A Publishers Weekly Best Book of the Year
From an obesity and neuroscience researcher with a knack for engaging, humorous storytelling, The Hungry Brain uses cutting-edge science to answer the questions: why do we overeat, and what can we do about it?
No one wants to overeat. And certainly no one wants to overeat for years, become overweight, and end up with a high risk of diabetes or heart diseaseyet two thirds of Americans do precisely that. Even though we know better, we often eat too much. Why does our behavior betray our own intentions to be lean and healthy? The problem, argues obesity and neuroscience researcher Stephan J. Guyenet, is not necessarily a lack of willpower or an incorrect understanding of what to eat. Rather, our appetites and food choices are led astray by ancient, instinctive brain circuits that play by the rules of a survival game that no longer exists. And these circuits don’t care about how you look in a bathing suit next summer.
To make the case, The Hungry Brain takes readers on an eye-opening journey through cutting-edge neuroscience that has never before been available to a general audience. The Hungry Brain delivers profound insights into why the brain undermines our weight goals and transforms these insights into practical guidelines for eating well and staying slim. Along the way, it explores how the human brain works, revealing how this mysterious organ makes us who we are.
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About the Author
Stephan J. Guyenet, Ph.D. is an obesity researcher and health writer whose work ties together neuroscience, physiology, evolutionary biology, and nutrition to offer explanations and solutions for our global weight problem. He received a B.S. in biochemistry at the University of Virginia and a Ph.D. in neurobiology at the University of Washington. He is the author of the popular health website, Whole Health Source, and is a frequent speaker on topics of obesity, metabolism, and nutrition.
Read an Excerpt
The Hungry Brain
Outsmarting the Instincts That Make Us Overeat
By Stephan Guyenet
Flatiron BooksCopyright © 2017 Stephan Guyenet
All rights reserved.
THE FATTEST MAN ON THE ISLAND
Stout but not quite obese, and boasting a prominent belly, Yutala would have been an unremarkable-looking man in many places. He would not have stood out on the streets of New York, Paris, or Nairobi. Yet on his native island of Kitava, off the coast of New Guinea, Yutala was quite unusual. He was the fattest man on the island.
In 1990, researcher Staffan Lindeberg traveled to the far-flung island to study the diet and health of a culture scarcely touched by industrialization. Rather than buying food in grocery stores or restaurants like we do, Kitavans used little more than digging sticks to tend productive gardens of yams, sweet potatoes, taro, and cassava. Seafood, coconuts, fruits, and leafy vegetables completed their diet. They moved their bodies daily and rose with the sun. And they did not suffer from detectable levels of obesity, diabetes, heart attacks, or stroke — even in old age.
As extraordinary as this may sound to a person living in a modern society beset by obesity and chronic disease, it's actually typical of nonindustrialized societies living similarly to how our distant ancestors might have lived. These societies have their own health problems, such as infectious disease and accidents, but they appear remarkably resistant to the disorders that kill us and sap our vigor in affluent nations.
As it turns out, Yutala wasn't living on Kitava at the time of Lindeberg's study; he was only visiting. He had left the island fifteen years earlier to become a businessman in Alotau, a small city on the eastern tip of Papua New Guinea. When Lindeberg examined him, Yutala was nearly fifty pounds heavier than the average Kitavan man of his height and twelve pounds heavier than the next heaviest man. He was also extraordinary in another respect: He had the highest blood pressure of any Kitavan examined by Lindeberg. Living in a modern environment had caused Yutala to develop a modern body.
Yutala is a harbinger of the health impacts of industrialization. His departure from a traditional diet and lifestyle, and subsequent weight gain, form a scenario that has played out in countless cultures around the globe — including our own culture, our own families, and our own friends. In the United States, we have a tremendous amount of information about the diet, lifestyle, and weight changes that accompanied this cultural transition. This will provide us with valuable clues as we piece together the reasons why our brains drive us to overeat, despite our best intentions. Let's start by examining how our weight has changed over the last century.
THE COST OF PROGRESS
In New Guinea, as in many other places around the globe, industrialization has triggered an explosion of obesity and chronic disease. If we look back far enough, we can see traces of the same process happening in the United States.
In 1890, the United States was a fundamentally different place from what it is today. Farmers made up 43 percent of the workforce, and more than 70 percent of jobs involved manual labor. Refrigerators, supermarkets, gas and electric stoves, washing machines, escalators, and televisions didn't exist, and motor vehicle ownership was reserved for engineers and wealthy eccentrics. Obtaining and preparing food demanded effort, and life itself was exercise.
How common was obesity among our American forebears? To find out, researchers Lorens Helmchen and Max Henderson pored through the medical records of more than twelve thousand middle-aged white Civil War veterans and used their height and weight measurements to calculate a figure called the body mass index (BMI). BMI is basically a measure of weight that is corrected for height so we can compare weights between people of different statures. It's a simple measure that's commonly used to classify people as lean, overweight, or obese (a BMI below 25 is classified as lean; 25 to 29.9 is overweight, and 30 and above is obese). When Helmchen and Henderson crunched the numbers, they found something truly remarkable: Prior to the turn of the twentieth century, fewer than one out of seventeen middle-aged white men was obese.
