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Gestational diabetes mellitus (GDM) is a type of diabetes which develops, or is first recognised during pregnancy. GDM increases the risk of medical complications during pregnancy, and its consequences extend to later in life, as both women and their children are at high risk of developing cardio-metabolic disease. Obesity and excessive gestational weight gain (GWG) are modifiable risk factors for GDM development. Therefore, the research in this thesis aimed to develop and evaluate dietary interventions to help prevent GDM. I initially explored the full burden of the disease using data from a big UK cohort. I found that women with GDM are at high risk of premature death. GDM increases the risk of subsequently developing cardiovascular disease (CVD) risk factors (diabetes, hypertension, dyslipidaemia), and increases the risk of incident CVD by 50% compared to no GDM. There was no evidence that the CVD risk factors explained the association of GDM with CVD, suggesting that all women with GDM are at increased risk of cardio-metabolic disease post-partum, and should be monitored. I then developed a dietary intervention of moderate total carbohydrate reduction, suitable for use in pregnancy, to help prevent GDM (RECORD). It combined a 30-minute dietary behavioural consultation, with structured written materials, brief telephone support throught pregnancy, and weekly self-weighing. In designing the behavioural component, I sought ways to increase motivation and adherence. I thought about using Motivational Interviewing (MI), a popular counselling style in behavioural weight management programmes (BWMPs). Due to increased training and time required for its delivery, I conducted a systematic review and meta-analysis to explore MI's independent effectiveness over other behavioural approaches in BWMPs for weight loss or maintenance, but found that it only leads to a small short-term weight benefit (-1 kg), and only when compared to no/minimal interventions, which makes it not a worthwile addition to weight management programmes with standard behavioural support. In a feasibility trial, I tested if it is possible to deliver the RECORD intervention alongside routine antenatal appointments, and how successful women with obesity would be in following it from early or mid-pregnancy until delivery. The trial's retention rate was excellent (96%), but recruitment was difficult. Adherence was highly variable, and on average, the reduction in total carbohydrate intake in women receiving the intervention was small (-19.5 g/day and -24.6 g/day absolute and adjusted changes from baseline), which limits the likelihood of achieving the desired goal to prevent GDM. I observed potentially favourable effects of the intervention on blood glucose, GWG, and blood pressure, but the trial was not powered to detect differences in these outcomes. In qualitative interviews, participants praised the intervention for its structure and simplicity, and generally found it acceptable, but a sub-sample reported barriers to adherence, such as competing priorities, and emotional relationship with food. Combining qualitative and quantitative data from this research, I identified opportunities for refinement of the intervention, recruitment strategy, and for routine practice, which could be explored in the future.

Reducing dietary salt intake plays an important role in the prevention and management of hypertension, yet the evidence for effective and scalable individual-level interventions is scarce. In this research I aimed to fill this gap by developing and testing an intervention to reduce salt intake in people with hypertension. Firstly, I investigated the impact of offering shoppers lower-salt alternatives when grocery shopping, in a randomised controlled trial using a simulated online supermarket platform. I found that shoppers were willing to swap to lower-salt alternatives, and that offering a wide range of products with greater reductions in salt (>20% less) significantly reduced the salt content of their shopping basket compared with offering alternatives which were more similar in nature and salt content (-0.09 g/100g, 95% C.I. -0.10 to -0.07 p<0.001). Secondary analysis showed that participants who had previously received advice to reduce their salt intake accepted more lower-salt swaps than those who had not. I then developed a primary care-led intervention, using a theoretical behaviour change framework, to motivate and support people with hypertension to reduce their salt intake, including an app to help them choose lower-salt food when grocery shopping. A feasibility randomised controlled trial showed that the intervention ('SaltSwap') could be delivered in routine primary care settings (intervention fidelity 81% and high acceptability among healthcare professionals), it successfully engaged individuals with high blood pressure (the intervention session was attended by all participants randomised to the intervention group and the SaltSwap app was used by 87% of intervention participants in the first month and in 75% of shopping trips overall) and encouraged participants to swap to lower-salt alternatives for foods which typically contribute most to salt intake. An in-depth qualitative study demonstrated that SaltSwap improved participants' knowledge and motivation to reduce salt intake, and individuals engaged with the SaltSwap app in a meaningful way. Together these results suggest that offering shoppers lower-salt alternatives is a promising approach to reducing salt intake among people with hypertension and a future large-scale trial to test the effectiveness of the SaltSwap intervention for reducing blood pressure is warranted.

