People who gain weight through eating second helpings are completely aware of their actions, but they just can't resist the temptation.

According to a new study published in Psychological Science, people who have gained weight are more likely to give in to temptation, even though they are more thoughtful about their actions. Psychologist Angelina Sutin of the Florida State University College of Medicine and colleagues at the National Institute of Health (NIH) sought to understand how fluctuations in body weight relate to personality changes.

The researchers hypothesized that "those who gained weight would become more impulsive, undisciplined, and less thoughtful because high impulsiveness, low self-discipline and low deliberation have been associated with a higher body-mass index and weight gain."

The study consisted of two separate trials, NIH's Baltimore Longitudinal Study of Aging and the Baltimore Epidemiological Catchment Area study. They collected data on the personality traits and body weight of more than 1,900 people at two time points separated by almost a decade. In one study, participants' weights were measured 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.

The researchers found that those participants who showed at least a 10 percent increase in body weight also showed an increase in impulsiveness.

"If mind and body are intertwined, then if one changes the other should change too," Sutin said in a statement. "That's what our findings suggest."

What surprised the researchers was that those who gained weight also reported an increase in deliberation, and although deliberation increases for everyone with adulthood, the study suggests that weight gain could "amplify this normative age-related trend."

They speculate that the reason behind more deliberation could be that "a close other may be more likely to make an offhand comment about a second helping at dinner to someone in the midst of weight gain than someone whose weight is stable."

In short, thinking a little longer about how that extra serving will contribute to future weight gain won't necessarily translate to resisting the temptation.