Being obese is dangerous for your health. And so is being overweight, right? Well, yes. Or no. Or maybe. Or, it kind of depends. The answer is complicated.
Recent research looked at almost 100 studies with about 3 million adults. The researchers found, unsurprisingly, that obesity was linked to a shorter life span.
But they also found that being overweight very slightly was linked to a longer life span. That doesn't seem to make sense. Is being overweight good for you?
Not necessarily. It's important to understand what the study looked at and different reasons why being overweight was linked to a longer life span.
"Talk to your doctor about maintaining a healthy weight."
The study, led by Katherine M. Flegal, PhD, from the National Center for Health Statistics at the Centers for Disease Control and Prevention, analyzed 97 studies that included a total of about 2.88 million people.
The studies compared the body mass index (BMI) of people and their risk of death for any reason. BMI is a ratio of a person's height to their weight. It is used to determine whether they are underweight, a healthy weight, overweight, obese or morbidly obese.
Over 270,000 deaths were recorded in the studies analyzed. The studies came primarily from North America or Europe (78 total), and the rest were from various other places, such as Japan, China and Brazil.
The researchers compared the risk of death among overweight and obese individuals to those with a normal weight.
They found that those who were obese, which means their BMI was at 30 or higher, had an 18 percent higher risk of death compared to those of a normal weight. This was unsurprising because obesity is linked to a range of diseases, such as cardiovascular disease and diabetes.
Those who were the most obese, with BMIs over 35, had 29 percent higher risk of death compared to those with a healthy weight.
Oddly, those who were moderately obese (BMI from 30 to 34) had a 5 percent lower risk of death. And those who were overweight (BMI from 25 to 29) had a 6 percent lower risk of death than those in the normal weight range.
What's Going On Then?
So what's going on here? Should you gain weight to live longer?
Not necessarily. First of all, the difference between risk of death among individuals with a normal weight and those who are overweight or slightly obese is very, very small. It did not appear due to statistical chance, but it is not major either.
In addition, the range of normal weight (BMI from 18.5 to 25) may include people who are underweight. Many underweight individuals may be more likely to have other health conditions. Or, despite the studies that tried to adjust their findings for other diseases, underweight individuals may have illnesses contributing to their lower weight, such as cancer.
Further, the strong links between being overweight or obese and various diseases have not changed. Even if those who are overweight or moderately obese appear on paper to be living longer, that doesn't mean they are living disease-free or healthily.
In fact, some of the studies included in the analysis only followed people for five or ten years. The individuals in the study may still have been alive at the end of that five-year or ten-year study, but they may have had chronic diseases like cardiovascular disease or diabetes.
In addition, past studies have shown that being overweight puts you at risk for becoming obese, and being obese puts you at risk for becoming morbidly obese.
In one sense, gaining weight may be like a "gateway" to continuing to gain weight. If an individual continues to gain weight, it is not difficult to cross into obese territory, where your risk of disease and death go up considerably.
Overweight Individuals May Sometimes Get Protective Benefits
Another possibility, noted by the researchers, is that those who are overweight or moderately obese may be getting medical help sooner, or their doctors may be paying more attention to possible problems because they are overweight. If they are receiving quality health care, then their risk of death will drop.
Meanwhile, if those in the normal weight range are not all receiving as much or as careful regular health care, they may develop conditions that are not caught as soon. This may not necessarily explain the entire difference in risks of death, but it is a possibility.
Another distinction might be related to where the body fat is on the overweight and moderately obese individuals, which this study did not look at. Belly fat is dangerous, according to much research.
Body fat in other parts of the body may not be as dangerous or may even offer protective benefits, such as body fat in the hips helping to cushion the fall in older individuals who may then sustain less injury.
In an editorial accompanying the study, Steven B. Heymsfield, MD, and William T. Cefalu, MD, note that some diseases also have a better outcome if the individual has extra fat reserves.
“The presence of a wasting disease, heart disease, diabetes, renal dialysis or older age are all associated with an inverse relationship between BMI and mortality rate," they wrote. This means there is some evidence that individuals with these diseases appear to do better when they have extra weight.
So What Does It All Mean for Me?
BMI is not a perfect measure of what's healthy. Muscle weighs more than fat, so an extremely muscular (and healthy) individual may appear to have a higher BMI than normal when they actually have less body fat. In fact, it's possible that a tiny amount of the difference in death risk in this study was related to very muscular individuals whose BMI put them in the overweight or moderately obese range even if they were healthy.
The bottom line is that being overweight according to your BMI may or may not contribute to your own personal risk of disease or an early death. Being morbidly obese by BMI standards definitely contributes to your risk for disease and early death, however.
BMI is a rough calculation of whether you are in the healthy range for your weight. If your BMI puts you in the category of overweight or moderately obese, it is best to discuss your personal health with your doctor to determine whether you should lose weight and what the healthiest way to do so is.
“Not all patients classified as being overweight or having grade 1 obesity [BMI of 30 to 34], particularly those with chronic diseases, can be assumed to require weight loss treatment," Dr. Heymsfield and Dr. Cefalu wrote. "Establishing BMI is only the first step toward a more comprehensive risk evaluation.”
The study was published January 2 in JAMA. No external funding was used for the study, and the authors declared no conflicts of interest.