Descriptive statistics for main study measures.

Food insecurity is associated with increased odds of anxiety and depression, but it is unclear whether this effect is causal, and if so, the timescale over which it occurs. We conducted a preregistered analysis of an intensive longitudinal dataset, the Changing Cost of Living Study, to explore evidence for causal processes linking food insecurity to anxiety and depression. Data were collected monthly between September 2022 and August 2023 from panels of adults in the UK (n = 244) and France (n = 240). Food insecurity predicted higher concurrent symptoms of anxiety and depression (measured respectively with GAD-7 and PHQ-8), controlling for gender, age, time and mental health in the previous month. Effect sizes were similar for GAD-7 and PHQ-8 scores. Changes in food insecurity produced changes in symptoms (within-individual standardised effects: 0.15 [95% CI 0.08-0.22] on GAD-7 and 0.11 [95% CI 0.03-0.18] on PHQ-8). The deterioration in mental health when participants became food insecure was of similar magnitude to the improvement observed when they became food secure. Consistent with Granger causality, food insecurity in the current month predicted poorer mental health in the following month after controlling for current mental health. These results support the hypothesis that food insecurity causes symptoms of anxiety and depression. The effects were rapid, occurring within a month of becoming food insecure, and were equally rapidly reversed. We conclude that policy interventions designed to reduce food insecurity would have immediate, clinically relevant, positive impacts on mental health.