Extroverts tend to be overweight, while anxious types are more likely to be thin. Japanese researchers surveyed more than 30,000 people aged between 40 and 64 about their height and weight, and subjected them a personality test. The results showed that outgoing people were far more likely to have a body mass index (BMI) of more than 25 (defined as overweight). People with the most anxious personalities were twice as likely as the least anxious to be underweight, (BMI under 18.5). (Personality and body mass index: a cross-sectional analysis from the Miyagi Cohort Study. J Psychosom Res. 2008 Jan;64(1):71-80).