Habit degradation strategies promote faster early reductions in unhealthy snacking habit strength in intensive longitudinal randomised controlled trial

Abstract Habits are a key determinant of sustained health behaviour. However, little is known about how to degrade unhealthy habits in daily life. This preregistered single-blind randomised controlled intensive-longitudinal trial tested the efficacy of habit degradation strategies (substitution, inhibition, reduced accessibility) and reward in degrading (i.e. decreasing) an unhealthy snacking habit in daily life using a 3×2 factorial (plus control group) design. 313 participants (mean age 32 years) were randomised via smartphone app to complete 13 weeks of daily self-report assessments. From 13,922 habit strength (Self-Report Behavioural Automaticity Index) observations, within-person time series were modelled using asymptotic functions and generalised additive models to extract indicators of habit change. Habit strength declined over time across groups, with steeper reductions during the first week of the intervention phase. Analysis of variance indicated the rate of change during week 1 to be significantly greater in intervention groups compared to control. Analysis of covariance and logistic regression did not find evidence for differences between strategy or reward condition in magnitude of change, likelihood of reaching asymptote, or time to asymptote. Results suggest using habit degradation strategies may accelerate early reductions in habit strength. Limitations include suboptimal adherence to experimental manipulations and self-report measurement of habit strength. Findings are discussed considering the opportunities and challenges of experimental intensive longitudinal designs in real-world settings.