Eat, Drink, and Be Healthy

by Walter Willett

  THE OBESITY EPIDEMIC

  Carrying too many pounds is a very personal problem. It can shape how you feel about yourself and how others treat you. It has a direct effect on your current and future health. It costs you (or at least your health insurance company) tens of thousands of dollars more in medical costs over the years.1 And although excess weight is a personal problem, it is also a major public health problem.

  The first two decades of the twenty-first century could be called the obesity decades. Since the early 1960s the proportion of Americans who are moderately overweight has stayed the same, hovering around one-third.2 What has changed dramatically, though, is the number who are obese. More than one-third of American adults now fall into this category, almost triple the proportion from the early 1960s.3 Obesity among children has also increased dramatically over this period by three- to fourfold, an alarming trend given that early obesity leads to diabetes and cardiovascular disease at a young age. Although the percentage of children with obesity has leveled off in recent years, the number of children with it remains dangerously high. As a nation, we spend more than $200 billion a year4 on medical care for obesity and its complications.

  The situation isn’t much better elsewhere around the globe. The World Health Organization calls obesity a worldwide epidemic. And while deadly famines and starvation make headlines, overweight, obesity, and their health consequences have already replaced malnutrition and infection as the main causes of early death and disability in many developing countries.5

  WHAT IS A HEALTHY WEIGHT?

  What seems to be a simple question turns out to be remarkably difficult to answer. There are two parts of this problem. First, a weight that may be perfectly fine for someone who is six feet one—say 175 pounds—is way too much for someone who is five feet two. Another part is lingering confusion about the way healthy weight has been defined in the past.

  A number called the body mass index (BMI), or Quetelet index, gets around the first problem. This measure of weight adjusted for height does a good job of accounting for the fact that taller people tend to weigh more than shorter people. If you like math, you can calculate your BMI like this: Divide your weight in pounds by your height in inches; divide that number by your height in inches; and multiply that number by 703. You can also just look it up in the table on page 41 or have it calculated for you by any number of online BMI calculators, such as the one on the Harvard Health Publications website (www.health.harvard.edu/bmi).

  Setting guidelines for healthy BMIs has traditionally been done by examining death rates in large groups of people and then picking the BMIs with the lowest death rates as the “healthy range.” Most studies have shown that range to be BMIs between 18.5 and 24.9.

  Figure 8. BMI Tables. To use these tables, find your height in the left-hand column. Move across to a given weight. The number at the bottom of the column is your BMI.

  In 2013, several statisticians at the Centers for Disease Control and Prevention (CDC) published an analysis showing that the healthy range (meaning the lowest death rate) was among people who were overweight (BMIs between 25 and 29.9). In their analysis, overweight people were less likely to have died over the study periods than those who were at healthy weights (BMI between 18.5 and 24.9). As in other studies, individuals who were very thin or seriously obese were also more likely to have died. The report, published in the Journal of the American Medical Association,6 garnered widespread press coverage, spawning headlines like “How Love Handles Can Help You Stay Healthy,” “Astonishing New Research Shows How Being Overweight Can Stop You from Dying Early,” and “Carrying a Few Extra Pounds Could Protect the Heart.”

  These findings don’t make sense. How can being overweight, which increases the likelihood of developing type 2 diabetes, heart disease, many cancers, and other chronic conditions—all of which are known to reduce life expectancy—be better than healthy weight when it comes to survival?

  Although the CDC study was a large one, including more than 2.8 million people, it ignored key information that distorted the results. The problem with the study, and similar ones that came before it, is that they included smokers and people who were chronically ill but didn’t fully account for the effects of these.

  Cigarette smokers tend to be leaner than nonsmokers, in part because smoking blunts the appetite. People who smoke heavily are likely to be leaner than light smokers. Because smoking is such a powerful risk factor for death, this will tend to make being lean look unhealthy. Also, in any large population, the leanest people are a mix of a small number of thin people who have managed to strike a long-term balance between the number of calories they take in and the number they burn plus people who are thin because they have illnesses that are accompanied by weight loss (such as cancer, heart disease, emphysema, and frailty in the elderly). In other words, low weights don’t necessarily cause premature death but are instead often the result of diagnosed or undiagnosed illnesses that eventually will be fatal. These confounding factors make the leaner group appear to be more likely to die prematurely. By comparison, then, the overweight group will appear to be less likely to die prematurely.

  Two strategies can sidestep these limitations: (1) Look only at nonsmokers. (2) Ignore in the data crunching any deaths that occur during the first few years of follow-up to eliminate individuals with previously undiagnosed cancer or other conditions that would have accounted for their low weight.

  My colleagues and I did just that in a 2016 analysis that combined data from 239 cohort studies that included more than 10 million men and women between the ages of 35 and 89 from all around the world. During a follow-up period averaging fifteen years, we saw that the lowest death rates were among people with BMIs between 18.5 and 24.9, much as we had expected.7 Among those with BMIs above 25, the greater the weight, the greater was the risk of dying during the study period. The relation between weight and mortality was similar across all geographic regions of the world.

  Another 2016 meta-analysis that included more than 30 million people8 concluded the same thing.

