Introduction: Obesity and Health Risks

When it comes to nutrition, it’s easy to spend a lot of time worrying about what to eat. But how much you eat puts as much of a stamp on your long-term health as picking the right kind of fat or choosing the right mix of vitamins.

How much you weigh (in relation to your height), your waist size, and how much weight you’ve gained since your mid-20s strongly influence your chances of:

• dying early,
• having, or dying from, a heart attack, stroke, or other type of cardiovascular disease,
• developing diabetes,
• developing cancer of the colon, kidney, breast, or endometrium,
• having arthritis,
• developing gallstones,
• being infertile,
• developing asthma as an adult,
• snoring or suffering from sleep apnea,
• developing cataracts, or
• having a poorer quality of life.

Although researchers are quibbling about just how many people die each year as a direct cause of excess weight and what it costs our health-care system, excess weight takes an enormous toll—all the more worrisome, given that we are in the midst of an obesity epidemic.

If your weight is in the healthy range and isn’t more than 10 pounds over what you weighed when you turned 21, great. Keeping it there—and keeping it steady—by watching what you eat and exercising will limit your risk of developing one or more of the chronic conditions noted above. If you are overweight, doing whatever you can to prevent gaining more weight is a critical first step. Then, when you’re ready, shedding some pounds and keeping them off will be important steps to better health.

What’s a Healthy Weight? Body Mass Index (BMI) Defined

Although nutrition experts still debate the precise limits of what constitutes a healthy weight, there’s a good working definition based on the ratio of weight to height. This ratio, called the body mass index (or BMI for short), takes into account the fact that taller people have more tissue than shorter people, and so tend to weigh more.

Here’s how to determine your body mass index: Divide your weight in pounds by your height in inches. Divide the answer by your height in inches. Multiply the answer by 703. For an easier way, the National Heart, Lung and Blood Institute offers an online BMI calculator or simple BMI tables.

Dozens of studies that have included more than a million adults have shown that a body mass index above 25 increases the chances of dying early, mainly from heart disease or cancer, and that a body mass index above 30 dramatically increases the chances. Based on this consistent evidence, a healthy weight is one that equates with a body mass index less than 25. By convention, overweight is defined as a body mass index of 25 to 29.9, and obesity is defined as a body mass index of 30 or higher.

Nothing magical happens when you cross from 24.9 to 25 or from 29.9 to 30. These are just convenient reference points. Instead, the chances of developing a weight-related health problems increases across the range of weights.

Muscle and bone are more dense than fat, so an athlete or muscular person may have a high body mass index, but not be fat. It’s this very thing that makes weight gain during adulthood such an important determinant of weight-related health—few adults add muscle and bone after their early twenties, so nearly all that added weight is fat.

Waist Size Matters, Too: Abdominal Fat and Health Risks

Some research suggests that not all fat is created equal. Fat that accumulates around the waist and chest (what’s called abdominal obesity or abdominal adiposity) may be more dangerous for long-term health than fat that accumulates around the hips and thighs.

Some studies suggest that abdominal fat plays a role in the development of insulin resistance and inflammation, an overactivity of the immune system that has been implicated in heart disease, diabetes, and even some cancers. It’s also possible, of course, that abdominal fat isn’t worse than fat around the hips or thighs, but instead is a signal of overall body-fat accumulation that weight alone just doesn’t capture.

In people who are not overweight, waist size may be an even more telling warning sign of increased health risks than BMI.  The Nurses’ Health Study, for example, looked at the relationship between waist size and death from heart disease, cancer, or any cause in middle-aged women. At the start of the study, all 44,000 study volunteers were healthy, and all of them measured their waist size and hip size. After 16 years, women who had reported the highest waist sizes—35 inches or higher—had nearly double the risk of dying from heart disease, compared to women who had reported the lowest waist sizes (less than 28 inches). Women in the group with the largest waists had a similarly high risk of death from cancer or any cause, compared with women with the smallest waists. The risks increased steadily with every added inch around the waist. And even women at a “normal weight”—BMI less than 25—were at a higher risk, if they were carrying more of that weight around their waist: Normal-weight women with a waist of 35 inches or higher had three times the risk of death from heart disease, compared to normal-weight women whose waists were smaller than 35 inches. The Shanghai Women’s Health study found a similar relationship between abdominal fatness and risk of death from any cause in normal-weight women.

 Waist vs. Waist-to-Hip RatioScientists have long debated about which measure of abdominal fat best predicts health risk: waist size alone, or waist size in comparison to hip size.

