“You should change your workouts and diet based on your menstrual cycle.”
Moderate confidence that a universal cycle-based workout or diet schedule is not supported. A performance meta-analysis found only a trivial average early-follicular effect with low-quality evidence and wide variation, while a nutrition review found inconsistent interventions and no consensus sufficient for general recommendations.
Current evidence does not support a rule that everyone who menstruates should restructure workouts and diet by cycle phase. Average performance differences appear trivial and highly variable, and nutrition studies do not establish a universal phase-based plan.
Cycle symptoms can matter even when a fixed calendar does not. Training goals, recovery, sleep, energy intake, contraception and individual symptoms can be more useful guides than a universal cycle-syncing schedule.
You do not need to rebuild your workouts or diet around every cycle phase. Individual symptom patterns can still justify practical adjustments.
Track symptoms and performance if that is useful, then adjust food, rest or training to your own repeated pattern instead of following a rigid calendar.
Similar claims on Cycle syncing (training & nutrition by menstrual phase)
Listen to your body and adjust intensity around symptoms if you need to, but don't feel obligated to buy a cycle-syncing program or overhaul your training calendar - the performance case for it isn't established yet.