Do you have an overweight personality?

By Deborah Kotz, Globe Staff

Is your body weight a sign of your personality? The politically incorrect answer that comes from a new study is yes. Public health experts have been blaming societal structure -- not willpower -- for our nation’s growing waistline that has left two-thirds of Americans overweight: junk food is too cheap; walking paths too inaccessible; driving too easy. But researchers from the National Institute of Aging have now found that personality plays a hefty role too in terms of weight changes over the decades.

They performed regular body mass index measurements and personality questionnaires in nearly 1,800 participants who volunteered to take part in the ongoing Baltimore Longitudinal Study of Aging and found that two traits -- impulsivity and conscientiousness -- played the strongest role in determining mid-life weight gain. Those who scored the highest for impulsive, disorganized behaviors gained 22 pounds more, on average, over two decades compared to those who scored the lowest for these behaviors, according to a July study published in the Journal of Personality and Social Psychology.

That’s not a huge surprise given that those who act on impulse will probably down more doughnuts, cheeseburgers, and margaritas over the course of a lifetime, and be more likely to skip the gym, than those who exert self discipline and control. “Those who are more conscientious tend to eat and exercise on a more regular schedule and are less likely to binge eat or drink -- all things that contribute to a more stable weight,” said study author Angelina Sutin, a psychologist at the National Institute on Aging.

Interestingly, though, the researchers also found that highly competitive, antagonistic personalities also tended to gain more weight over time. Sutin speculated that this might be due to these individuals exerting a stronger stress response in any given situation and that the high stress responses leads to overeating.

Even yo-yo dieters may have specific personality traits: Those who scored high on the neuroticism scale -- always worried, say, about what others think of them -- had a greater likelihood of experiencing repeated cycles of weight gain and loss over the decades, which Sutin said she couldn’t explain.

What the study didn’t find was a shift in personality traits that paralleled large weight changes. “We were pretty surprised by that,” said Sutin. After all, obesity has been linked to depression and social ostracism, while diet companies love to tout the confidence-building payoffs that come with reaching your goal weight.

If our personalities are fixed, does this mean we’re doomed to be fat if we’re more impulsive than conscientious?

“While personality tends to be resistant to change,” said Sutin, “we can change how we express behaviors that are related to weight gain.” Impulsive people can remind themselves to be more organized, scheduling meals at set times so they don’t binge, setting a smart phone reminder to pack their gym bag, and making a grocery store list so they don’t forget the fresh garlic, salmon, and berries.

And while Sutin pointed out that the study underscores individual differences among us when it comes to mid-life weight gain, it doesn’t “in any way exonerate society” for failing to adequately address the current obesity epidemic.