The researchers then calculated the prevalence of obesity in the same demographic between 1999 and 2000 using data from the US Centers for Disease Control and Prevention. They found that it started at 24 percent in early middle age and increased sharply to 41 percent by retirement age. Side-by-side comparison of the data from 1890 to 1900 and 1999 to 2000 yields a striking contrast (see figure 1).
This suggests that obesity was much less common in the United States before the turn of the twentieth century, just as it remains uncommon in traditionally living societies today. Although obesity has existed among the wealthy for thousands of years — as demonstrated by the portly 3,500-year-old mummy of the Egyptian queen Hatshepsut — in all of human history, it has probably never been as common as it is today.
Let's take a closer look at the last half century, because that's the period over which our data are the most reliable — and during which these numbers have changed most dramatically. In 1960, one out of seven US adults had obesity. By 2010, that number had increased to one out of three (see figure 2). The prevalence of extreme obesity increased even more remarkably over that time period, from one out of 111 to one out of 17. Ominously, the prevalence of obesity in children also increased nearly fivefold. Most of these changes occurred after 1978 and happened with dizzying speed.
Public health authorities call this the "obesity epidemic," and it's having a profound impact on health and well-being in the United States and throughout the affluent world. The latest research suggests that we may be gravely underestimating the health impacts of obesity, as up to one-third of all deaths among older US adults is linked to excess weight. Diabetes rates are soaring, as are orthopedic problems caused by obesity. Nearly two hundred thousand Americans per year are having their digestive tracts surgically restricted or rerouted to lose weight. Clothing is now available in staggering sizes such as XXXXXXXXL.
Why are we so much fatter than we used to be? The answer lies in what we've been eating and how it relates to the fat we carry, which we'll explore shortly. But we first have to understand how food delivers energy to our bodies.
THE CALORIE IS BORN
Contrary to popular belief, the term calorie was not invented by SnackWell's. Rather, it was coined in the early 1800s and was used by scientists to measure energy in all its different forms by the same metric: as heat, light, motion, or the potential energy contained in chemical bonds. These chemical bonds are found in bread, meat, beer, and most other foods, which release their potential energy as heat and light when burned, just like wood or gasoline.
In 1887, Wilbur Atwater, the father of modern nutrition science, described how the potential energy in food fuels the furnace of the human body:
The same energy from the sun is stored in the protein and fats and carbohydrates of food, and the physiologists to-day are telling us how it is transmuted into the heat that warms our bodies and into strength for our work and thought.
Recognizing the power of energy as a way to understand our bodies, Atwater's team was the first to exhaustively measure the calorie content of different foods by burning them in his energy-measuring "calorimeters." When you see a calorie value on the side of your box of cereal, it was calculated using formulas Atwater developed by measuring the calorie content of food and adjusting it for the intricacies of human digestion and metabolism. (The values are actually in kilocalories, or thousands of calories, which is denoted by capitalizing the word Calorie, a convention begun by Atwater.)
Atwater and his colleagues also constructed a giant live-in calorimeter to measure the combustion of food by the human body. This calorimeter was large enough to provide a modest living space for experiments lasting multiple days. Atwater's system was so effective that it was able to demonstrate with greater than 99 percent accuracy that the energy entering a weight-stable person as food is equal to the energy leaving the body. In other words, in a person neither gaining nor losing weight, the number of calories consumed is equal to the number burned.
This statement can be rearranged as the energy balance equation:
Change in body energy = energy in - energy out
Energy enters the body as food, and it leaves as heat after we've used it to do metabolic housekeeping, pump blood and breathe, digest food, and move our bodies. We also use it to build lean tissues, such as muscle and bone, during growth. Any energy that's left over after the body has used what it needs is stored as body fat, technically called adipose tissue. Adipose tissue is the major energy storage site of the body, and it has an almost unlimited capacity. When you eat more calories than you burn, the excess calories are primarily shunted into your adipose tissue. Your adiposity, or body fatness, increases. It really is as simple as that, although as we'll see in later chapters, the implications are not as straightforward as they initially appear.
Atwater also discovered that chemical energy from different types of foods, including those rich in carbohydrate, fat, protein, and alcohol, is effectively interchangeable in the body: Roughly speaking, all calories are the same as far as the human furnace is concerned. More recent research has also supported the idea that the fat, carbohydrate, and protein content of foods has little influence on adiposity beyond the calories they supply. We know this because when researchers strictly control total calorie intake, varying the fat, carbohydrate, and protein content of the diet has no appreciable impact on adiposity — whether in the context of weight loss, weight maintenance, or weight gain. This undermines the commonly held belief that certain nutrients, like carbohydrate or fat, are more fattening than what their calorie content would suggest. Some foods are nevertheless more fattening than others, but this appears to be primarily because they coax us to eat more calories, not because they have a special effect on our metabolic rate.
