I remember in Tim Ferriss's "The 24 Hour Body" he had a section about Michael Phelps, who was reported to have consumed 12000 calories a day when training - the

I remember in Tim Ferriss's "The 24 Hour Body" he had a section about Michael Phelps, who was reported to have consumed 12000 calories a day when training - the explanation one of his subjects came up with was that (a lot of) the calories were used in maintaining body temperature in the relatively cold water of the pool.