There are many different reasons that fasting glucose values could be elevated. One factor to keep in mind is that the CGM device is allowed by the FDA to have up to a 15% variation from what you would receive from a full lab draw at a physicians office. So your true fasting value may be lower or higher than what the CGM is reading. The most important thing to consider is the overall trends rather than an exact number. The change in glucose is very precise and reflects real changes.
With that being said, below are a list of the major factors that may be causing your fasting glucose levels to rise.
What and when you ate the night before - both the content of your meals, portion sizes, and what time it was consumed can have an impact on fasting values. Meals that are high in processed or refined carbohydrates can cause our glucose values to soar while we sleep. Additionally, we tend to not process food as well later in the evening so all meals, regardless of the meal types, can cause fasting levels to rise if they are eaten late at night.
Overall stress levels - stress causes elevated cortisol which leads to increase glucose production by the liver.
Low physical activity levels.
Poor sleep quality and/or quantity.
It is actually fairly common to experience higher fasting and nighttime glucose values if you follow a strict very low carb/keto diet for a prolonged period of time. It appears to be a natural adaptation that the body makes to assure there is glucose present for organs that require glucose, such as the brain.
If you have questions about your fasting glucose values, ask your health coach!