With this in mind, we can adapt the energy balance equation to describe long-term changes in adiposity:
Change in adiposity = food calories in - calories out
To gain fat, you must eat more calories, burn fewer calories, or both. To lose fat, you must eat fewer calories, burn more calories, or both. It's a simple concept, although applying it to weight loss can be surprisingly difficult, as many people know all too well.
If this principle is true, then we should expect to see that Americans began eating more calories, and/or burning fewer calories, as our waistlines expanded. Let's have a look.
CALORIES IN: HOW OUR CALORIE INTAKE HAS CHANGED
Measuring calorie intake in an entire country is a challenging task. Yet researchers have so far managed to do it in three different ways. The first way is to measure food production, adjust for the amount that's being exported and imported, try to account for loss due to food waste, and see how many calories are left per person. The second way is simply to ask a representative sample of people what they eat and tally up the calories. The third way is to mathematically model the relationship between body weight and calorie intake, and use that model to calculate the change in calorie intake that should be required to produce the observed increase in weight.
I've graphed calorie intake estimates from all three methods in figure 3. As you can see, the methods yield different estimates, but they all agree that our calorie intake has increased substantially over the period of time that we gained weight the most rapidly (218–367 additional Calories per day between 1978 and 2006). The third method, pioneered by National Institutes of Health researcher Kevin Hall and highlighted in black on the graph, probably comes the closest to capturing the true increase in daily calorie intake over the course of the obesity epidemic: 218 Calories. Remarkably, this increase is single-handedly sufficient to explain the obesity epidemic that developed over the same period of time, without having to invoke changes in physical activity or anything else.
Right about now, you might be putting on your skeptic hat. One pound of body fat contains about 3,500 Calories, so if we're really overeating by 218 Calories per day, shouldn't we be gaining a pound of fat every sixteen days — twenty-three pounds per year — and requiring a forklift to get around after a decade or two? Actually, despite the popularity of this type of back-of-the-envelope math among popular media sources, public health authorities, doctors, and even some researchers, that's not how adiposity works. Hall and his colleagues have shown that this way of estimating changes in adiposity is way off target — and the consequences of this error have important implications for how we think about weight gain and weight loss.
The primary problem with this way of thinking is that it doesn't acknowledge the fact that as your body size changes, your body's energy needs change too. To illustrate the principle, think of your adipose tissue as a bank account. If you start out with $10,000 in savings, an income of $1,000 a month, and expenditures of $1,000 a month, in a year, your account will still contain $10,000. Now, imagine you get a raise and your earnings climb to $2,000 a month. At first, your lifestyle remains the same and you only spend $1,000 a month, saving the extra $1,000 per month. But gradually, you start to think it would be nice to have that new computer or fancy pair of shoes. You move into a nicer apartment. Your lifestyle expands, and your expenditures creep up. Six months after your raise, you're spending $1,500 per month, and after a year, you're spending the full $2,000 a month. Over this year, your bank account has been accumulating money, but at a gradually slowing rate, until accumulation stops when your expenditures match your income. Your account balance plateaus at about $16,000, and it remains there until your income or expenditures change.
And so it is for adiposity. When your calorie intake increases, your body weight increases, and this extra tissue burns calories. Gradually, as your body enlarges, your calorie expenditure comes to match your extra calorie intake, and you reach a weight plateau. You're no longer eating more calories than you're burning, so your weight and adiposity stabilize at a higher level. The same plateau effect happens in reverse when a person cuts her calorie intake.
What are the practical implications of this? An important one is that it takes a larger change in calorie intake to gain — or lose — weight than most people realize. Making small changes to your diet, such as cutting out one slice of toast per day, will lead to correspondingly small changes in adiposity that don't continue to accrue indefinitely. The new, evidence-based rule of thumb is that you must eat ten fewer Calories per day for every pound you want to lose. Yet it takes several years to arrive at a new stable weight, so most people will want to start with a larger calorie deficit to reach their target weight more quickly and then use the ten-Calorie rule of thumb to maintain the loss.
This offers a partial explanation for that scourge of conscientious dieters everywhere: the dreaded weight-loss plateau. This is where a person diligently cuts her calorie intake and successfully loses weight, but her weight loss stalls before she reaches her goal, even though she continues to follow her formerly successful diet. This phenomenon is real, and Hall's research offers two explanations for it. First, as a person loses weight, her smaller body needs less fuel, the calorie deficit gradually closes, and weight loss stalls. And second, weight loss ramps up her appetite, making it harder to maintain the calorie deficit (I'll explain why this happens in later chapters). To restart weight loss during a plateau, she must reestablish a calorie deficit, although that's easier said than done.
Excerpted from The Hungry Brain by Stephan Guyenet. Copyright © 2017 Stephan Guyenet. Excerpted by permission of Flatiron Books.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
1. The Fattest Man on the Island
2. The Selection Problem
3. The Chemistry of Seduction
4. The United States of Food Reward
5. The Economics of Eating
6. The Satiety Factor
7. The Hunger Neuron
9. Life in the Fast Lane
10. The Human Computer
11. Outsmarting the Hungry Brain