Measuring your waist is easy, if you know exactly where your waist really is. Wrap a flexible measuring tape around your midsection where the sides of your waist are the narrowest. This is usually even with your navel. Make sure you keep the tape parallel to the floor.

An expert panel convened by the National Institutes of Health concluded that a waist larger than 40 inches for men and 35 inches for women increases the chances of developing heart disease, cancer, or other chronic diseases. (4) Although these are a bit generous,  they are useful benchmarks.

Waist size is a simple, useful measurement because abdominal muscle can be replaced by fat with age, even though weight may remain the same. So increasing waist size can serve as a warning that you ought to take a look at how much you are eating and exercising.

Keeping Things Level

Middle-aged spread is the source of millions of New Year’s resolutions. Gaining weight as you age increases the chances of developing one or more chronic diseases.

In the Nurses’ Health Study and the Health Professionals Follow-up Study, middle-aged women and men who gained 11 to 22 pounds after age 20 were up to three times more likely to develop heart disease, high blood pressure, type 2 diabetes, and gallstones than those who gained five pounds or fewer. Those who gained more than 22 pounds had an even larger risk of developing these diseases.  A more recent analysis of Nurses’ Health Study data found that adult weight gain—even after menopause—can increase the risk of postmenopausal breast cancer.  Encouragingly, for women who had never used hormone replacement therapy, losing weight after menopause—and keeping it off—cut their risk of post-menopausal breast cancer in half.

What Causes Weight Gain?

Whether or not your weight changes depends on a simple rule:

Weight change = calories in – calories out

If you burn as many calories as you take in each day, there’s nothing left over for storage in fat cells and weight remains the same. Eat more than you burn, though, and you end up adding fat and pounds.

Many things influence what and when you eat and how many calories you burn. These turn what seems to be a straightforward pathway to excess weight into a complex journey that may start very early in life.

A growing body of research suggests that there’s a link between how much people sleep and how much they weigh. In general, children and adults who get too little sleep tend to weigh more than those who get enough sleep.  Learn more about the relationship between sleep and obesity.

Genes: Some people are genetically predisposed to gain weight more easily than others or to store fat around the abdomen and chest. It’s also possible that humans have a genetic drive to eat more than they need for the present in order to store energy for future. This is called the thrifty gene hypothesis.  It suggests that eating extra food whenever possible helped early humans survive feast-or-famine conditions. If such thrifty genes still exist, they aren’t doing us much good in an environment in which food is constantly available.

Diet: At the risk of stating the obvious, the quantity of food in your diet has a strong impact on weight. The composition of your diet, though, seems to play little role in weight—a calorie is a calorie, regardless of its source.

Physical activity: The “calories burned” part of the weight-change equation often gets short shrift. The more active you are, the more calories you burn, which means that less energy will be available for storage as fat. Exercising more also reduces the chances of developing heart disease, some types of cancer, and other chronic diseases.  In other words, physical activity is a key element of weight control and health.

What Leads to Weight Loss?

Just as weight gain is fundamentally caused by eating more calories than you burn, the only way to lose weight is to eat fewer calories than what you burn. People can cut back on calories and lose weight on almost any diet, as long as they stick to it.  (Read about the latest diet study showing the importance of finding a diet that you can follow, so you can stick to a low-calorie plan and lose weight.) The real challenge is finding a way to keep weight off over the long run.

Low-fat weight loss strategies don’t work for most people. Low-fat diets are routinely promoted as a path to good health. But they haven’t fulfilled their promise. One reason is that many people have interpreted the term “low-fat” to mean “It’s OK to eat as much low-fat food as you want.” For most people, eating less fat has meant eating more carbohydrates. To the body, calories from carbohydrates are just as effective for increasing weight as calories from fat.

In the United States, obesity has become increasingly common even as the percentage of fat in the American diet has declined from 45 percent in the 1960s to about 33 percent in the late 1990s.  In South Africa, nearly 60 percent of people are overweight even though the average diet contains about 22 percent of calories from fat.  Finally, experimental studies lasting one year or longer have not shown a link between dietary fat and weight.  And in the eight-year Women’s Health Initiative Dietary Modification Trial, women assigned to a low-fat diet didn’t lose, or gain more weight than women eating their usual fare.

