Knowledge, attitudes, and behaviors toward the planetary health diet in France: a survey among patients, healthcare professionals, and farmers-bakers’ customers

The Planetary Health Diet (PHD), developed by the EAT–Lancet Commission, provides a comprehensive framework to promote human and planetary health through dietary transformation. Despite its benefits, adoption of the PHD remains limited in high-income countries like France. This study aimed to evaluate knowledge, attitudes, and behaviors (KAB) related to the PHD across diverse French populations and identify determinants of inadequate KAB. This cross-sectional quantitative study was conducted between April and June 2024 under the BIOQUALIM protocol. Eligible participants were adults (≥ 18 years) fluent in French and included healthcare professionals and patients from the Hospices Civils de Lyon (HCL), as well as farmers-bakers’ customers from the Rhône-Alpes region. A validated 89-item questionnaire was administered via paper and digital formats using a convenience sampling strategy. KAB levels were calculated from a structured scoring system. Descriptive statistics and multivariate logistic regressions were used to assess KAB levels and their sociodemographic determinants. Among 10,500 individuals approached, 1,388 completed the survey (79.6% HCL professionals, 6.4% patients, 14% farmers-bakers’ customers). Only 3% demonstrated an adequate overall KAB score; knowledge adequacy was observed in 61%, while attitude and behavior adequacy remained critically low (3.5% and 0.2%, respectively). Inadequate KAB was significantly associated with omnivorous diets (OR = 3.38), female gender (OR = 2.54), patient status (OR = 13.84), while low food budgets increased risk (≤ 50 €/week, reference OR = 1) and higher weekly expenses were protective (OR range 0.42–0.57). Protective factors included older age (≥ 60 years; OR = 0.17) and higher weekly food expenses (>€100). Although awareness of sustainable diets is rising, behavioral adherence to the PHD remains poor, highlighting a pronounced knowledge–action gap. Cultural norms, economic limitations, and institutional structures still delay dietary change. Policy efforts must extend beyond education to include economic answers, culturally adapted messages, and systemic reforms to enable a fair and sustainable food transition.