Interventions

Participants were either allocated to the intermittent fasting or smoking cessation arm based on inclusion criteria.

General measures

Both study arms were offered the opportunity to receive optional adjuvant exercise guidance tailored to their initial fitness levels. Participants were given the option to engage in three supervised exercise sessions throughout the study, focusing on resistance, endurance, and flexibility training. To enhance motivation and adherence, each participant was assigned a personal coach who provided support and guidance. Regular contact between the participant and coach, with a minimum recommendation of once a week, was encouraged. The coach also maintained records of participant compliance with the main study intervention.

Intermittent fasting arm

In the intermittent fasting arm, participants were randomised to receive a ketogenic supplement or not. To ensure balanced characteristics in each randomisation arm, we employed menopause- and BMI-stratified block randomisation (blocks of 4). This randomisation process was implemented using a secure Excel worksheet. Participants in the intermittent fasting arm followed a specific protocol consisting of an induction phase (1 month) and a maintenance phase (5 months) of a 16:8 intermittent fasting regime. This regime involved restricting eating to an 8-hour window each day (fasting for 16 h) and was guided by a dietician. During the first month, participants followed a 14:10 intermittent fasting regime, where fasting was limited to 14 hours instead of 16. In the intermittent fasting arm with the ketogenic supplement, participants were provided with a powdered supplement (Kanso MCTfiber, medium-chain triglyceride fiber sachet), which could be added to food or diluted in water.

Smoking cessation

The smoking cessation arm involved three group therapy sessions (6-12 participants). These sessions were ideally conducted within the first month of the study. Smoking cessation was targeted at the second session. Consequently, for each participant, a clearly defined smoking cessation date relative to baseline visit is available. Additionally, participants in this arm were offered the choice of two individual telephone appointments with a dedicated addiction counsellor to further support their journey towards quitting smoking.