The history of extreme endurance challenges (i.e. efforts lasting months, not a fortnight) shows a common theme:
participants expect to lose weight, and bulk-up in advance accordingly.
For challenges where food must be carried, or where quality nutritious food may be hard/unreliable to find on the way (I'm thinking the polar ice caps or the Himalayan Chain) then it makes complete sense to bulk up beforehand; the excess fat is the emergency buffer should things get tough or it means less food needs to be carried to begin with. The fact that they lose weight also means they've underfed themselves during the challenge and/or they've planned to do this by starting with the big buffer.
But that plan (deliberately underfeed at first) doesn't make sense to me for a 12 month long cycling challenge where he's regularly visiting places where the required food is available (e.g. home). Once the excess weight is lost then food intake will need to increase anyway which may throw things part way into the challenge. It's not as if the weight loss was going to be slow and steady for the full 12 months.
The Year challenge is about maintaining a steady state in all manner of things. You need to start each day pretty much in the same shape as the day before or you'll have to adapt something during the ride which is risky. Being a little bit more tired (e.g. sleep debt) each day isn't going to work for hundreds of days in a row if there's no scope for a long lie in once in a while. A weight loss of 50g a day (which equates to a calorie deficit of 385kcal a day) would add up to close to 3 stone over the course of a year, etc.
The only thing that makes sense for planned extra weight at the beginning is to help with insulation for the first few winter months (I know I benefit from this!).
But, going back to my original comment, I wasn't referring specifically to weight when I talked about fitness levels.
