Interactions of obesity associated behaviours, BMI, age, sex, and FTO genotype

Obesity is a complicated condition which occurs due to interactions between many contributing physiological, psychological and genetic factors. Age, sex and body mass index (BMI) are also important in the interaction with obesity-related factors leading to a rise in this epidemic. Knowledge about the interactions that happen between these factors provides a basis for the development of body mass-reducing interventions for people with obesity. Eating behaviours affect caloric intake and are implicated in the development of obesity. Three types of eating behaviours namely; 1) cognitive restraint, 2) emotional eating and 3) uncontrolled eating have been studied for associations with obesity in various populations. Food cravings refer to an irresistible urge to eat a specific type of food which has been implied to contribute to a loss of control over eating. The experience of food cravings is related to higher BMI and obesity. Motivation to exercise is also an important factor that influences people´s eating habits as shown in previous studies. A taxonomy where motivation is organised in the form of a continuum that covers the different degrees of self-determination of behaviour, from the non-self-determined, to the self-determined, established three types of motivation (amotivation, extrinsic motivation and intrinsic motivation) and a series of behavioural regulation stages (amotivation, external regulation, introjected regulation, identified regulation and intrinsic regulation). Problems with emotional regulation may contribute to the development and maintenance of abnormal eating behaviour. Alexithymia is defined as an inability to describe and/or recognise one's own emotions and is considered a common feature in eating disorders. Alexithymia is likely to be associated with problems in modulating affect and with difficulties in the interpersonal and social realm. The programme of research as part of this PhD was conducted on 424 volunteers from Sheffield Hallam University students and staff, and there were 183 participants of weight-loss interventions. Eating behaviours were measured using the revised Three-Factor Eating Questionnaire (TFEQ-R18); food cravings were measured by the food cravings inventory (FCI), motivation for exercise using the Behavioural Regulation in Exercise Questionnaire-2 (BREQ-2) and alexithymia was measured by The Toronto Alexithymia Scale (TAS 20). DNA samples were genotyped using the TaqMan method for the rs9939609 polymorphism in the obesity-associated gene FTO. Questionnaire data were analysed for associations between the TFEQ-R18 and FCI, BREQ2 and TAS20 subscales for the whole study group, and the group divided by sex, genotype, age (≤ 25 years vs > 25 years) and BMI (<30kg/m² and ≥30kg/m²). Regression and mediation analyses were used to explore the relationships between BMI, eating behaviours, food cravings, motivation to exercise and alexithymia. The key findings from each of the experimental chapters in this thesis is 1) Increased cognitive restraint was associated with decreased food craving scores in the ≤ 25 years group; in this group the association between BMI and reduced food cravings was mediated by cognitive restraint indicating that in this age group individuals use cognitive restraint to control their food cravings. 2) Motivation to exercise interacts with eating behaviours and high motivation to exercise is associated with low BMI, people with obesity were less motivated than non-obese, emotional eating is the mediator between external regulations and high BMI. 3) There is a positive relationship between BMI and alexithymia in females, but in contrast there is an inverse relationship in men. The relationship between BMI and alexithymia was stronger in the AA+ AT genotype group than TT genotype. Uncontrolled eating and emotional eating mediate the effect of alexithymia on BMI and this is different between males and females and between genotype groups; particularly in females with the risk genotype, alexithymia were associated with high uncontrolled eating and emotional eating and so higher BMI. Males and/or people with the TT genotype are less at risk of this influence of alexithymia on BMI. These findings will help in the treatment of obesity by informing personal intervention programmes for each person according to his or her situation.

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