The association of plant or animal food origin and processing level with BMI and waist circumference: a prospective cohort study of the UK Biobank.

Abstract

Body Mass Index (BMI) and waist circumference (WC) gain are key risk factors for cardiometabolic disease and mortality. Although plant-based diets are often promoted for health and sustainability, the rising inclusion of ultra-processed foods (UPF) within these diets raises concerns. This study assessed the associations of food origin (plant vs. animal) and processing level (UPF vs. non-UPF) with BMI and WC increase in a prospective cohort. A total of 17,374 participants aged 40-69 years from the UK Biobank cohort study were included. Dietary data were collected between 2009 and 2012, and follow-up assessments were conducted between 2012 and 2019. Dietary intake was assessed using a minimum of two and a maximum of five repeated 24-h dietary recalls. Foods were classified by plant or animal origin and processing level using the Nova system. Outcomes were defined separately for BMI and WC as increases of ≥5% and ≥10% from baseline to follow-up. Cox proportional hazards models were applied. During a mean follow-up of 5.3 years, 2477 cases of ≥5% BMI increase and 4567 of ≥5% WC increase were observed. A 10% higher energy intake from plant-sourced non-UPF was associated with 11% lower hazard of ≥5% BMI increase (HR 0.89, 95% CI 0.85-0.92) and 10% lower hazard of ≥5% WC increase (HR 0.90, 95% CI 0.88-0.93). A 10% higher intake of plant-sourced UPF was linked to increased risk of both BMI and WC increase (HR 1.10 and 1.09, respectively). Substitution analyses indicated that a higher contribution of plant-sourced non-UPF, at the expense of UPF (plant or animal), was consistently associated with a lower risk of study outcomes. Our findings highlight the importance of considering food origin alongside processing, showing that plant-sourced non-UPF may confer protective effects, whereas plant-sourced UPF contribute to adverse weight outcomes. Future research is needed to clarify the behavioural and biological mechanisms behind these findings. This research received funding from World Cancer Research Fund (WCRF UK), as part of the World Cancer Research Fund International grant programme.