Is it OK to be overweight?

(MoneyWatch) The prestigious Journal of the American Medical Association recently released a study prepared by researchers at the Centers for Disease Control (CDC) that showed there were fewer deaths among people whose body mass index (BMI) was considered overweight compared to people with a BMI indicating normal weight.

This got my attention, since being overweight or obese has been linked by many studies with increased chronic illnesses, higher medical costs and reduced life expectancies. Should we ditch our New Year's resolution to lose weight, throw away the diet books and reach for a six-pack and a package of Twinkies? Not so fast. Let's dig a little deeper into the survey results.

What is BMI?

To understand the results of the CDC study, you'll need to know the different categories of the BMI measurements. That index measures your weight relative to your height and is a crude approximation of how much you should weigh given how tall you are. The simplest versions of BMI calculators, including one from the Centers for Disease Control, use just your weight and height to determine your BMI.

A BMI of 18.5 to 24.9 is considered normal; values from 25 to 29.9 are considered overweight. BMIs under 18.5 are considered underweight, and values that are 30 and above are considered obese. To be more specific, BMIs of 30 to 34.9 are considered grade 1 obese, BMIs of 35 to 39.9 are considered grade 2 obese, and values of 40 and higher are considered grade 3 obese.

The CDC study was a meta-analysis of 97 different studies that related mortality to BMI, covering roughly 2.9 million people. In summary, the study found slightly reduced mortality -- about 6 percent less -- among those who were overweight (BMIs between 25 and 29.9) compared to people with BMIs that indicated normal weight. Significantly higher mortality was reported for all people classified as obese (BMIs greater than 30), but most of the additional mortality was concentrated in BMI obesity values that are considered grades 2 and 3 (BMIs higher than 35). No significant additional mortality was reported for grade 1 obesity, which is a BMI between 30 and 34.9.

The CDC study reported that when possible, it adjusted for such factors as smoking and health conditions that could result in higher deaths being reported for lower BMI values.

What the study found

Before you think it's OK to be overweight, consider that the CDC study only measured differences in mortality rates, not illness. So it's possible that people are living longer but are actually sicker. In fact, that possibility is suggested by one meta-analysis conducted by the Society of Actuaries of more than 500 studies that linked obesity to increased disease. That study showed that for both groups -- those with BMIs in the overweight and obese ranges -- medical costs were higher and there was increased risk for hypertension, heart disease, stroke, diabetes and gall bladder disease as compared to those with normal BMI values.

Also consider that the BMI measurement has long been considered a crude measure of healthy weight; while one advantage is that it's easy to measure, it can produce misleading results. For example, healthy athletes can record a high BMI, since muscle weighs more than fat. And people who smoke or who have a disease that reduces weight, such as cancer, may have a low BMI. The BMI also doesn't consider factors such as the type of foods you eat or the amount of exercise you get, both of which have a significant impact on your health.

Instead of relying just on your own BMI as an indicator of your health, you'd be better off taking the time to obtain measures that more accurately assess your health risks, such as blood pressure, cholesterol counts, blood sugar counts, body-fat percentage, heart rate and waist circumference. People over age 50 should be monitoring these measurements with annual or biannual physicals. While this may sound like a lot of trouble, I can personally attest that it's well worth your time to monitor your health.

Only one measure

So consider the BMI just one measure of your health, and put it into a broader context. For example, don't feel complacent if your BMI is in the normal range yet you have other poor health habits, such as smoking, abusing alcohol or eating a lot of fatty foods. And certainly don't rush to put on some pounds if your BMI is low or normal, thinking it will reduce your risk of death. The small difference in mortality rates between people with normal and overweight BMI values could be the result of a number of factors that have nothing to do with your health.

Similarly, if you have a BMI that's considered overweight, use that as motivation to investigate more accurate health measures. You may find that other measures indicate that you're healthy, in which case you can relax about your weight. You might even improve your wellness by being less stressed by your weight and avoiding diets that produce wide swings in your weight. But if other health measures show cause for concern, or if your BMI puts you in the obese category, particularly grade 2 or 3, consider that to be a red flag that requires corrective action from you.

The bottom line: Keep your New Year's resolution. Don't draw unhealthy conclusions from the headlines.

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    Steve Vernon helped large employers design and manage their retirement programs for more than 35 years as a consulting actuary. Now he's a research scholar for the Stanford Center on Longevity, where he helps collect, direct and disseminate research that will improve the financial security of seniors. He's also president of Rest-of-Life Communications, delivers retirement planning workshops and authored Money for Life: Turn Your IRA and 401(k) Into a Lifetime Retirement Paycheck and Recession-Proof Your Retirement Years.