Successful weight loss maintainers have different behavioural and physiological responses to food than obese people and lean people, according to new research by the University of Birmingham and the University of Amsterdam presented at the European Congress on Obesity in Vienna.

The University of Birmingham reports the findings indicate a reduced physiological response to highly palatable foods such as pizza, and reduced sensitivity to winning foods, may help explain why some people are able to successfully lose weight in the long-term.

Current levels of obesity cost the global economy around $2 trillion a year, and risk factors linked to poor diet contribute to more disease than unsafe sex, alcohol, drugs, and tobacco use combined. There has been much research into how food environment and neurobiology can lead to overeating. For example, highly palatable foods such as pizza and chocolate trigger signals in the brain that give a feeling of pleasure and reward. These cravings contribute to overeating. But little is known if these responses to food cues support weight loss maintenance.

In the study Leonie Balter, from the University of Birmingham’s School of Psychology, and her colleagues looked at saliva production and heart rate following exposure to pizza in different weight groups with an average age of 29.5.

The team, from Suzanne Higgs’ Eating Behaviour Research Group, compared the responses of twenty successful weight loss maintainers who previously had obesity, twenty five people with current obesity, and twenty lean people who had never been overweight.

They found obese people had a heightened salivation and heart rate response. In contrast, the salivation and heart rate of successful weight loss maintainers decreased following presentation of the pizza, while lean people were unresponsive.

Participants also completed cognitive tasks to gauge their motivation to gain and avoid losing food and monetary rewards in a computerised task. Participants had to figure out whether a neutral symbol was associated with winning jelly beans, losing jelly beans, winning money or losing money. The ability of lean and obese people to learn the task was affected by losing and winning food equally, but the weight loss maintainers performance was less affected by food wins and more affected by food losses. Importantly, the three groups did not differ in their ability to learn the task in general as there was no difference in learning the task using monetary reward or losses.

The researchers conclude “Our findings reveal a marked difference in physiological reactivity to food depending on weight-loss history. The results suggest that explicit food rewards have less value for weight loss maintainers. Further longitudinal research is needed to determine whether reduced physiological response to palatable (high calorie) food and sensitivity to food rewards may be predictive of individuals that can successfully restrict food intake.”

This is an observational study, so no firm conclusions can be drawn about cause and effect and the authors point to several limitations, such as the current study having a small sample size. The results must therefore be replicated in a larger group of people.