What is Fasting Blood Glucose?

Fasting glucose is calculated by gathering your glucose level after fasting for 8-12 hours. The target fasting glucose range is 72-100 mg/dL, but there are several factors that can contribute to a higher than average fasting glucose number. The goal is to take a deeper look into what could be causing an elevated fasting number in the morning. Keep in mind that we can not base anything off of a single number, as it is normal to see fluctuations in fasting numbers. Rather, we would like to look at the trend and see if there are nutrition and lifestyle actions to take to help improve the fasting number.

One major contributor to a higher fasting glucose is consuming a higher carbohydrate meal for dinner or eating late at night. Ideally, we would like to stop eating at least 3 hours before bed, or optimally when it is still light outside since our hormones run on a circadian rhythm and we have a decrease in carb tolerance at night.

Poor sleep, alcohol, and higher stress levels can also impact fasting numbers. Short or disrupted sleep is associated with poor glucose regulation. Studies of healthy young adults exposed to recurrent partial sleep deprivation showed decreased glucose tolerance and insulin sensitivity. Also, If you consume alcohol in the evening, you might notice that your glucose spikes are delayed (sometimes for several hours). The reason behind this is the concept of oxidative priority. Your body prioritizes what it metabolizes first, based on what’s most easily stored. Since your body has no capacity to store alcohol it gets metabolized first followed by carbs, protein and fat. This prioritization delays the breakdown of carbs into glucose until later in the night. Any stress response can cause a spike in glucose levels for some, including nightmares.

If your glucose levels are spiking between 4am and 8am, what you’re likely experiencing is a common phenomenon known as the “Dawn Effect.” Essentially the body releases glucose back into the bloodstream from glycogen stores in the liver in the early morning hours. It’s the body's way of giving you a little fuel to wake-up and take on the day. While the Dawn Effect can be of some concern for those with diabetes, it's usually not considered a problem with non-diabetics.

It is important to look at all of your glucose data, and to prioritize looking at postprandial spikes. If you see a trend of higher fasting levels along with higher spikes and/or spikes with a larger area under the curve, then we recommend taking a look to see if there are areas of opportunity to work on to help mitigate those spikes. 

*It is important to know that your body responds slightly differently to each sensor. This means you can have sensors baseline at different levels, as one may baseline at 85 and the next one could baseline at 95. There is no cause for concern over this, as it is best to look at the relative spikes to food, stress, sleep, and exercise versus the absolute numbers.

Learn more about fasting glucose.