To understand how fluctuations in body weight might relate to personality changes, psychological scientist Angelina Sutin of the Florida State University College of Medicine and colleagues at the National Institutes of Health (NIH) examined data from two large-scale longitudinal studies of Baltimore residents.
The studies, NIH's Baltimore Longitudinal Study of Aging (BLSA) and the Baltimore Epidemiologic Catchment Area (ECA) study, included more than 1,900 people in total, of all ages and socioeconomic levels.
Data about participants' personality traits and their body weight were collected at two time points separated by nearly a decade. In one study, a clinician measured participants' weight at the two time points; in the other study, the participants reported their weight at baseline and had it measured by a clinician at follow-up.
Sutin and colleagues found that participants who had at least a 10 percent increase in body weight showed an increase in impulsiveness - with a greater tendency to give in to temptations - compared to those whose weight was stable.
The data don't reveal whether increased impulsiveness was a cause or an effect of gaining weight, but they do suggest an intimate relationship between a person's physiology and his or her psychology.
In a surprising twist, people who gained weight also reported an increase in deliberation, with a greater tendency to think through their decisions. Deliberation tends to increase for everyone in adulthood, but the increase was almost double for participants who gained weight compared to those whose weight stayed the same.
"If mind and body are intertwined, then if one changes the other should change too. That's what our findings suggest," Sutin said.
Sutin and colleagues speculate that this increase in deliberation could be the result of negative feedback from family or friends - people are likely to think twice about grabbing a second slice of cake if they feel that everyone is watching them take it.
These findings suggest that even though people who gain weight are more conscious of their decision-making, they may still have difficulty resisting temptations.
The study was published in Psychological Science, a journal of the Association for Psychological Science.