Obesity costs the global economy around US$2 trillion a year and risk factors linked to poor diet contribute to more disease than unsafe sex, alcohol, drugs, and tobacco use combined. Weight loss can reduce health problems but it is well known that maintaining a reduced body weight is very challenging for some people.

At present we know very little about why some people are able to lose weight and keep it off while others find it difficult. If we can better identify the factors that enable some people to keep weight off then this will help develop interventions to aid others in maintaining weight loss.

To find out more about the characteristics of successful weight loss maintainers, researchers from the School of Psychology at the University of Birmingham and the University of Amsterdam have studied how people respond to palatable foods. This is because how we respond to palatable food temptations is likely to be related to successful control of food intake and weight loss maintenance.

Community volunteers were given a freshly prepared pizza and were asked to smell the pizza before eating as much as they liked. The researchers assessed how much the volunteers responded to the pizza smell in terms of the amount they salivated and how much their heart rate increased as a measure of physiological arousal. The responses of three weight groups were compared: successful weight-loss maintainers; individuals with current obesity and never-overweight lean individuals. The physiological response of successful weight-loss maintainers decreased, when they were provided with the pizza, whereas participants with obesity had a heightened physiological response and the lean individuals were unresponsive.

Differences in the physiological response to smelling and tasting a pizza are dependent on previous experiences of eating pizza. If we get a lot of pleasure or reward from eating pizza then we react strongly when we just see or smell pizza and we may be more likely to overconsume. To test whether the groups differed in their ability to learn about food rewards, the researchers asked participants to play a game in which they had to learn an association between a neutral picture and the likelihood of winning (or avoid losing) jelly beans that they could take away with them afterwards. The weight loss maintainer’s ability to learn the task was more dependent on avoiding losses than gaining “wins” suggesting they are less sensitive to food rewards than the other groups. Importantly, all groups showed very similar motivation in another version of the game in which they could receive money “wins” and avoid money “losses”. These findings suggest that food has less value for weight loss maintainers, which was reflected in their lower physiological reactivity to pizza as well as their learning about food rewards.

These findings add to knowledge about the factors that might predict successful weight loss maintenance but it will be important to conduct longitudinal research to determine whether reduced physiological response to palatable food is predictive of successful restriction of food intake or whether successful restriction changes responses to food. Only if we know more about the factors that contribute to successful weight loss maintenance will it be possible to design more effective ways to help people achieve healthier weight outcomes. Obesity-related research and health care have been focused on weight loss but there is a clear need for evidence-based approaches in order to maintain weight loss.

Leonie Balter
PhD Psychology Joint Amsterdam
School of Psychology