Fasted training, exercise after an overnight fast, is a free scheduling practice shifting fuel use toward body fat, proposed to aid metabolic health. Its best-supported effect is in type 1 diabetes: morning sessions make low blood glucose less likely but high blood glucose afterward more common. Long or hard sessions go worse without food; hunger is stronger; fat-loss claims remain mixed. An optional tool for easy sessions; long-term value uncertain. (Full Review)
| Marker | Target | Why |
|---|---|---|
| HbA1c | 4.8–5.2% | Long-term glucose control |
| Fasting glucose | 75–90 mg/dL (4.2–5.0 mmol/L) | Baseline glucose; hypoglycemia margin |
| Fasting insulin and HOMA-IR | Insulin 2–6 µIU/mL; HOMA-IR below 1.0 | Tracks insulin sensitivity |
| Triglycerides | Below 100 mg/dL (ideally below 80) | Fat handling and metabolic health |
| Lean and fat mass | No established target; stable or rising lean mass vs own baseline | Detects muscle loss or fat change |
| CGM time in range (diabetes) | Above 70% at 70–180 mg/dL | Captures exercise-related hyperglycemia and hypoglycemia |
| Blood ketones (beta-hydroxybutyrate) | Below 0.6 mmol/L before exercise in type 1 diabetes or SGLT2 use | Screens for ketoacidosis risk |
Cadence: Baseline before starting; glucose-lowering drug users check glucose before and after each of the first 5–10 fasted sessions, then weekly; type 1 diabetes: review continuous glucose data for 24 hours after each new session type; blood tests at 12 weeks, then every 6–12 months; body composition every 6–12 months.