Introduction: A poor diet is one of the leading causes of morbidity and premature mortality around the world. National and international policymakers recognise that changing the food supply is a crucial part in changing the diets of a population, yet there are few established methods to monitor the actions of food manufacturers and retailers. Aim: The overarching aim of this thesis was to develop and apply a new method pairing food sales data and nutrition composition data to allow the nature of the food supply to be quantified and monitored over time. Method: A systematic review identified potential sources of food sales data. A cross comparison data study, led to the selection of Euromonitor as the most appropriate source for food sales data with nutrition composition data collected from supermarket websites by commercial company Brand View. The sales data and nutrition information were paired based on product name, brand name and category. This unique method was then applied in two ways: first, by analysing the changes in the sugar content of selected food and drinks in the UK between 2015 and 2018 in the context of the UK Government's 20% sugar reduction targets and soft drinks industry levy (SDIL); and second by applying a nutrient profiling model to the top 10 UK companies' product portfolios, to develop a benchmarking tool based on the healthiness of companies' products. Results: Analysis showed that the sales-weighted mean sugar content of soft drinks fell by 34% between 2015 and 2018, from 4.4g/100ml to 2.9g/100ml. The total volume of sugars 2 sold from soft drinks decreased by 30%, from 15.5g per capita per day to 10.8g, a reduction of 4.7g. There was a much smaller decrease in the mean sugar content or sugar sales from food products included in the sugar reduction strategy. The total volume sales of sugar from the included categories fell by 8%, equating to 1.7g per capita per day with marked differences across food categories. However, there has been no significant change between 2015 and 2018 in the overall nutrient profiling score for the top 10 food and drink companies in the UK. In 2018, the sales-weighted mean score of all food and drinks was 65, below the score of 70 which can be considered 'healthy'. No individual company had an overall score of above 70. There was little change in the number of individual products classified as healthy, although the proportion of total sales classified as healthy increased from 38% to 46%. Discussion: This thesis provides novel insights into how companies have responded to Government public health policies, including the sugar reduction programme. A new method has been developed in this thesis that has the potential to be used continually to monitor the nutritional composition of the food supply, to evaluate which companies are making efforts to improve public health nutrition and to monitor the pace of change.

Producing meat generally leads to greater greenhouse gas emissions, deforestation, water use and pollution, and biodiversity loss compared to producing plant-based foods. While there are many supply-side measures that can help to mitigate livestock's environmental impact, substantively reducing meat consumption is required to ensure that food systems can sustainably feed the growing global population and would result in some benefits for human health too. Behavioural interventions to encourage changes in eating habits could help to reduce meat intake, but few such interventions have been implemented and rigorously tested. The aim of this thesis is to contribute towards addressing this evidence gap by generating empirical evidence on the effectiveness of behavioural interventions to reduce meat consumption through (i) systematically reviewing and synthesising the evidence on the effectiveness of interventions targeting conscious behavioural determinants or restructuring physical micro-environments; (ii) the development of a novel behavioural intervention (Replacing Meat with Alternative Plant-based Products, RE-MAP) to reduce meat consumption through the provision of meat substitutes, infographics, success stories, and recipes; (iii) a randomised trial evaluating the impact of RE-MAP on meat consumption, wider dietary changes, markers of health risk, markers of environmental degradation, and psychosocial factors related to meat and meat substitutes consumption; and (iv) qualitative interviews exploring the mechanisms through which the intervention might have delivered impact and recipients' experiences of the intervention. The results of my DPhil suggest that some behavioural interventions targeting conscious determinants of human behaviour and restructuring physical micro-environments can help to reduce meat consumption. Providing meat substitutes for four consecutive weeks along with supporting informational material is an acceptable strategy to help people eat less meat and emerged as one of the most effective interventions to reduce meat consumption tested to date. Specifically, RE-MAP led to a 63 g/d reduction in meat consumption at the end of the intervention and a 39 g/d reduction four weeks after the intervention completion. Based on these findings, future research should investigate how to translate the active components of the RE-MAP intervention into a scalable policy option.

