Ana I think they email you in a year's time and ask you to do the test again.
I haven't had any junk from them since I did the test.
I am normally quite suspicious of things - I filled in one questionnaire which seemed to be promising skin cream samples, only to get to the end and be asked to pay £65 for a jar of skin cream. I exited that one pretty quickly.
But as far as I can see Food for the Brain is a genuine organisation carrying out on-going research, aiming to build an evidence base to help in early diagnosis and management of dementia.