Low-carbohydrate, high-protein strategies look promising in the short term. Another increasingly common approach to weight loss is eating more protein and less carbohydrate. Some of these diets treat carbohydrates as if they are evil, the root of all body fat and excess weight. That was certainly true for the original Atkins diet, which popularized the no-carb approach to dieting. And there is some evidence that a low-carbohydrate diet may help people lose weight more quickly than a low-fat diet, although so far, that evidence is short term.  More recently, a two-year head-to-head trial comparing different weight loss strategies found that low-carb, low-fat, and Mediterranean-style diets worked equally well, and that there was no speed advantage for one diet over another. 

Q. What are the best fruits and vegetables to eat if I want to lose weight? Dr. Walter Willett, Chair, Dept. of Nutrition, Harvard School of Public HealthA. Chose a wide variety of vegetables and fruits every day, but don’t include white potatoes as a vegetable. Potatoes are a rapidly digested starch; nutritionally, they have more in common with white bread than with other vegetables, and they should be eaten only occasionally. Go easy on fruits that are higher in carbohydrate—oranges, bananas, apricots, cherries, grapes, mangoes, pineapples, and pears. Also, avoid fruit juice since it contains a lot of sugary calories; choose whole fruit instead since it has more fiber and will make you feel more full. Why, in some studies, do high-protein, low-carb diets seem to work more quickly than low-fat, high-carbohydrate diets, at least in the short term? First, chicken, beef, fish, beans, or other high-protein foods slow the movement of food from the stomach to the intestine. Slower stomach emptying means you feel full for longer and get hungrier later. Second, protein’s gentle, steady effect on blood sugar avoids the quick, steep rise in blood sugar and just as quick hunger-bell-ringing fall that occurs after eating a rapidly digested carbohydrate, like white bread or baked potato. Third, the body uses more energy to digest protein than it does to digest fat or carbohydrate.

No one knows the long-term effects of eating little or no carbohydrates. Equally worrisome is the inclusion of unhealthy fats in some of these diets.

If you want to go the lower-carb route, try to include some fruits, vegetables, and whole-grain carbohydrates every day. They contain a host of vitamins, minerals, and other phytonutrients that are essential for good health and that you can’t get out of a supplement bottle. Choosing vegetable sources of fat and protein may also lower your risk of heart disease and type 2 diabetes.

Mediterranean-style diets may be effective. Eating a so-called Mediterranean-style diet—one that includes plenty of fruits and vegetables and that is low in saturated fat but has a moderate amount of unsaturated fat—offers another seemingly effective alternative. In a controlled trial conducted by researchers at Harvard-affiliated Brigham and Women’s Hospital, 101 overweight men and women were randomly assigned to a low-fat diet or a Mediterranean-style diet. After 18 months, volunteers on the low-fat diet had gained an average of 6 pounds while those on the Mediterranean diet lost 9 pounds.  By the study’s end only 20 percent of those in the low-fat group were still following the study diet, compared to more than half of those on the Mediterranean-style diet. Other trials have also found a Mediterranean-style eating plan to be effective for weight loss. 

Since 1993, more than 5,000 women and men have joined the National Weight Control Registry. This select “club” includes only people who lost more than 30 pounds and kept them off for at least a year. What was their secret?

• They exercised. Registry participants burn an average of 400 calories per day in physical activity. That’s the equivalent of about 60 to 75 minutes of brisk walking, or 35 to 40 minutes of jogging.
• They ate fewer calories. On average, registry volunteers consume about 1,400 calories a day. That’s significantly less than the calories consumed by the average American. This doesn’t mean, however, that you should aim for 1,400 calories a day. What’s right for you is based on your weight, height, and activity level.
• They watched less television, limited fast food intake, cut back on sugars and sweets, and ate more fruits and vegetables.

In the early years of the registry, about a third of the volunteers reported eating low-fat diets. Lately, though, fewer volunteers report eating low-fat diets, and more report eating moderate-fat diets. Relatively few volunteers report eating low-carbohydrate diets, but those who do seem to have had as much success in maintaining their weight loss, compared with other members of the Weight Control Registry.

 Q. Can diet pills or gastric bypass surgery help me lose weight?A. The promise of a quick fix for excess weight has always attracted Americans. But drugs and gastric bypass surgery are not for everyone.

These findings are echoed in a survey of more than 32,000 dieters reported in the June 2002 issue of Consumer Reports.  Nearly one-quarter had lost at least 10 percent of their starting body weight and kept it off for at least a year. Most chalked up their success to eating less and exercising more. The vast majority did it on their own, without utilizing commercial weight-loss programs or resorting to weight-loss drugs. Interestingly, the successful losers in the Consumer Reports survey tended to adopt low-carbohydrate, higher-protein diets rather than low-fat diets.

