Art is abstract. Art could be anything you want it to be. Art is also the product of human creativity. That is why losing weight is also a form of art.
Losing weight is not confined to one strict regime that says you have to abstain from eating in order to lose weight. If that is so, losing weight would be boring and I’m sure nobody would want to become a personal trainer!
Like art, it is subjective and different people will have different ways on how they want to lose weight. That is why losing weight is a beautiful art.