  CURRENT WEIGHT GUIDELINES CAN BE TOO GENEROUS

  The 2015–2020 Dietary Guidelines for Americans sets healthy weights as those corresponding to BMIs between 18.5 and 25. BMIs above 25 are labeled as unhealthy (see Figure 9). In choosing these limits, the Scientific Advisory Committee for the 2015–2010 Dietary Guidelines for Americans tried to balance scientific evidence with public policy and perception. That’s a difficult job, because there is no simple break point between healthy and unhealthy weights. Panel members agreed that the risk of heart disease, diabetes, and high blood pressure begins to climb at a BMI of 22 or so. But they didn’t feel justified choosing such a low number as the cutoff between healthy and unhealthy weights, because doing so would have labeled a large majority of the U.S. population as overweight. Instead they chose a BMI of 25 as the upper bound of healthy weights, based on clear evidence that the risk of dying prematurely increases above that point. (The guidelines committee didn’t include the 2013 CDC study I described earlier [see page 42]). That means almost everyone with a BMI over 25—except for extremely muscular bodybuilders—would be healthier with a lower BMI, but many people with a BMI of 23 to 25 are not at their healthiest weight. Still, drawing the line at 25 means that two-thirds of adult Americans are overweight or obese.

  Figure 9. Dietary Guidelines for Americans: Healthy Weight Guidelines

  Another problem with defining a range of BMIs from 18.5 to 25 as healthy is that this “allows” you to gain a fair amount of weight and still stay in the healthy range. For example, a perfectly healthy thirty-year-old woman who is five feet six and weighs 130 pounds (BMI of 21) could gain twenty-five pounds and still be in the healthy range (BMI of 25). Yet this much added weight poses clear health risks.

  What about BMIs under 18.5, which the government’s tables say isn’t healthy? This can, indeed, signal an unhealthy weight, especially if an individual has been losing weight or has an eating disorder. Bu
t people who have maintained a low BMI for years while eating healthfully and being active are usually just fine and have no reason to increase their weight.

  KEEP YOUR BMI IN THE HEALTHY RANGE

  Here’s the bottom line on BMI: If your weight corresponds with a BMI below 25, do all you can to keep it there by healthy eating and exercising. More specifically, try to keep from gaining weight, even if you could add some pounds and still stay within the healthy BMI range. If your weight corresponds to a BMI above 25, you will do yourself a huge health favor by keeping it from increasing and, if possible, by trying to bring it down. If you inhabit the low end of the BMI curve and your weight hasn’t changed, great. But if you’ve been watching your weight slip downward and you aren’t dieting or trying to lose weight, check with your physician to pin down why this is happening.

  THE COLLEGE WEIGHT SCALE

  If you could travel back in time and stand next to your twenty-year-old self, how would you measure up? Older and wiser, to be sure. But how about around the waist or on the bathroom scale? It’s not an idle question: how much your weight and your waist have changed since your early twenties has a major bearing on your chances of staying healthy or developing a chronic disease.

  Adding a few pounds here and a few there during adulthood seems innocuous enough. It has its own catchy moniker—middle-age spread—and was once considered a sign of prosperity and success. It also seems to be an inevitable part of aging, affecting most Americans. In reality, adult weight gain is neither inevitable nor innocuous. In many cultures, gaining weight during adulthood just isn’t the norm. In Japan, for example, men and women—especially women—tend to stay the same weight throughout their adult years. On trips through Japan, I have often asked what would happen if a Japanese woman gained weight as she got older. The answer I usually get is a shocked “That would be one of the worst possible things for her.” Women in Sweden and France have also stayed slim, with obesity rates below 10 percent, far lower than among American women, about 40 percent of whom are obese.

  Even in the United States, we see clear differences in weight gain across different groups. For example, the less education people have, the more likely they are to be overweight or obese, especially men.9 There are also big geographic differences in obesity rates across the country.

  Gaining more than a few pounds after your early twenties can nudge you down the path toward chronic disease. The more weight, the harder the push. In the Nurses’ Health Study and the Health Professionals Follow-Up Study, middle-aged men and women who gained between 8 and 35 pounds after age twenty were two to three times more likely to have developed heart disease, high blood pressure, type 2 diabetes, and gallstones than their counterparts who gained 5 pounds or less.10 Larger weight gains meant even higher chances of developing these diseases.

  These studies and others that examine the relationship between weight and aging underscore this conclusion about the “healthy range” for weight and BMIs: someone who was lean at age thirty—say, with a BMI of 20—can gain more than 25 pounds and still stay in the healthy range, even though this weight gain has serious health consequences.

  APPLES AND PEARS

  Some people store much of their fat around the waist and chest; others store it around the hips and thighs. These two different body shapes have been dubbed “apple” and “pear.” Magazine articles and websites make a big fuss out of these arbitrary categories, and several websites use them as a key point in determining your health profile and risk of developing heart disease.

