Do Fat People Live Longer? How Weight Affects Longevity

This may be the first time you hear that carrying around some extra weight may actually be good for your health.

While the connection between health, obesity, and weight has been the subject of ongoing debate (and will likely continue to be so) for a long time, one study found that there may just be a positive relationship between body fat and life expectancy.

Since 2003, researchers at the UC Irvine Institute for Memory Impairments and Neurological Disorders (UCI MIND) have been conducting a still-ongoing study — referred to as "The 90+ Study" — to gain greater insight into the role of lifestyle, diet, health, and other factors play in longevity.

While their stated goal was understanding what allows people to live to age 90 and beyond, their findings uncovered surprising information about longevity among fat people.

And their findings deliver insight into why fat people live longer.

RELATED: The Unexpected Way Birth Order Affects Your Weight, According To Science

Over the course of their in-depth look at the lifespan of more than 1,600 people belonging to the generation the team calls "the oldest old," one particularly surprising finding emerged.

People who were overweight in their 70s lived longer than people who were normal or underweight.

This is good news considering that the most recent statistics show an estimated 1 in 3 adults in the U.S. are considered to be overweight.

But with that being said, there is also no doubt that extreme obesity carries an increased risk of illness and even death.

Do skinny people live longer? According to a study from the Lancet Diabetes and Endocrinology, life expectancy is shortened by 4.3 years for obese men and 3.5 years for obese women. However, life expectancy was also shortened for underweight men and women, with 4.3 years less for underweight men and 4.5 years less for underweight women.

If a person has over 31 percent body fat, the person is not considered healthy. It's normal to have a bit of fat or "chubbiness," but when your BMI is over 30, you are considered obese, which is a big difference from being overweight.

Do overweight people live longer?

The findings from "The 90+ Study" align with a 2013 study out of the Journal And Medical Medical Association, which found that being slightly overweight lowers your risk of death.

The researchers focused on body mass index and on death rates, and looked at nearly 300 studies around the world. The studies included almost 3 million people and over 270,000 deaths. The people in the overweight BMI category lived longer than those in the normal weight category, with a 6 percent lower risk of dying. 

Other studies have found that older people over the age of 70 who packed on extra pounds have lived longer than those who don't because, according to lead researcher Leon Flicker, PhD, of the University of Western Australia, your body mass index (BMI) weight isn't useful after age 70.

Authors of "The 90+ Study" used the following terminology in keeping with that of the National Heart, Lung, and Blood Institute:

Underweight: BMI of less than 18.5

Normal weight: BMI of 18.5 to less than 25

Overweight: BMI of 25 to less than 30

Grade 1 obesity BMI of 30 to less than 35

Grade 2 obesity: BMI of 35 to less than 40

Grade 3 obesity: BMI of 40 or greater

"Relative to normal weight," they explained, "both obesity (all grades) and grades 2 and 3 obesity were associated with significantly higher all-cause mortality. Grade 1 obesity overall was not associated with higher mortality, and overweight was associated with significantly lower all-cause mortality."

RELATED: The Psychological Link Between Your Emotions & Likelihood Of Becoming Obese

In layman's terms, this means that people in the two highest categories of obesity have the shortest life expectancy of all, those who are "overweight" have the longest life expectancy of all, and people who are just slightly obese are no more likely to have a shorter life span than anyone else.