Drivers of obesity?

: Characterising biopsychological and environmental factors associated with overeating

Abstract

The prevalence of obesity has increased globally over the past four decades, and one of the primary factors implicated is the increased availability of highly processed, inexpensive, energy-dense foods that offer palatability but little nutritional value. However, not all humans are obese, suggesting that the individual variation in several physiological, psychological, biological and social-economic factors play a role in moderating eating behaviour in response to palatable food cues. The purpose of this thesis is to investigate (a) how the increased availability of highly palatable energy-dense foods, served in large portions yet containing little nutritional value, impacts appetite and amounts eaten; (b) how the individual variation in psychological, physiological, biological and socio-economic characteristics increases the susceptibility to overeating these foods.

The first two studies investigated the appetite and eating behaviour responses to consuming foods containing high levels of fat and sugar (Chapter 3 and 4). In a sample of twenty-five adults, the addition of sweetness to a high-fat food significantly enhanced the palatability and desire to eat on initial tasting. During the early stages of the meal, sweetness sustained feelings of hunger and the motivation to eat. These responses were associated with a higher intake of food (Chapter 3).In a second study, in ten participants, sweetness sustained prandial acyl-ghrelin levels, but these responses were not associated with increased food intake (Chapter 4).

The third study investigated how the individual variation in lifestyle factors (level of physical activity), dietary protein requirements and physiological characteristics influenced the appetite and eating behavioural responses to low protein intake (Chapter 5). Level of physical activity did not influence the response to a low protein meal as marginal differences were observed between the active (n = iii 9), moderately active (n = 9), and sedentary group (n = 8). However, across the group it was found that body composition and resting metabolic rate was strongly associated with energy and protein intake.

The fourth study investigated the biological, psychological, anthropometric and socio-economic factors associated with obesity-related eating behaviours and attitudes toward food in a large community-based sample (n = 560, 240 men, 320 women). In this sample, overweight individuals or individuals with obesity were more likely to have the at-risk AA/AT FTO allele and be of lower socioeconomic status; in addition, they showed a greater motivation to eat energy-dense foods and reported eating these foods more often. Furthermore, when viewing images of fixed portions of food, overweight and obese individuals reported lower anticipated satiation for energy-dense foods (Chapter 6).

The final study investigated the relationship between estimated portion size chosen for lunch and obesity in a large community-based sample (n = 555, 235 men, 306 women). The maximum food portion size for five foods was predicted by resting metabolic rate, body fat (waist-to-height ratio), age and sex. Body mass index and fat mass did not significantly predict portion size. Individuals with a higher resting metabolic rate chose larger food portions, while a higher waist-to-height ratio predicted smaller portion sizes. Across the sample, the maximum portion size of high energy-dense foods chosen provided more energy than the energy provided by portions of low energy-dense foods (Chapter 7).

Taken together, these results suggest a Western-style diet of energy-dense foods, rich in fat and sugar, influences appetite and eating behaviour. These foods heighten the sensory experience and reward response when eating, consequently encouraging a higher food intake. The individual variation in protein need and level iv of physical activity may modify the response to a low protein diet or meal; however further research is needed to investigate this research question. This thesis observed the individual variation in body composition and metabolic rate may direct food intake, macronutrient balance, and decisions about food portion size. The individual variation in restrained eating, weight status and inheritable traits may also increase the susceptibility to palatable food cues, meaning that these individuals are at risk of overeating. Individuals of lower socioeconomic status may also be vulnerable to overeating energy-dense foods as they demonstrate a heightened reward response and preference for high energy-dense foods yet find these foods to be less satisfying. These findings provide an informative insight into the factors that influence overeating and the development of obesity. Importantly, these insights should advance the development of research in this area.

Date of Award	2 Oct 2021
Original language	English
Awarding Institution	University of Roehampton
Supervisor	Leigh Gibson (Director of Studies) & Lewis Halsey (Co-Supervisor)