When my oncologist first told me I would be having radiotherapy of my oesophagus, one of the pieces of advice he gave me was to eat as much as possible in the weeks beforehand. My dietician said I ought to maximise my intake of protein, carbohydrates and fat (when was the last time your doctor told you to do that?). They were concerned that the damage to my oesophagus would make it difficult for me to eat and so I might lose a lot of weight. Since it was December when I was diagnosed, it was not difficult to follow their advice (especially with two very concerned families who liked to express their love by supplying us with lots of food, not the mention the many friends and members of our church family who also cooked us meals). As a result, I gained 5-10 kilos on top of my usual weight, putting me into the 'overweight' range, according to my BMI (Body Mass Index).
Radiotherapy did leave me on a liquids-only diet for a few weeks (and a water-only diet for a couple of days at one point. Even milk or very thin soup was too painful), but being tired and feeling unwell also greatly reduced my physical activity, so I never lost much of the weight I'd so rapidly gained.
Today, I remain a little above the 'normal' BMI, yet my oncologist has always been far more worried that I will start losing weight rapidly than he is concerned at my being slightly overweight. An article in today's Sydney Morning Herald might help explain his reaction: a US study has found that "being up to nearly 14 kilograms overweight reduces by 40 per cent your chance of dying from a range of common diseases and risks, not least because it improves your chances of recovering from surgery, injury and infections."