In the Dietary Guidelines for Americans, healthy weights are those corresponding to BMIs between 18.5 and 25. BMIs above 25 are clearly labeled as unhealthy, but the guidelines dodge the issue of setting a lower healthy limit by not putting any label on BMIs below 18.5. (See Figure 6.)
In choosing these limits, the committee charged with setting the guidelines tried to balance scientiﬁc evidence with public policy and perception. That’s a diﬃcult job, because there is no simple breakpoint between healthy and unhealthy weights. Panel members agreed that the risk of heart disease, diabetes, and high blood pressure begins to climb at BMIs 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. Thus almost everyone with a BMI over 25—except for extremely muscular body builders—would be healthier with a lower BMI, but many people with a BMI of 23–25 are not at their healthiest weight. Still, drawing the line at 25 means that two-thirds of adult Americans are overweight or obese.
FIG. 6 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 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), whereas this much added weight poses clear health risks.
KEEP YOUR BMI LOW
The bottom line on healthy weight is this: If your weight corresponds with a BMI below 25, do everything you can to keep it there. 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 getting larger 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.
learn more: Eat, Drink, and Be Healthy!
Adding a few pounds here, 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 a trip through Japan, I asked what would happen if a Japanese woman gained weight as she got older. The answer was a shocked “That would be one of the worst possible things for her.” Even in the United States, we are beginning to see clear cultural diﬀerences in weight gain. The more education people have, the less likely they are to be overweight or obese.
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 two long-term Harvard studies, the Nurses’ Health Study and the Health Professionals Follow-up Study, middle-aged men and women who had gained between eleven and twenty-two pounds after age twenty were up to three times as likely to develop heart disease, high blood pressure, type 2 diabetes, and gallstones as their counterparts who gained ﬁve pounds or less. Larger weight gains meant even higher chances of developing these diseases.
These studies and others point to one of the big problems with the “healthy range” for weight and BMIs. Someone who was lean at age twenty—say, with a BMI of 19—can gain more than twenty-ﬁve pounds and still stay in the healthy range, even though this weight gain has serious health consequences.
WHY WE GAIN WEIGHT
Your weight depends on a simple but easily unbalanced equation: Weight change equals calories in minus calories out. 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— consuming fewer calories than you burn.
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 in the rest of the book.
• Genes. Your parents are partly to thank, or to blame, 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 and waist. It is also possible that some people are more sensitive to calories from fat or carbohydrates than others, though the evidence for this is still thin. I must stress the phrase partly to blame, though, 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 possible 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 ripe patch of berries or a catchable antelope—eating as much as possible whenever food was available may have been a key to surviving the lean times. This survival adaptation means that complex chemical interactions between body and mind that evolved aeons ago in response to routine periods of starvation may drive us to eat whenever possible. In this era of plenty, that means all the time.
• Lifestyle. 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.
learn more: Building a Better Pyramid
• 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— just 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. 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.
On top of that, we have what I call the overproduction problem. U.S. farmers produce 3,800 calories’ worth of food a day for every man, woman, and child in America. That’s nearly double what the average person needs. The almost inevitable consequence of this surfeit is a system that encourages full-tilt consumption: Producers and food manufacturers want us to eat more of their products, and they are competing with one another to exploit our weaknesses. The food industry spends tens of billions of dollars a year learning the best ways to entice us and then acting on that knowledge. The keen senses we have inherited for salt and sweetness that were once needed for survival (our taste for sweet things, for example, helped early humans sort through leaves to ﬁnd the tender young ones with a ready supply of energy) are continually exploited. The sugar and salt content of products have been ratcheted up to increase our expectations for sweetness and saltiness and get us to eat, and buy, more. What’s more, food is sold everywhere—gas stations sell doughnuts and sandwiches, bookstores and department stores oﬀer coﬀee and sweets, and you can get full, belly-busting meals at baseball and other sporting events. Restaurants have also gotten into the act. The modest portions of nouvelle cuisine have been overshadowed by supersizing, and it isn’t uncommon to be served a meal that contains 1,500 to 2,000 calories, about what you need for an entire day.
This incredible access to food and the nearly unlimited
variety of food tests the willpower of even the most sensible eater. When combined with too little physical activity, it’s a sure recipe for weight gain. And because weight control is the single most important factor in your good health (after not smoking), overeating can pose serious health risks.