Describing a new food group classification system for UK biobank: analysis of food groups and sources of macro- and micronutrients in 208,200 participants di Piernas, C, Perez-Cornago, A, Gao, M, Young, H, Pollard, Z, Mulligan, A, Lentjes, M, Carter, J, Bradbury, K, Key, TJ, Jebb, SA