Intentional weight loss requires self-regulation to override externally-driven behaviours. Self-regulation theory hypothesises that individuals automatically self-regulate when they find that their current state is not in line with their goals. In the context of weight management, this process involves self-weighing, contextualising weight measurements, reflecting on and evaluating previous behaviour, and planning and performing weight loss actions. The research presented in this thesis explored barriers to and benefits of self-weighing and self-regulation for weight loss in adults with overweight or obesity. In a think-aloud study, I investigated the extent to which self-regulation occurs naturally. I found that action planning was performed rarely, but was a significant predictor of weight loss. Individuals found self-weighing useful, but fluctuations hindered the interpretation of weight changes. With an observational analysis, I then explored why individuals trying to lose weight stop weighing themselves. I found individuals concurrently reduced their physical activity and gained weight preceding a stop in weight monitoring, suggesting that individuals lost motivation to lose weight and struggled receiving negative weight feedback. An app market review explored user reviews of weight tracking apps, finding that users gained motivation from receiving (graphical) feedback on their progress. Based on the findings from these three studies, I developed a weight loss intervention guiding individuals through the complete self-regulation process, whilst addressing several identified barriers. To support individuals` interpretation of weight changes, I employed daily weighing and weight tracking, but weekly reflection on weight changes. The intervention additionally encouraged individuals to experiment with weight loss actions on a daily basis, and evaluate their usefulness once a week. A randomised controlled trial (RCT) tested the early effectiveness of the intervention against daily weighing only, finding a significant weight loss effect at 8-week follow-up (-3.20kg, 95% CI=-4.49, -1.92). Participants found the intervention acceptable and feasible. Altogether, my research suggests that self-regulation can be an effective weight loss strategy when individuals are guided through it, supporting further research in this area. The long-term effectiveness of the intervention warrants further testing in a larger RCT.

A considerable percentage of the UK population are overweight (BMI≥25kg/m2) or obese (BMI≥30kg/m2). However, despite living in the same culture and exposed to a similar “obesogenic” environment, some individuals gain weight while others do not (French et al., 1995). This variability in weight control has been suggested to be associated with individual differences in eating behaviours (French et al., 2012). Certain factors, such as motivation (hedonic hunger and hunger status) as well as cognition (impulsivity and memory) may have an impact on eating behaviours and their relationship with weight control. Thus, the objective of this thesis was to explore individual differences in eating behaviours and investigate their relationship with motivation, cognition and weight control. The first experiment (Chapter 2) investigated the relationship between eating behaviours, motivation (hedonic hunger) and food consumption during an ad-libitum buffet. This study suggests that restrained eating behaviour was associated with higher overall energy intake, greater energy intake from unhealthy foods and greater energy intake from both high and low energy dense foods. However, no interactions between restraint and disinhibition or hedonic hunger was seen. Following this, the second experiment (Chapter 3) examined whether eating behaviours, such as disinhibition, restraint and hunger, change during a weight loss and weight maintenance period and whether they could predict changes in weight during these periods. Indeed, the results suggest that lower baseline restraint could predict greater weight loss during a low-energy liquid diet and interventions which increase restraint and decrease disinhibition may be beneficial for longer term weight maintenance. The third experiment (Chapter 4) was designed to investigate whether motivation and cognition influences eating behaviours. The results suggest that hedonic hunger, restraint and impulsivity may lead to higher levels of disinhibited eating behaviour. This study was also able to replicate the findings of previous literature suggesting that episodic memory is negatively associated with BMI (Cheke et al., 2016). Finally, following on from the previous study results, the fourth experiment (Chapter 5) included a more diverse sample of participants including dieters. The results provide evidence that individuals on a diet have poorer episodic memory ability than those currently not on a diet. This study also extended previous results suggesting that hedonic hunger (but also episodic memory and hunger) are important factors in disinhibited eating. Hedonic hunger was also shown to be important in levels of hunger.

