Obese and overweight less likely to consider next meal when making portion size decisions

University of Bristol researchers have found that people with obesity tend to ignore how long it will be until the next meal when choosing how much to eat. In a study designed see if people consider the time interval between two meals when selecting portion sizes, the researchers found that lean people generally do. However, obese people tend to discount that information. The findings will be presented this week at the 2017 Annual Meeting of the Society for the Study of Ingestive Behavior (SSIB), the leading scientific society for research into all aspects of eating and drinking behavior.

Obesity has previously been linked to differences in "delay discounting" - the tendency to treat something as less significant based on how far in the it will occur. Delay discounting is a facet of impulsivity, encouraging decisions in the moment that disregard future rewards or consequences. Typically psychologists study how discounting works in tasks using money. In this study, for the first time, the Bristol researchers assessed how people with discount information about future meal timings.

"Meal timings and future planning are an important area of research in obesity. These findings are exciting because they are the first to demonstrate that discounting operates in planning from one meal to the next and that people with obesity might not be factoring that in to their choices," said lead author Annie Zimmerman, a doctoral student at the University of Bristol. "Our results are consistent with the idea that overeating is promoted by feeling in the moment, disregarding future consequences of decisions. This novel finding might help to explain why being overweight is associated with irregular meal timings. Potentially there could be targeted interventions for obesity to promote future thinking in meal planning."

In the study, participants completed a series of computerized tasks, which included selecting lunch after being told how long after lunch the next meal would be (ranging up to 8 hours later). The researchers found that individuals with a high BMI were less influenced by information about the inter-meal interval when making portion size decisions. Additionally, participants completed a monetary delay discounting task. There was no interaction between the monetary delay discounting task and the inter-meal interval , although both independently predicted BMI. This suggests that these factors work in parallel, but tap into separate traits related to obesity.

"It is particularly interesting that monetary discounting was not related to sensitivity to future meal timings. The literature is beginning to differentiate between discounting of food and money - our findings are consistent with the idea that there temporal discounting works differently for different reward types. Our results highlight the need to distinguish between long-term monetary discounting and shorter-term discounting between meals. To fully understand the role of dietary discounting in eating behaviours and the links to obesity we need to develop a multifaceted model of discounting," explained Zimmerman.

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