Across the globe, people of all walks of life are making similar New Year’s resolutions: Join a gym; lose some weight; fit into those skinny jeans — in other words, get healthier. But 2013 may be the time for rethinking what “healthy” means in the first place. New research suggests being slightly overweight is actually associated with a lower risk of dying. So is it time for a post-holiday cookie binge?

What’s the Deal?

Researchers led by Dr. Katherine M. Flegel of the Centers for Disease Control and Prevention analyzed the link between Body Mass Index (BMI) and mortality in almost 100 studies from the PubMed and EMBASE databases. Combined, the studies included more than three million adults, and all studies adjusted for age, sex, and smoking habits.

People with a BMI between 18.5 and 25 were considered normal weight; those with BMIs over 25 were labeled overweight; a BMI between 30 and 35 meant grade 1 obesity; and anything higher than that meant grade 2 or 3 obesity. The results found that a little pudge had a protective effect: The overweight folks had a six percent lower risk of death, while those in the grade 1 obesity category had a five percent lower risk of death. But in this case, moderation really proved to be key: Anyone with higher than moderate obesity (i.e. the grades 2 and 3 obesity categories) had a 29 percent increased risk of death.

The study authors can’t say for sure that a higher BMI directly causes a longer lifespan, but they suggest there may actually be cardiovascular benefits and other positive health effects to a little extra body fat and higher metabolic reserves (energy the body has available to utilize).

Why It Matters

This research isn’t the first to suggest that a slightly elevated BMI is associated with a lower risk of dying [1]. Similarly, studies find that being underweight actually increases mortality risk [2] [3] [4]. But there might be more at play than a simple connection between being overweight and having better health.

For one thing, the authors admit this particular study only looked at “all-cause mortality,” or death from any reason. There’s substantial evidence suggesting that being overweight or obese is a risk factor for diseases such as diabetes and cardiovascular disease [5] [6]. “All-cause” obviously includes diabetes and heart disease, but if the study authors had looked at the rates of death from just those two health issues among people with different BMIs, the results might theoretically have shown that overweight and obese people actually had an increased risk of death.

Is It Legit?

Sorta. It’s possible that BMI just isn’t a great predictor of mortality risk or even health in general. BMI doesn’t take into account some important aspects of health, including blood pressure, blood sugar, and cholesterol. Some experts also point out that BMI doesn't say anything about a person's muscle mass. Other body measurements, such as visceral (abdominal) fat or fat distribution and waist circumference or waist-to-height ratio may give a better picture of a person’s health [7]. People with larger waist circumferences and higher amounts of visceral fat, for example, usually exhibit risk factors for cardiovascular disease. Another, somewhat counterintuitive, idea is that overweight and obese patients are more likely to present health problems (such as diabetes) that require them to visit a doctor regularly, meaning whatever medical issues they have get treated.

So, for those whose resolutions had something to do with buying new running shoes or growing an affinity for brussels sprouts, keep at it. These results aren’t an incentive to let healthy habits fall by the wayside. Rather, this study serves as a call to continue studying the link between body composition and certain medical issues — and a reminder that our attitudes about what constitutes a “healthy” body might benefit from some expansion of their own.

Do you think someone’s BMI is a good indicator of his or her health status? Let us know in the comments below or tweet the author directly at @ShanaDLebowitz.