Keep in mind that these are commonly used strategies, not hard and fast rules. In fact, one of the main take-home messages is that successful weight loss is very much a “do it your way” endeavor. What the Weight Control Registry volunteers and the Consumer Reports survey respondents have in common is a focus on exercise and daily calories. In other words, they’ve learned to balance energy in and energy out in a way that leads to weight loss or weight maintenance.

So despite all the pessimistic prognostications about the impossibility of sticking with a weight-loss plan, these two surveys show that it’s possible to lose weight and keep it off. Unfortunately, only a minority of people who try to lose weight follow the simple, tried-and-true strategy of eating fewer calories and exercising daily. For weight control, an hour or more of exercise a day may be needed.

General Strategies for Achieving or Maintaining a Healthy Weight

It’s easy to gain weight in what Yale psychologist Kelly Brownell calls our “toxic food environment.” How, then, can you lose weight if you need to? Here are some suggestions that work:

• Set a realistic goal. Many people pick weight goals they’ll have a hard time achieving, like fitting into a size 8 dress or a wedding tuxedo from 20 years ago. A better initial goal is 5 to 10 percent of your current weight. This may not put you in league with the “beautiful people” profiled in popular magazines, but it can lead to important improvements in weight-related conditions such as high blood pressure and diabetes.  You don’t have to stop there, of course. You can keep aiming for another 5 to 10 percent until you’re happy with your weight. By breaking weight loss into more manageable chunks, you’ll be more likely to reach your goal.
• Slow and steady wins the race. Dieting implies deprivation and hunger. You don’t need either to lose weight if you’re willing to take the time to do it right. If you cut out just 100 calories a day, the equivalent of a single can of soda or a bedtime snack, you would weigh 10 pounds less after a year. If, at the same time, you added a brisk 30-minute walk five days a week, you could be at least 20 pounds lighter.
• Move more.While the precise amount of physical activity needed to maintain a healthy weight may vary based on your diet and your genes, the American College of Sports Medicine and the American Heart Association conclude that “more activity increases the probability of success.”  For more tips on fitting physical activity into your day, read Staying Active: Every Body’s Path to Better Health.
• Keep track. It’s easy to eat more than you plan to. A daily food diary can make you more aware of exactly how much you are eating. Include everything, no matter how small or insignificant it seems. Small noshes and drinks of juice add up to real calories.
• Tame your blood sugar. Eating foods that make your blood sugar and insulin levels shoot up and then crash may contribute to weight gain. Such foods include white bread, white rice, and other highly processed grain products. As an alternative, choose foods that have a gentler effect on blood sugar (what’s called a lower glycemic index). These include whole grains such as wheat berries, steel-cut oats, and whole-grain breads and pasta, as well as beans, nuts, fruits, and vegetables.
• Don’t be afraid of good fats. Fat in a meal or in snacks such as nuts or corn chips helps you feel full. Good fats such as olive or canola oil can also help improve your cholesterol levels when you eat them in place of saturated or trans fats or highly processed carbohydrates.
• Reach for slow foods. Fast food is cheap, filling, and satisfying. It also delivers way more calories, not to mention harmful saturated and trans fat, than you need. People who eat at fast-food restaurants more than twice a week are more likely to gain weight and show early signs of diabetes than those who only occasionally eat fast food.
• Bring on the water and skip the soda. When you are thirsty, reach for water. Drinking juice or sugared soda can give you several hundred calories a day without even realizing it. Several studies show that children and adults who drink soda or other sugar-sweetened beverages are more likely to gain weight than those who don’t,  and that switching from these to water or unsweetened beverages can reduce weight.

The Bottom Line: Recommendations for Healthy Weight

What’s sometimes lost in the dire predictions about overweight and obesity in America are the enormous benefits of staying lean or working toward a healthier weight. Maintaining a healthy weight throughout life is associated with lower rates of premature death and heart disease, some cancers, and other chronic conditions. What if you’re past that point? Losing 5 to 10 percent of your weight can substantially improve your immediate health and will decrease your risk of developing such problems. The best time to start losing weight is with the first signs that your weight is straying upward. The more overweight you are, the more difficult it can be to lose weight. But as participants of the National Weight Control Registry have proven, anyone can lose weight.