National survey of the Portuguese elderly nutritional status: Study protocol Madeira, Teresa, Peixoto-Plácido, Catarina, Goulão, Beatriz, Mendonca, Nuno, Alarcao, Violeta, Santos, Nuno, De Oliveira, Rita Machado, Yngve, Agneta, Bye, Asta, Bergland, Astrid, Lopes, Carla, Nicola, Paulo, Santos, Osvaldo, Clara, João Gorjão (2016)