3 min readNew DelhiJun 22, 2026 09:32 AM IST
Can fasting blood sugar after 13 hours be higher than fasting blood sugar after 8 hours? Isn’t a longer fast supposed to lower glucose levels? In response to this Quora query, Dr Sukirti Misra, consultant endocrinologist at KIMS Hospitals, Thane, said that it may sound surprising, but fasting for a longer duration does not always result in a lower blood sugar reading. “Our bodies are constantly working to keep blood glucose within a healthy range, even when we have not eaten for several hours,” said Dr Misra.
DISCLAIMER: This article is based on information from the public domain and/or the experts we spoke to. Always consult your health practitioner before starting any routine.
One common reason is the dawn phenomenon. “In the early morning hours, the body releases hormones such as cortisol and growth hormone to help us wake up and prepare for the day. These hormones can signal the liver to release glucose into the bloodstream, causing fasting sugar levels to be slightly higher in the morning. This is especially common in people with diabetes because their bodies cannot produce or process enough insulin to counteract this natural spike,” explained Dr Misra.
Another factor is the body’s natural response to prolonged fasting. Dr Misra noted that as the gap between meals increases, the liver releases stored glucose to ensure a steady energy supply for essential organs, particularly the brain. “In some people, especially those with insulin resistance, prediabetes, or diabetes, this process can lead to a higher fasting blood sugar reading than expected,” said Dr Misra.
Does this happen only in people with diabetes?
Not necessarily. Mild fluctuations in fasting glucose can occur even in people without diabetes. “However, the effect is usually more noticeable in individuals with prediabetes, diabetes, or insulin resistance because their bodies may not regulate blood sugar as efficiently,” said Dr Misra.
Several everyday factors can also influence a fasting glucose reading, including inadequate sleep, emotional stress, illness, dehydration, late-night eating habits, and certain medications.
Should people be worried if they notice this pattern?
Not because of a single reading. “Blood glucose levels naturally vary from day to day, and one isolated value does not provide the full picture of a person’s metabolic health,” pointed out Dr Misra.
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What is more important is whether the pattern persists over time. Dr Misra mentioned that if fasting glucose levels are repeatedly elevated or seem inconsistent despite following testing instructions correctly, it is worth discussing the results with a healthcare professional. “Tests such as HbA1c and other assessments can help determine whether there is an underlying issue with blood sugar regulation,” said Dr Misra.
DISCLAIMER: This article is based on information from the public domain and/or the experts we spoke to. Always consult your health practitioner before starting any routine.