Efficacy, acceptability and experiences of very low energy diets in adults with type 2 diabetes

Abstract

Aims: Type 2 diabetes (T2DM) has traditionally been regarded as an irreversible and progressive chronic condition. Recent evidence suggests that T2DM can be reversed by dietary restriction of energy intake through very low energy diets (VLEDs), indicating its potential for the treatment of one of the most prevalent chronic conditions associated with overweight and obesity around the world. VLEDs represent the most rapid, non-surgical method of weight loss (WL), but evidence showing acceptability of VLEDs and their short- and long-term efficacy in people with T2DM is limited. This PhD project aims to: 1) determine efficacy of VLEDs for weight loss and diabetes remission; 2) explore peoples` experiences with adherence to VLEDs; and 3) evaluate acceptability of VLEDs. In order to determine long-term sustainability of weight loss through VLEDs, this project further aimed to 4) explore peoples` experience with weight maintenance following weight loss through VLEDs; 5) evaluate acceptability of different plans for weight loss maintenance (WLM); and 6) explore changes in peoples` experiences from the beginning of weight loss through to weight loss maintenance. Methods: A mixed-methods approach was used to achieve the above aims. Chapter 1 provides a review of literature relating to T2DM and its treatments. Chapter 2 gives an overview of the relevant theoretical perspectives and provides a theoretical background to this PhD project. To determine efficacy and acceptability of VLEDs from the existing literature, Chapter 3 presents a systematic review of controlled trials and qualitative studies of individuals with T2DM that compared the efficacy of VLEDs with standard care, minimal interventions and other WL interventions. Chapter 4 briefly describes the Counterbalance Study, which investigated the principle determinants of long term reversal of T2DM, consisting of a 2-month WL period with VLEDs, followed by a 6-month WLM phase. The Counterbalance Study was independent of this project, but provided a platform for all qualitative work I have conducted within this PhD. In Chapters 5 and 6, I employed qualitative methods to explore experiences with a VLED amongst people with T2DM, who were engaged on the Counterbalance Study, and to determine acceptability of the VLED as an intervention for weight loss and diabetes remission. For this study, I interviewed 15 of 30 participants in the Counterbalance Study at the start and the end of the VLED. I conducted thematic analyses to find out about peoples` motivation to take part in the Counterbalance study, their experiences, their perceived barriers and facilitators to adherence with the VLED, about behavioural strategies they used v to overcome the barriers, and about their views on acceptability of the VLED. In Chapters 7 and 8, I employed the same qualitative methods and interviewed 16 and 15 participants of the Counterbalance Study after the WL and the WLM phases respectively. The interviews aimed to explore peoples` experiences with the WLM phase including their motivation, experience, barriers and facilitators to adherence, behavioural strategies they employed, and support needs at this stage. In the last empirical chapter (Chapter 9), I analysed the narratives of 11 participants who were interviewed at all three stages (baseline, end of WL and end of WLM) to identify themes of change, and to find out how peoples` experience of WL relates to experience of WLM. Results: Chapter 1 described T2DM and its complications, comorbidities and the impact of T2DM on peoples` health and the economy. It provided an overview of the current invasive and non-invasive treatments of T2DM, introduced VLEDs and the existing evidence of their efficacy and acceptability. Chapter 2 provided an overview of the psychological literature relevant to WL, WLM and eating behaviours. It introduced the behaviour change theories relevant to this thesis, discussed their strengths and weaknesses, and discussed their utility in health psychology research. This chapter also provided a springboard for hypotheses that I further explored in the qualitative studies in Chapters 5-9. The systematic review in Chapter 3 identified 9 controlled trials that were included in meta-analyses and narrative syntheses. These analyses showed that VLEDs induced greater WL than minimal interventions, standard care or low energy diets, and equal WL compared to bariatric surgery, at 3 and 6 months. It also showed that a larger difference in energy prescription between the intervention and the comparator arms is associated with larger differences in WL and fasting blood glucose levels at 3 months. No qualitative studies were suitable for inclusion in the systematic review, however acceptability of VLEDs was suggested by attrition rates, which did not differ between the VLED and the comparator groups at any measurement point. The qualitative study of peoples` experiences with and acceptability of VLED in Chapters 5 and 6 found that the VLED was perceived as generally highly acceptable among motivated individuals involved in a clinical study. The following themes reflected the experience of people with a WL through VLEDs: 1) improving health-related quality of life and 2) enhancing appearance, which were the main motives for the participants to take part in the study; 3) exceeded expectations, and 4) positive feedback loop, which stimulated the continuous motivation to adhere with the diet, and 5) facilitation of adherence, vi including behaviour-regulation strategies that the people used to overcome barriers to adherence. In Chapter 7 and 8, I extended the qualitative enquiry to the WLM phase of the Counterbalance Study: The following themes reflected the participants` experience with and acceptability of the WLM phase: 1) shifting of goals, 2) from uncertainty to regaining control, transcending which was the notion of a 3) shifting identity. Uncertainty about transition to regular food and weight maintenance and a progress towards building healthier habits and growing control of behaviour was a common denominator of the themes. To facilitate successful WLM, people used behaviour-regulation strategies of monitoring and compensation by physical activity and calorie restriction. Acceptability of the WLM phase and WLM success were related with: 1) preference for a WLM plan; and 2) satisfaction with WL and WLM outcomes. The participants also evaluated which intervention features were useful and offered suggestions for improvement of the intervention. Lastly, in Chapter 9 I identified changes in the peoples` experiences with weight management over time. The results show that success during WL and WLM is facilitated by the experience of transition from behavioural inter-dependency (with other people) to behavioural independence, and by adaptation of their mindset from a regimented one during WL to more flexible one during WLM. The interviews also showed that behaviour change can be “contagious” and other people may benefit from one`s behaviour change. The longitudinal narratives also highlighted the shift in identity people experience during the process of behaviour change. Conclusions: The empirical studies in this PhD project found that VLEDs are effective and acceptable for WL and remission of T2DM among highly motivated individuals within a clinical setting. People who struggle adhering to a VLED or WLM following a VLED may use behaviour regulation strategies identified in this PhD to facilitate adherence. Social support was an important facilitator both, WL and WLM. The WL and WLM interventions can be improved by enabling the participants to meet each other to exchange experience, tips and to support each other. Monitoring and providing feedback on performance during the WL and WLM phases stimulates continuous effort and clinical support beyond WLM might facilitate long-term sustainability of the achieved outcomes. Future studies should explore efficacy and acceptability of VLEDs in a primary care setting, with more limited resources.