Thanks again, all. Neil D and Graham (Grab): I was like this (always ill in the winter) from the day I was born (for reasons outlined above), and I wasn't bought up a vegan. I became a vegan. Being one is, for me, not a choice: eating meat and dairy makes me extremely ill. (Won't go into the sordid details, but until I became a vegan and sorted myself out - the doctors couldn't - I was literally so ill I thought I'd never work again.) I have looked into the vegan diet because I have *had* to, to make me well. If you are careful, a vegan doesn't have to miss any nutrients a meat eater has. So I have plenty of 'fuel', but thanks muchly for the suggestion of aerobic exercise and weight lifting. I am seeing a friend tomorrow who goes almost daily to the gym, so I will discuss the possibilities with her. (I am neither underweight nor overweight, by the way, but do have a high metabolic rate.) Thanks again - my 'to do' list is getting longer, and I am heartily grateful to you all.