What Happens to Blood Sugar While Fasting? Testing Rules and Safety Thresholds

Fasting for 12 to 15 hours during summer in Pakistan fundamentally alters your body's energy fuel supply. Understanding how your liver and pancreas adapt during daylight hours helps you monitor your health with confidence, and know exactly when a reading means it's time to stop rather than push through.

The Physiology of Fasting

Ramadan fasting is different from an ordinary skipped meal: it typically runs 10 to 21 hours depending on the season and your location, and is repeated every day for 29–30 consecutive days, according to a clinical overview of diabetes management during Ramadan published on NCBI Bookshelf (opens in a new tab). Your body moves through several distinct metabolic phases across that window:

1. 1Early Hours (0 to 6 Hours After Sehri): Your body digests carbohydrate fuel from your pre-dawn meal. Insulin moves glucose into cells, and blood sugar is typically at its most stable during this window.
2. 2Mid-Day Phase (6 to 12 Hours): As blood glucose drops, your liver begins releasing its backup stored sugar (glycogen) to keep your brain and muscles fuelled.
3. 3Late Afternoon Phase: Liver glycogen stores become depleted. Your body begins breaking down fat for fuel (a normal process called lipolysis). In people taking insulin or sulfonylureas (like glimepiride/Getryl or gliclazide), this phase carries the highest risk of low blood sugar (hypoglycemia).

This is not a theoretical risk: clinical reviews of Ramadan fasting note that roughly 70% of hypoglycemia episodes occur in the last six hours of the fast, right before Iftar — which is exactly why testing in the mid-to-late afternoon matters so much.

Does Finger-Prick Blood Testing Break Your Fast?

A very common myth in Pakistan is that pricking your finger to test blood sugar invalidates or breaks your fast. This is completely false.

Major Islamic Fiqh councils globally (including the International Islamic Fiqh Academy and leading scholars in Pakistan) have explicitly ruled that checking blood sugar via finger prick or wearing a continuous glucose monitor (CGM) DOES NOT break the fast, as it does not introduce nourishment into the stomach. The IDF-DAR practical guidelines (opens in a new tab) actively encourage self-monitoring of blood glucose as a cornerstone of safe fasting, precisely because it carries no religious cost and real medical benefit.

• If blood sugar drops below 70 mg/dL (3.9 mmol/L) at any time during the day — the IDF-DAR guidelines (opens in a new tab) specifically flag this threshold as the point to act, especially if you took insulin or a sulfonylurea at Sehri.
• If blood sugar drops below 60 mg/dL (3.3 mmol/L) at any time — this is unambiguous and requires breaking the fast without delay, since levels can fall further within minutes.
• If blood sugar rises above 300 mg/dL (16.7 mmol/L) — and if you use insulin or have type 1 diabetes, check for ketones if you're able to; ketones alongside a high reading are a sign of possible diabetic ketoacidosis and need urgent medical attention.
• If you experience clear symptoms of low sugar (shakiness, cold sweat, confusion, dizziness) even before testing — treat the symptoms first, test when you can.
• If you notice signs of significant dehydration — such as dizziness on standing, a very dry mouth, dark urine, or confusion — since long fasting hours in Pakistan's heat raise this risk, a point also emphasised by the American Diabetes Association's guidance on Ramadan management (opens in a new tab).
• If you feel seriously unwell in any way that doesn't match your usual fasting experience.

Why Two Different Low-Sugar Thresholds?

You may notice guidance mentioning both 70 mg/dL and 60 mg/dL. The distinction matters: a reading below 70 mg/dL is a warning to test again soon and be ready to act, particularly early in the fast, while a reading below 60 mg/dL — or any reading with clear hypo symptoms — means act immediately, with no waiting period. Treat these as a graded alarm system rather than a single line: the lower the number, or the worse you feel, the less time you have to respond safely.

“Checking your blood sugar during daylight hours is a vital safety tool—it protects your health and gives you total peace of mind.”

Log your daytime Ramadan readings

Track your mid-day and late-afternoon readings in Diatic to stay safe throughout the holy month.

Log a reading (opens Diatic on Google Play in a new tab)