Fasting vs after-meal blood sugar: how to log them separately

Short answer: tag every glucose reading with when you took it: fasting (8+ hours without food), before a meal, about 2 hours after a meal, or bedtime. Fasting and after-meal numbers have different reference targets, so keep them apart and compare like with like.

1. The four common timings

• Fasting: on waking, after at least 8 hours without food.
• Before meal: right before lunch or dinner.
• After meal: 1 to 2 hours after the start of a meal. Choose one and stick to it.
• Bedtime: before sleep.

2. Reference targets (ADA, for reference only)

For many non-pregnant adults with diabetes, the American Diabetes Association suggests a before-meal (including fasting) glucose of 80 to 130 mg/dL (4.4 to 7.2 mmol/L) and a peak after-meal glucose below 180 mg/dL (10.0 mmol/L), measured 1 to 2 hours after starting a meal. Below 70 mg/dL (3.9 mmol/L) is considered low. Targets are individualized, so your doctor may give you different ones. These numbers are not for diagnosing diabetes.

3. A simple logging routine

• Write the number, the timing tag and the date and time right after checking.
• Add a note when something was unusual: a big meal, exercise, illness, a missed dose.
• Look at fasting average and after-meal readings separately over a week or two, then bring the log to your appointment.

Doing it with Readband

Readband is a log for the numbers your glucose meter shows; it does not measure blood sugar. Each entry is tagged fasting, before meal, 2h after meal or bedtime, shown on a reference color band you can edit with your care team, and Readband keeps a separate fasting average. mg/dL or mmol/L, CSV export included.

For reference only. This guide does not diagnose or treat anything. Targets differ from person to person; follow your doctor or care team.

FAQ

Get Readband, a blood sugar log with fasting and after-meal tags (Google Play)

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