We constantly hear that obesity is a killer and that the obesity epidemic will surely sink our health care system — but are a few extra pounds really bad for your health? A recent study suggests that being a little overweight may actually reduce your chance of dying. Hear us out, though, before scarfing some cookies in celebration!
First, a few words about Body Mass Index (BMI), also sometimes called the Quetelet Index. Devised in the mid-1800’s by the Belgian polymath, Aldolphe Quetelet, the index is defined as the individual’s body weight (e.g., mass) divided by the square of their height. (Find out your BMI athttp://www.nhlbi.nih.gov/guidelines/obesity/BMI/bmicalc.htm). The BMI is commonly used to determine if someone’s weight is defined to be underweight (BMI <18.5), normal (BMI 18.5–24.9), overweight (BMI 25–29.9), or obese (BMI > 30). But, these categories have changed over time, and the BMI can be misleading because it doesn’t indicate how much of someone’s weight is made up of body fat (adipose tissue) versus muscle; a 150-pound athlete is likely to have less fat on her than a 120-pound couch potato.
A recent study by Dr. Katherine Flegal of the Centers for Disease Control and Prevention (CDC) analyzed all published studies that looked at the BMI and compared their reported death rates for standard BMI categories for general populations of adults.1 Her comprehensive analysis included 97 studies with more than 2.88 million individuals from North America, Europe, Australia, China, Taiwan, Japan, Brazil, Israel, and Mexico. In all, 270,000 deaths were analyzed.
The study confirmed that severe obesity is clearly bad for your health; someone with a BMI over 35 is at increased risk of dying. For a 5’ 5” woman (the average height for American women), a BMI of 35 would equal a weight of 210 pounds. But, the study found that a 5’ 5” woman who weighed 180 pounds — a BMI of 30 — was not at increased risk of dying, even though the BMI categorizes her as “obese.” The same woman, by the way, would be classified as “overweight” if she topped 150 pounds.
In Flegal’s study, not only was a BMI that qualified a person to be obese or overweight not associated with increased risk of mortality, but these BMIs were actually also associated with decreased risk of dying. Flegal’s analysis has been criticized because it included smokers and people with chronic diseases, both of which can cause people to lose weight. But cherry-picking study subgroups can also result in a biased assessment.
Flegal points out that it’s important to compare actual BMIs between studies rather than comparing people classified as overweight or obese. It’s a good point because what counts as obese has changed over time. When you hear that obesity in the U.S. has skyrocketed in the last 20 years, keep in mind that this epidemic is due partly to reclassification. In 1998, the number of overweight and obese individuals in the U.S. increased by 37 million in one day. Why? Because that day, the terms were redefined by a National Institutes of Health (NIH) “expert panel:” “overweight” was redefined as a BMI over 25, and “obese” was expanded to include anyone with a BMI over 30.2
As it turns out, nearly 90 percent of these NIH panel members had financial ties to the weight-loss industry, including pharmaceutical companies and weight-loss clinics.3 The panel chair, Xavier Pi-Sunyer, served as President of the North American Association for the Study of Obesity (NAASO, also called the Obesity Society), an industry-funded group. The year after chairing the panel, Pi-Sunyer was identified in a lawsuit as the guest author of a ghostwritten review on obesity commissioned by Wyeth-Ayerst regarding long-term, off-label use of the dangerous “fen-phen” combination (fenfluramine and phentermine).3
In 2004, the CDC reported that obesity caused 400,000 deaths annually. Although this estimate was reduced after a Congressional inquiry, Medicare nonetheless announced that it would treat obesity as a disease, enabling Federal reimbursement for anti-obesity treatments. U.S. Surgeon General Richard Carmona subsequently announced, “Obesity is the terror within…the magnitude of the dilemma will dwarf 911 or any other terrorist attempt.”3 Yet, when a group of CDC researchers reanalyzed the data and adjusted for confounding factors, it found only 25,814 annual, obesity-related deaths — less than seven percent of the original estimate.
In fact, some of the risks associated with obesity may actually be due to other factors. Obesity can be a marker for low socioeconomic status, lack of exercise, poor nutrition, or depression, all of which can affect health status. Heavy people may also go on drastic diets, take drugs, or have surgery to lose weight, which makes it difficult to separate the health risks of obesity from the health risks of therapies for obesity.
One of us was recently bragging, over dessert, about how she doesn’t have to worry about gaining weight, and an obesity researcher snapped, “Well, you wouldn’t do well in a famine, would you?” Point taken; those with fast metabolisms die first when food is scarce. A bit of extra weight provides reserves not just in times of starvation, but also during some illnesses, like cancer and AIDS, which can cause people to lose weight and become weaker.
Again, we’re not saying weight doesn’t matter — but fitness and nutrition may be far more important to your health than the number on your scale. If you’re exercising, and eating healthful foods, don’t worry about a few extra pounds.
1. Flegal KM, Kit BK, Orpana H et al., “Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index Categories: A Systematic Review and Meta-analysis,” JAMA 2013; 309(1): 71-82. doi:10.1001/jama.2012.113905.
2. NHLBI Obesity Education Initiative Expert Panel on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report, Bethesda MD: National Heart, Lung, and Blood Institute, 1998. NIH Publication No 98-4083. Available online at:http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm.
3. McPartland JM, “Obesity, the Endocannabinoid System, and Bias Arising from Pharmaceutical Sponsorship,” PLoS One 2009; 4(3): e5092. doi:10.1371/journal.pone.0005092.