  Fat that accumulates around the waist and chest (often called abdominal adiposity) may pose more of a health problem than fat around the hips and thighs. Abdominal fat has been linked with high blood pressure, high cholesterol, high blood sugar, and heart disease. This fat, especially the fat inside the abdomen, may be generating more hormones and other chemicals that affect health than fat stored elsewhere. It is also possible that it isn’t doing this but instead is a signal about the harms of overall fatness that weight and height alone can’t describe. In a pooled analysis of cohort studies that included 650,000 men and women, a larger waist predicted a higher risk of premature death at every BMI.11

  Where, exactly, is your waist? For clothing designers, it’s the narrowest part of the torso. For scientists studying the health effects of body fat, it’s the region near the navel, where fat is typically deposited. The best way to measure your waist size is with the same two-step process used by researchers with the ongoing National Health and Nutrition Examination Survey: (1) Gently press your right hip bone to find its high point. (2) Place a tape measure just above that point and wrap the tape around your abdomen, keeping it parallel to the floor (see Figure 10). For most people, the top of the hip bone is generally in line with the navel. Others may need to pull the tape down a bit to the top of the hip bone.

  Measuring your waist can be useful because many people—particularly men—find themselves converting muscle to abdominal fat as they go through midlife. Even though weight may remain stable, an expanding waistline can be a warning sign of trouble on the horizon. So use your waist as a kind of low-tech biofeedback device—a waist-wise expansion of two or three inches over the years should trigger a warning that you need to reevaluate your diet and physical activity level. A waist size of 35 inches for women and 40 inches for men is a worrisome signal. As is the case with weight, it’s better to take action if your waist is increasing before you reach these limits.

  Some researchers advocate calculating a waist-to-hip ratio. That means dividing the size of your waist by the size of your hips. A waist-to-hip ratio greater than 0.90 for men and 0.85 for women can indicate the potential for health problems. But simply measuring your waist is probably just as useful. Many studies have shown that this single number is just as powerful at gauging the chances of developing chronic disease as the waist-to-hip ratio. It’s also a lot easier to do.

  Figure 10. Measuring Your Waist. To measure your waist, wrap a flexible measuring tape around your midsection where the sides of your waist are narrowest. This is usually even with the navel. Make sure you keep the tape parallel to the floor.

  WHY WE GAIN WEIGHT

  Your weight depends on a simple but easily unbalanced equation: weight change equals calories in minus calories out over time. Burn as many calories as you take in and your weight won’t change. Take in more than you burn and your weight increases. Dieting explores the other end of the spectrum: burning more calories than you take in.

  Chalk up why you’re the weight you are to a combination of what and how much you eat, your genes, your lifestyle, and your culture.

  • Your diet. What and how much you eat affects your weight. I will talk about this throughout the rest of the book.

  • Genes. Your parents are partly to blame, or to thank, for your weight and the shape of your body. Studies of twins raised apart show that genes have a strong influence on gaining weight or being overweight, meaning that some people are genetically predisposed to gaining weight. Heredity plays a role in the tendency to store fat around the chest, waist, or thighs. It is possible that some people are more sensitive to calories from fat or carbohydrates than others, although the evidence for this is thin. I must stress the phrase “partly to blame,” however, because genetic influences can’t explain the rapid increase in obesity seen in the United States over the last thirty years or the big differences in obesity rates among countries.

  It’s likely that our prehistoric ancestors shaped our physiological and behavioral responses to food. Early humans routinely coped with feast-or-famine conditions. Since it was impossible to predict when the next good meal might appear—like a patch of ripe berries or a catchable antelope—eating as much as possible whenever food was available might have been a key to surviving the lean times. This survival adaptation means that complex chemical interactions between body and mind that evolved eons ago in response to routine periods of starvation may drive us to eat whenever possible. In this era of plent
y, that means all the time.

  • Lifestyle and physical activity. If eating represents the pleasurable, sensuous side of the weight change equation, then metabolism and physical activity are its nose-to-the-grindstone counterparts. Your resting (basal) metabolism is the energy needed just to breathe, pump and circulate blood, send messages from brain to body, maintain your temperature, digest food, and keep the right amount of tension in your muscles. It typically accounts for 60 to 70 percent of your daily energy expenditure. Physical activity makes up most of the rest. If you work a desk job and do little more than walk from your car to your office and back again, you may burn ridiculously few calories a day.

  • Culture. Ours is a culture of living large, of Texas-size appetites where quantity often edges out quality. Indulgence is tolerated, even revered. Love is food, and food is love: Imagine your grandmother urging you to have another helping or the pleasurable groans and belt loosening that end many holiday and regular meals. These are not universal tendencies. In France and throughout much of Asia, the cuisine emphasizes quality and presentation, not how much food can be crammed on a plate or into your belly. People in many cultures also believe it is inappropriate or downright rude to eat until you are full, and teach their children to eat to 70 percent of capacity.

  • Family and friends. In a book called Thinfluence12 that I coauthored with Dr. Malissa Wood, a cardiologist and health promotion expert, and Dan Childs, we described the many layers of our social environments that nudge us away from or toward better weight control. Our family and friends, where we work and play, and other social factors strongly influence what and how much we eat. Making healthy choices can be challenging when everyone around is filling up on sugary soda and pizza and no healthful foods are in sight. In Thinfluence we also describe how individuals can change or circumvent the factors working against them, for their own well-being and for those around them.