How do you explain to an employer or coworkers why you're suddenly eating very differently at work?

Most people don't feel obligated to give a detailed medical explanation to coworkers. A simple "I'm working on some health stuff" or no explanation at all is completely reasonable. For situations where more context feels necessary (a manager noticing reduced energy during a dose increase, for example), keeping it general rather than disclosing the specific medication is a common approach. It's personal medical information, not something owed to a workplace by default. References: https://obesitycanada.ca/healthcare-professionals/adult-clinical-practice-guideline/