The influence of anticipated meal timings on portion size decisions and interactions between meal timings, BMI, and delay discounting

Abstract

Obesity is a global epidemic. Understanding drivers of food intake is critical to developing successful interventions. However, the current literature has neglected to consider the interaction between meal planning and future thinking in portion size decisions. For the first time, this thesis explores how anticipated meal timings influence portion selection. Novel methods manipulated the length and certainty of an inter-meal interval (IMI) and measured computerised and real portion size selection. Findings showed that information about the length of an IMI influences portion size decisions, and that individuals with a high BMI are less sensitive to information about the length and certainty of an IMI.

There is poor understanding of how future-orientated thinking influences decision making in this context. The studies compared performance on previously unrelated tasks; portion size selection in response to IMIs and monetary delay discounting. Results suggest that monetary discounting is associated with portion selection in response to uncertain, but not certain IMIs. An experiment assessing the effects of fasting on monetary and dietary discounting found that hunger had opposing effects on discounting of food and money; increasing dietary and decreasing monetary delay discounting. The thesis concludes that delay discounting is commodity specific, and therefore monetary tasks are not an adequate proxy for future-orientated eating behaviours.

The thesis also evaluated guidelines that regular meal timings promote weight loss. In studies assessing the relationship between BMI and chaotic eating (eating at irregular timings) no relationship was found, thus failing to support dietary recommendations. The thesis highlights that future thinking about meal timings effects portion size and is related to BMI. Nevertheless, current understanding of how future meal planning interacts with portion size, delay discounting and BMI is limited. Further research is necessary to establish how these separate aspects interact to promote, or protect against, obesity.

Date of Award	23 Jan 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jeff Brunstrom (Supervisor)