Rates of overweight and obesity worldwide have increased substantially in recent decades. In England, over 60% of adults are now overweight or obese. Because excess weight is associated with higher risks of chronic conditions, including type-2 diabetes, cardiovascular disease, osteoarthritis, and certain cancers, as well as with premature death, it constitutes a major health burden. It is also associated with higher total healthcare spending, but how the associations differ in different healthcare settings is not well understood. I undertook a systematic literature review of studies that used individual participant data to estimate annual healthcare costs in relation to body mass index (BMI; in kg/m2). Compared to adults at healthy weight (i.e. BMI 18.5 to &LT;25 kg/m2), total annual healthcare costs were found to be 12% and 36% higher for overweight (BMI 25 to &LT;30 kg/m2) and obese (BMI >=20 kg/m2) adults, respectively. The associations were strongest for costs of medications (18% for overweight and 68% for obese adults), followed by inpatient care costs (12% and 34%), and ambulatory care costs (4% and 26%). Most of these studies used data from the United States, and were based on small-to-moderate numbers of participants, limiting their ability to reliably estimate healthcare costs in relation to grades of obesity or for different health conditions. There was no reliable evidence from individual participant data pertaining directly to the United Kingdom. Using data on over one million middle-aged and older women in the prospective Million Women Study, linked to routine administrative data on deaths, inpatient and day-case admissions, and primary care services, I estimated annual rates and costs of hospital admissions, primary care consultations, prescription items issued, and monitoring and diagnostic tests in relation to body mass index. Every 2 kg/m2 higher BMI beyond 20 kg/m2 was associated with 7.4% higher annual hospital admission costs, 5.2% higher primary care consultation costs, and 9.9% higher prescription costs, but no clear association with test costs was identified. Projecting these results to the total population of women aged 55 to 79 years in England in 2013, 15% (£662 million) of hospital costs, 11% (£229 million) of primary care consultation costs, and 22% (£384 million) of prescription costs were attributable to overweight and obesity. Type-2 diabetes, and cardiovascular and musculoskeletal diseases were the major contributing conditions to the total excess weight attributable costs. These findings will be useful to healthcare policy makers, commissioners, and providers in making investment and prioritisation decisions, and underline calls for greater investments in cost-effective interventions to reduce excess weight and prevent weight gain.

Background: The majority of adults in the UK are overweight or obese, and many embark on weight loss attempts, often without professional support. This dissertation set out to hone in on the cognitive and behavioural strategies used by adults with overweight and obesity attempting to lose weight, particularly in self-guided attempts, and to test the relationship between use of these strategies and weight loss success. Methods: A new taxonomy and questionnaire were developed to provide a framework to identify the cognitive and behavioural strategies used by individuals during weight loss attempts. The taxonomy was used in a systematic review and meta-analysis of self-help interventions for weight loss and in a systematic review of qualitative studies of self-directed weight loss. The questionnaire was used in an observational cohort study in adults with overweight and obesity trying to lose weight. Results: The taxonomy and questionnaire consist of 117 strategies. The qualitative review illuminated a range of attitudes and beliefs towards these strategies and highlighted the centrality of interpretation of self-monitored data. The quantitative review found that self-help interventions led to greater weight loss than unsupported attempts to lose weight at six months. In the cohort study, despite heterogeneity in the strategies employed, coherent patterns of behaviours emerged for individual participants. Strategies related to motivational support, dietary impulse control, and weight loss planning and monitoring were associated with greater weight loss. Conclusion: This dissertation demonstrates that self-help interventions can lead to significant weight loss and provides results to guide the content of such interventions. It maps out a previously uncharted area and provides a set of tools for further research and intervention development.