Fasting Blood Sugar Levels: What’s Normal? - Internal Medicine

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Understanding fasting blood sugar levels is crucial for maintaining overall health, especially for individuals with a family history of diabetes or other metabolic disorders. Fasting blood sugar (FBS) levels are typically measured after an overnight fast of at least 8 hours, but many people wonder how extended fasting periods, such as 15 hours or more, might affect these levels.

1. Normal Fasting Blood Sugar Levels: According to the American Diabetes Association, normal fasting blood sugar levels are generally considered to be below 100 mg/dL. Levels between 100 and 125 mg/dL indicate impaired fasting glucose, which is a risk factor for developing type 2 diabetes. A fasting blood sugar level of 126 mg/dL or higher on two separate tests indicates diabetes.

2. Impact of Extended Fasting: When fasting extends beyond the typical 8-hour period, such as your case of fasting for 15 hours, it is possible for blood sugar levels to fluctuate. In general, prolonged fasting can lead to lower blood sugar levels due to the depletion of glycogen stores in the liver. However, individual responses can vary based on factors such as metabolic rate, physical activity, and overall health.
3. Your Observations: You mentioned that your fasting blood sugar levels range from the 90s to 100-105 mg/dL after a 15-hour fast. These values are still within the normal range, but they are on the higher end of the spectrum. It’s important to note that slight variations in blood sugar levels can occur due to several factors, including stress, hydration status, and even the time of day.
4. Factors Influencing Blood Sugar Levels: The body’s response to fasting can be influenced by several factors:
- Hormonal Regulation: Hormones such as cortisol and adrenaline can increase blood sugar levels during periods of stress or fasting.

- Dietary Intake: The composition of your last meal before fasting can also affect your blood sugar levels. Meals high in carbohydrates can lead to higher blood sugar levels, even after fasting.

- Physical Activity: Regular exercise can improve insulin sensitivity and help regulate blood sugar levels. If you are physically active, this could contribute to lower fasting blood sugar levels.

5. Recommendations:
- Monitoring: Continue to monitor your fasting blood sugar levels regularly, especially if you have concerns about your family history of diabetes. Keeping a log of your readings can help identify patterns or triggers.

- Dietary Adjustments: Consider evaluating your evening meals. A balanced meal that includes proteins, healthy fats, and fiber can help stabilize blood sugar levels overnight.

- Consultation: If you notice consistent elevations in your fasting blood sugar levels or if you have concerns about your health, it’s advisable to consult with a healthcare professional. They may recommend further testing, such as an oral glucose tolerance test or an HbA1c test, to assess your overall glucose metabolism.

In conclusion, while your fasting blood sugar levels are mostly within the normal range, slight fluctuations are common and can be influenced by various factors. Maintaining a healthy lifestyle, including a balanced diet and regular physical activity, is key to managing blood sugar levels effectively. If you have ongoing concerns, seeking advice from a healthcare provider is always a prudent step.