He must be buying piles of sweets from the trolley to maintain a weight that high. If he's on a calorie controlled diet for the normal meals then even 2 packs of quavers (198 calories total) and a few bottles of fizzy pop - which was what they found he was buying - wouldn't account the complete lack of weight loss, as he'd need to be maintaining his usual number of calories to stay where he is. So either the person on the trolley is allowing him to buy most of their stock every day, or someone is bringing him food in. You don't maintain weight at 47 stone unless you're eating serious calories.