People with a passive personality run a higher risk of obesity and related diseases such as type 2 diabetes, biologist Gretha Boersma has discovered. But there is also good news: ‘They can often be easier to treat than proactive personalities, who may develop obesity less quickly, but are less open to “life-style” interventions.’ Boersma will be awarded a PhD by the University of Groningen on 7 March 2011.
Some people quickly develop obesity and type 2 diabetes. Others don’t, despite being in comparable situations. These individual differences make treating obesity-related diseases very difficult.
Boersma researched the cause of the differences using an animal model with two different personality types: rats with a passive coping style and rats with a proactive way of dealing with stress. Boersma: ‘A passive personality avoids stress, is usually an introvert, has low aggression levels and is not impulsive. Proactive personalities are extravert, impulsive, rather more aggressive and have a strong need to follow routines. You see these types in both animals and people.’
In a situation with standard food and a standard cage, it quickly turned out that passive animals developed insulin resistance more quickly – the first step in the direction of type 2 diabetes. However, when the animals were given access to an exercise wheel the passive animals suddenly demonstrated increased physical activity. This was particularly the case if the fat content of their diet was increased too. Boersma: ‘The passive animals began to compensate for their diet by taking more exercise in the exercise wheel. The proactive animals stuck to their old routine. They exercised just as much as with the normal diet.’
This latter situation is comparable to that of people, according to Boersma. ‘Many people take very little exercise during their (sedentary) work. And we also have access to food throughout the day. In such situations, passive personalities develop weight problems and the related diseases relatively quickly.
The fact that passive personalities are more susceptible to interventions has also been revealed by a pilot study where people with obesity followed a training programme. Boersma: ‘Although the training had a positive effect for both personality types, people with a passive personality were more active during the training sessions. Unfortunately they tended to compensate by taking less exercise on the “rest days”. That did not happen to the proactive personalities. Married to their routines, they were just as active on the other days as they had been before their participation in the training programme.’
‘But when the “passive” people were made aware of their compensatory behaviour, they turned out to be able to increase their activity and thus achieved better results,’ says Boersma. Just as in the rat study, passive personalities turn out to be more sensitive to influences from their environment than proactive personalities. This has important consequences for the ways of treating type 2 diabetes, thinks Boersma. ‘Take the interaction between the patient’s living environment and his or her personality type into account and choose a treatment method that matches.’
In practice this step is easy to take, according to Boersma. ‘The personality type is easy to establish, and then you have a more objective picture of the treatment needed. For example, you could say that you’d have to draw up a daily training schedule as part of the treatment of a more passive person. That would prevent them compensating. More proactive types would benefit more from sports where they would be in competition with others.’
Gretha J. Boersma (Drachten, 1982) studied Biology at the University of Groningen. Her PhD supervisors were Prof. Anton J.W. Scheurink and Prof. Gertjan van Dijk. Her thesis is entitled Personality and the pathophysiology of energy metabolism. In December, Boersma was awarded a Rubicon grant by NWO and will be starting as a postdoc at the Department of Behavioral Neurosciences at Johns Hopkins University in Baltimore, US, on 1 April.
More information: Gretha Boersma, tel. 050-363 2345, e-mail: g.j.boersma rug.nl
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