Possible Clues:

• One trying to lose
• Member of Weight Watchers, German chap?
• Keto adherent, e.g
• Person counting calories
• German slimmer
• German chap, one eating less?
• What you might call someone in Munich who isn't a bad loser?
• One of those with as a reputation as a loser is given this name in Munich
• One of those with a reputation as a loser produced a hamburger, by which one is called perhaps?
• German fellow's regimen accepted with bit of hesitation