughts & a Book Excerpt

It could be said that our book is an “owner’s manual” for the human body, helping our readers know how to best support their own health by living in accord with our evolved biology.

The great thing is, the way to do this is by eating delicious, satisfying food!

If you’d like to get a feel for the book, check out this excerpt, which Scribner has put on Scribd:
PERFECT HEALTH DIET: How anyone can regain health and lose weight by optimizing nutrition, detoxifying the…