A fasting score should never pressure you to continue when symptoms say stop. Readiness is context, not a challenge.
Body Insights combines supported recent recovery, sleep, glucose, fasting history, and safety context to estimate whether a planned fast looks more or less supported. Session progress and metabolic flexibility are calculated separately from actual completed sessions.
Should I fast today?
The readiness result describes how much support appears in the data before a fast. It is not a prediction that fasting will feel safe or beneficial.
The useful question is not whether one reading is perfect. It is whether the same signal keeps moving in a way that matches your sleep, symptoms, activity, and recovery. Body Insights keeps the underlying rows visible so the headline never has to stand alone.
What goes into the calculation?
Body Insights reads the available inputs from Apple Health and the app's own history. It does not create missing wearable measurements.
- Recent sleep, readiness, stress, and illness context
- Glucose context when a compatible CGM is available
- Past fasting sessions, duration, completion, and recovery history
Supported pre-fast signals are evaluated before the session. Progress, completed stages, glucose change, and long-term profile use the recorded session timeline rather than the same readiness formula.
What happens when data is missing?
No CGM does not automatically block readiness, but it removes metabolic context. Missing safety or recovery data must reduce confidence.
This matters because "not measured" is not the same as "bad." A watch charging overnight, an incomplete Health permission, or a short history can reduce what the calculation knows without saying anything negative about your body.
What can change the result?
Illness, symptoms, poor sleep, medication, recent fasting, exercise, and fresh glucose can change the guidance.
If a result looks surprising, check the input rows first. A single missing night, unusual workout, illness, medication change, travel day, or sensor gap can explain more than the headline number.
What can this calculation not tell you?
The calculation cannot decide whether fasting is medically appropriate. Pregnancy, eating-disorder history, diabetes treatment, and other conditions require professional guidance.
Body Insights is a pattern-reading tool, not a diagnostic device. Bring persistent, severe, or worrying changes to a qualified clinician, especially when the number and how you feel disagree for several days.
Read the reason, not only the number
Use the result as one reason to pause and check how you feel. Stop or seek help when symptoms or your clinical plan say to, regardless of the score.
Body Insights reads data that Apple Watch and compatible devices place in Apple Health. The purpose of this page is to make that translation inspectable without publishing gameable score weights or pretending a wearable estimate is a clinical test.