There is a tendency to look at people who have put on weight and assume that there is something about their personality that made them gain weight. We rarely contemplate the opposite possibility, though. Perhaps behaviors that lead people to gain weight actually lead to changes in people’s personality over time.

This possibility was explored in a fascinating paper by Angelina Suttin and seven co-authors in the July, 2013 issue of Psychological Science. These authors examined data from about 2000 people taken from two longitudinal studies. The adults in these studies were generally in their 40s and 50s at the time of the first measurement. The individuals in these studies took a basic personality inventory and also had their height and weight measured (in one study) or they self-reported their weight (in the other). The measurements for each individual were taken 8-10 years apart.

The researchers analyzed the data to see whether significant weight gain (a gain of more than 10 pounds) and significant weight loss (a loss of more than 10 pounds) influenced measures of personality. Weight loss had no reliable effect on the measures of personality. However, weight gain had two relationships to personality.

Participants who gained more than 10 pounds were just as impulsive as those who did not at the baseline measure, but were significantly more impulsive in the follow-up test than those who did not gain weight. Surprisingly, those who gained weight also increased in how likely they were to deliberate about decisions compared to those who did not gain weight.

This pair of findings is interesting for a number of reasons. First, it suggests that repeated behaviors that lead to bodily changes can ultimately influence personality characteristics as well. Giving in and eating too much repeatedly over a 10-year period can lead people to become more impulsive overall.

Second, the combination of results for impulsiveness and deliberation is interesting. You might think that people who are impulsive do not think about their actions and the consequences of their actions. In this case, though, people are both more impulsive and more deliberative. That means that they likely understand the consequences of their impulsiveness, but they cannot stop themselves from acting.

These data suggest that it might be useful to take a different approach to weight loss, particularly with older adults. Often, we provide a lot of information about healthy eating and weight loss. The assumption is that if more people understood why their eating habits are leading to weight gain and potential bad health, they would change the way they eat.

These data suggest that information alone is unlikely to help. The people in this study are able to think about their acitons, they simply don’t change their behavior in the face of temptation. That suggests that we need to help people to change their environment to make the behaviors they want to perform easier to do and the behaviors they want to avoid harder to do. In addition, it suggests that people need to engage with family and friends to save them from temptation. Ultimately, when you are likely to be impulsive, the people around you can be a great source of strength.

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