Is the NHS low-calorie diet programme delivered as planned? An observational study examining adherence of intervention delivery to service specification.

Obesity and Type 2 Diabetes Mellitus (T2DM) are chronic conditions with significant personal, societal, and economic impacts. Expanding on existing trial evidence, the NHS piloted a 52-week low-calorie diet programme for T2DM, delivered by private providers using total diet replacement products and behaviour change support. This study aimed to determine the extent to which providers and coaches adhered to the service specification outlined by NHS England. An observational qualitative study was conducted to examine the delivery of both one-to-one and group-based delivery of programme sessions. Observations of 122 sessions across eight programme delivery samples and two service providers were completed. Adherence to the service specification was stronger for those outcomes that were easily measurable, such as weight and blood glucose, while less tangible elements of the specification, such as empowering service users, and person-centred delivery were less consistently observed. One-to-one sessions were more successful in their person-centred delivery, and the skills of the coaches delivering the sessions had a strong impact on adherence to the specification. Overall, the results show that there was variability by provider and delivery mode in the extent to which sessions of the NHS Low-Calorie Diet Programme reflected the intended service specification. In subsequent programmes it is recommended that one-to-one sessions are used, with accompanying peer support, and that providers improve standardised training and quality assurance to ensure specification adherence.