Last week found me out of my element. I had ventured into the wilds of Essex to look after my brother while my mother was away, and eschewed her offer of special walking boots to trek to the train station each morning. I was mildly affronted that she thought me too clumsy to navigate a simple 20-minute walk in my Converse trainers, but not as affronted as I was at 6am on Monday, when my feet skidded beneath me, my right shoulder hit the ground, and my cheekbone smacked the concrete. For the rest of the week, walking was very much out.

I also remembered how difficult it is to plan my diet when staying with my brother, because, like baby birds, there's always great competition between us for food. In fact, in my more self-indulgent moments, I still blame childhood sibling rivalry - rather than basic greed - for the fact that I eat so quickly. My brother Frazer is a brilliant cartoonist, a great animal lover, an expert on British sitcoms of the 1980s, and has the autistic spectrum disorder Asperger's syndrome. He is also a voracious eater - or would be, if he had the chance. My mother is very good at controlling his diet, making sure he balances it with a great deal of dog walking.

On Tuesday evening, when Frazer was out, I cooked up a huge pan of bolognese, and ate about a fifth of it. A fifth was a lot. Too much. I figured that Frazer and his support worker could have some the next day for dinner, and that would leave at least a bowl for me. Job done. Plan made. Diet organised.

On Wednesday I returned from work to find the pan empty. "My God," I said to Frazer, "you and Gary must have had absolutely LOADS!" "Oh no," he said blithely, "I ate it all." My eyes widened. "On its own, right?" "No, I had spaghetti too." My eyes bulged, at least partly with admiration. "Aren't you full?" He shrugged. "Not really," and reached for a banana. As did I. Losing this particular competition is always very slimming.