Association between single nucleotide polymorphisms and weight reduction in behavioural interventions—a pooled analysis by Holzapfel, C, Sag, S, Graf-Schindler, J, Fischer, M, Drabsch, T, Illig, T, Grallert, H, Stecher, L, Strack, C, Caterson, ID, Jebb, SA, Hauner, H, Baessler, A