Supercharge the whole planet's weight loss by spinning counterclockwise... Robbing the planet of it's angular momentum and extending night and day.

But optimize this by not running too close to c (or is it the contrary ? My restrained relativity courses are rusty)

In your reference frame nothing will be different, so it really depends on whether you want to loose weight for yourself or for others.

Except he had to accelerate to speed and back, so only our reference frame matters.