Does the British Columbia Farmers' Market Nutrition Coupon Program improve the diet quality and food security of parents and children with lower incomes? Protocol for a dose-response, pragmatic randomized controlled trial.

BackgroundThe British Columbia Farmers' Market Nutrition Coupon Program (FMNCP) provides lower-income households with coupons to purchase healthy foods at farmers' markets.AimThis pragmatic randomized controlled trial (RCT) will examine the effectiveness and cost-effectiveness of two higher subsidies for healthy food, compared to the usual FMNCP healthy food subsidy, on the diet quality (primary outcome), food insecurity, and other health-related outcomes of 276 parent-child dyads with lower incomes.MethodsIn this single-blind, three-arm, parallel-group pragmatic RCT, 276 parent-child dyads in lower-income households will be randomized to receive the usual FMNCP healthy food subsidy ($27/week) or a subsidy that is two ($54/week) or three times ($81/week) higher. Participants will receive 16 weeks of coupons that can be redeemed for up to 20 weeks. Outcomes will be assessed in one parent (18-64 years) and child (6-17 years) from each household pre-, mid-, and post-intervention. Dietary intake will be collected via two 24-h dietary recalls at each time point to calculate diet quality using the Healthy Eating Food Index-2019. Food insecurity and other health-related outcomes will be assessed using validated self-reported instruments. Mixed effects regression will assess the effects of the interventions, relative to the usual subsidy, on outcomes in parents and children. A full incremental analysis will quantify the cost-effectiveness ratios of the healthy food subsidies.SummaryThis dose-response RCT will show how the diet quality, food insecurity, and other health-related outcomes of parents and children vary according to subsidy amount.Trial registrationThe trial is registered at www.clinicaltrials.gov (NCT06992947).