In January 2013 a study looking at the relationship between body weight and mortality rates got lots of press, and for good reason. It was published in the Journal of the American Medical Association (JAMA).
The researchers, from the Centers for Disease Control and Prevention (CDC) and elsewhere, pooled data from 97 studies done in more than a dozen countries, totaling nearly 3 million people. The surprising results: Overweight people were found to have a 6 percent lower overall death rate than people of “normal” weight. The data were adjusted for age, gender and smoking.
And while moderately or severely obese people were 29 percent more likely to die during a given period, the mildly obese were at no greater risk than normal-weight people. For people over 65, the mortality benefit of carrying some extra pounds seemed to be most notable.
Research on this subject has produced mixed results. This was not the first analysis to indicate that being overweight may be the “sweet spot” on the weight spectrum, especially for older people, but it is the largest and most rigorous study so far.
Commentators had a field day with the news, lambasting “overzealous” health experts who’ve warned about the dangers of the obesity epidemic. In contrast, others worried that junk-food companies would use the study to encourage consumers to forget about weight control and healthy eating.
But the picture is not black and white. Before you stock up on ice cream and doughnuts and cancel your gym membership, it’s important to look at the bigger picture.
Defining weight categories
First of all, what is normal, overweight or obese? That, of course, is the crux of the matter. The JAMA study used standard ranges based on body mass index, or BMI. About one-third of Americans are overweight, one-third obese and one-third normal weight or underweight, by these definitions.
BMI is calculated by dividing weight (in kilograms) by height (in meters) squared. Here’s an easier way to compute it: Multiply your weight (in pounds) by 705; divide the result by your height (in inches); then divide again by your height. This government website will compute your BMI for you.
There has been ongoing debate about these numbers and what optimal or healthy weight is. Before 1998, when the current federal guidelines were released, the cutoffs for weight categories were higher. These lines are hard to draw, and the new study (as well as some other research) suggests that the “normal” range may now be too low. In any case, the cutoffs for BMI and other measures of body weight are based on population averages and are thus imperfect tools for evaluating an individual’s risk.
|BMI range||5'3" person||5'10" person|
|Underweight||less than 18.5||less than 105 pounds||less than 130 pounds|
|Normal weight||18.5 to 24.9||105 to 140||130 to 175|
|Overweight||25 to 29.9||140 to 170||175 to 210|
|Obese, grade 1 (mild)||30 to 34.9||170 to 200||210 to 245|
|Obese, grade 2 (moderate)||35 to 39.9||200 to 225||245 to 280|
|Obese, grade 3 (severe)||greater than 40||greater than 225||greater than 280|
The good news
One thing this study makes clear is that fewer Americans are dying of obesity-related illnesses than would be expected, particularly after age 65. Why? While there’s no dispute that obese people, on average, are still at much higher risk for developing coronary artery disease, hypertension and diabetes than thinner people, medication can control these and many other disorders. Doctors may be more aggressive in managing risk factors in obese people. Plus, when people do have heart attacks, strokes and other adverse events, there are better medical treatments to keep them alive. One remarkable result is that death rates from coronary artery disease have been cut by two-thirds since 1980. All this has weakened the link between obesity and mortality.
The bad news
Clearly, at some point—above a BMI of 35 in the JAMA study—obesity shortens lives. But it’s a mistake to focus only on mortality rates, which are just the tip of the iceberg. Even when they don’t kill people, the disorders that are caused or worsened by obesity—from heart attacks, strokes and diabetes to kidney disease and osteoarthritis of knees and hips—impair quality of life and increase disability, not to mention boosting health care costs. Being unable to climb a flight of stairs without pain, walk a mile or lift your luggage are not minor matters.
Similarly, being too thin can also be bad—or at least be a marker for poor health. People with serious conditions tend to lose weight (fat and muscle), which worsens their prognosis; smokers also tend to weigh less than nonsmokers. Both groups inflate death rates in the normal-weight category. Sick obese older people tend to live longer than their sick thinner counterparts, in part because they have greater energy reserves. That’s an added complication when evaluating the links between weight, health and longevity. If the normal-weight category includes a disproportionate number of people who have lost weight due to illness, that would distort the overall risk ratios.
Thus, some experts think that “normal” BMI should exclude the lowest segment (which may be too thin) and begin at 20 or 22 rather than 18.5. Most studies have found that BMIs between 22 and 25 are associated with greatest longevity, according to the accompanying editorial in JAMA.
The confusing news
Calculating the adverse effects of being overweight or obese is complex, and this study is not the last word. The fact is, no one knows how many people die as a result of obesity per se. Obese people often have a poor diet and are sedentary, so it’s hard to tell whether it’s obesity itself that puts them at increased risk.
Previous research has found that if you’re obese and stay physically fit and thus “metabolically healthy” (that is, have normal blood pressure, blood sugar and cholesterol levels), you’re actually less likely to die prematurely than those who are thin and sedentary.
Where you pack on the extra fat also matters. Excess fat in the abdominal area (as in an “apple-shaped” body), especially if it surrounds internal organs, is linked to cardiovascular disease, diabetes and some cancers. Meanwhile, fat in the thighs and hips (“pear-shaped” body) is not a health problem and may even be protective. That’s why waist measurement is considered a good indicator of risk.
Bottom line: Optimal weight depends on many factors—notably your fitness level, body shape, family history and your risk for various diseases. If you are 5'10" and weigh 195 pounds, clearly you’re overweight, but if you exercise regularly, don’t smoke and are healthy in other respects, you probably don’t need to make big changes. On the other hand, if you have high blood pressure, blood sugar or cholesterol, one of the most important things you can do is lose weight—even 10 pounds can make a difference. You can, of course, just take medication for these problems, but weight loss is still beneficial.
For many people, the main problem with being simply overweight or slightly obese is that they continue to gain more weight. Obesity is epidemic in America and many other countries, increasing even among children. Thanks to medical advances, we are better at treating obese people, thus prolonging their lives. But the cost, in health care dollars and quality of life, is great.