Gluttony, a virtue...

I sincerely hope that Gluttony is a virtue else Michael Phelps will be rotting in hell for eternity...

The athlete consumes 10,000 calories on an average every day, it is common knowledge that an urban male adult can sufficiently make do with 2400 calories on an active day. That means this gentleman's daily calorie consumption is over four times that of a regular person. Roughly 3,500 calories translate to one pound, simple math would suggest that he is putting on 3 pounds every day. His body fat content is only 8% so that means he is also burning a major chunk of the calories he consumes.

A healthy adult (in his 20s) can burn up to 500-600 calories per one hour of rigorous workout.
It is logical to assume a world class athlete can double it, so 1000-1200 calories per hour. Even if he works-out for 5 hours a day (a standard Olympic preparation), he would burn 5000 calories on the conservative end and 6000 calories on the aggressive end. That would still leave him with an additional 200o calories, even after discounting 2000 calories for daily usage.

Obviously he does not have calories piling on, or they are not visible at least (8% body fat, remember). So how are these 2000 calories accounted for. The only logical answer is that his metabolism is such that he is burning calories all the time,. If one were to see him after a world record breaking/setting swim he never seems out of breath. His metabolism might be facilitating expending of calories at all times.

Imagine the possibilities if your metabolism was such, you could eat all those kebabs and chocolates and fries and ice creams and cakes. You can always give in to the wafting aroma of a biryani or a steak. You could down a couple of bottles of wine everyday and not worry about your body's ability to break it down.

If a lady had such a metabolism, she would never have to worry about her weight or curves. She could but any dress she wanted without having to worry about weather she will fit in to, remember she can gain and lose weight at will. Losing post-baby fat is no longer a concern.

Sustainability is the only question...

Singing off...