Metabolic Health 6 MIN READ

How to Monitor Blood Glucose Levels & Fast Efficiently

Fasting is the buzzword in the nutrition realm but it has been practised by people around the world for centuries. It refers to a willing restriction or restraint on how we consume calories, whether as food or drink and can be immensely beneficial for metabolism, blood sugar levels as well as cardiovascular health.

Written by Sarvesh Talreja

Dec 14, 2021
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Fasting is the buzzword in the nutrition realm but it has been practised by people around the world for centuries. It refers to a willing restriction or restraint on how we consume calories, whether as food or drink and can be immensely beneficial for metabolism, blood sugar levels as well as cardiovascular health.

How can one monitor glucose?

Blood sugar can be observed by checking one’s glucose levels and can be tracked by doing a finger prick test or through a continuous glucose monitor (CGM). CGMs are devices that provide live data to users about their blood sugar levels. Typically, such devices monitor interstitial glucose levels, that is, the glucose levels from the fluids between cells, through a sensor.

Science of fasting and its impact on metabolic health

There are varied ways of practising fasting. Usually, people fast by consuming less food, or food with fewer calories, or by restricting access to food and drinks based on the hours one elects to eat, also called intermittent fasting. During a fast, our bodies lack their typical access to glucose, which positions the cells to use alternative means as well as materials to make their energy. Consequently, the body enters a state of gluconeogenesis, a natural process of creating its own sugar, the body’s preferred source of energy. This is aided by the liver as it converts non-carbohydrate elements like amino acids, lactate, and fats into glucose for energy. As the body preserves energy when we fast, the amount of energy our body burns while resting (called the basal metabolic rate) is more efficient. This results in a lower heart rate and blood pressure. At a later stage in a fast, the body can enter ketosis, a state during which the body fuels itself through stored fat. Ketosis is an optimised state for weight loss and balanced blood sugar. Fasting puts our cells under mild stress, catalysing their adaptation and enhancing their ability to cope, much like exercise does to our heart and muscles.

When one isn’t exercising, fasting has different effects on the body and blood sugar levels than during periods of fasted exercise. The duration of a fast is a major factor that dictates the nature and intensity of the fast’s impact. The early fasted state, lasting from 3-4 hours after eating to about 18 hours, sees a drop in blood sugar and insulin levels.

Fasting efficiently: Monitoring your blood glucose with a blood glucose meter or through a CGM, can help you focus your efforts on maintaining stable blood glucose levels. This can facilitate a triumphant fast.

Fueling: Avoiding fuel that is high-carb before you begin your fast can help your body. In fact, it can help with your metabolic flexibility, making sure that your body isn’t overloaded with glucose prior to shifting to fat burning. Consuming fuel that’s rich in micronutrients during your fueling window can facilitate the most efficient fast. A well-balanced diet of fiber, protein, fats and micronutrients can help you maintain stability in your energy levels throughout the day. You can observe your blood glucose graph to make sure that there are no surprises and that you have optimally fueled for the day.

Fast Break: Your consistent feeding time may get disrupted and you may feel the hunger hormones being triggered as per your non-fast routine. A blood glucose test can help you draw the line between fueling due to hunger hormones vs fueling when the body actually requires it, during a fast. This might get a little tricky as each body is different and reacts differently to fasting. On some occasions, you may feel fine but your blood glucose levels might be low. These cases can be taken individually and observed. Continuing your fast could be appropriate in certain cases instead of breaking it. This is because the body may switch to glycogen stores in the liver through glycogenolysis in short term fasts. During longer durations, it may switch to gluconeogenesis and synthesize glucose using lactate, pyruvate, glycerol, and amino acids. However, it is important to note that this is not medical advice. Please speak to your doctor before initiating any dietary regimen.

While breaking the fast, choose food items that won’t make your glucose levels soar and keep them in a steady range.

Fasted workout

When one is exercising or training fasted, a glucose test via a glucose meter or CGM can aid with real-time blood sugar data to guide the intensity of the exercise. The intensity of a workout can guide the energy source the body uses to fuel the workout, toggling between glucose and fat. Higher intensity exercises are typically fueled by glucose, and low or medium intensity exercises are fueled by fat.

Postpone any calorie intake until after the workout to execute a fasted exercise session. There are natural variations in the body’s glucose levels during a fasted workout. The glucose curve can indicate a rise in blood glucose, as well as maintenance of a steady level or a decline in blood glucose level. Each of these can have different meanings during a fasted workout.

Rise in blood sugar levels during a fasted workout

During fasted exercises of high intensity, the liver helps fuel the activity through glycogen. This means that although you are not consuming anything, the presence of blood sugar increases as it is being used by the body as fuel for the high-intensity fasted workout. It is recommended to regulate the period of intensity as blood sugar levels rise due to this phenomenon.

Stable blood sugar levels during a fasted workout

Glucose or blood sugar levels can remain stable during low or medium intensity exercises that take place in a fasted state. The stability of blood sugar levels indicates the body’s ability to continue its exercise trajectory for a sustained period of time. It indicates an energy-fueled physiological ability to maintain a status quo with regard to the activity being carried out.

Reduced blood sugar levels during a fasted workout

Glucose levels in the body can fall for a few reasons during a fasted workout. This occurs commonly when the body transitions to a state of physical activity or when its intensity increases. This is caused by a demand and supply gap for glucose, which fuels exercise in a fasted state. Sharper glucose drops take place as exercising in a fasted state may deplete muscle and liver stores of glucose over time. The duration of this occurrence may vary from person to person depending on their rates of carb and fat oxidation as well as the amount of liver glucose present before they begin a workout. A sharp plunge could manifest suddenly or over a short period of time.


Fasting is seeing a recent resurgence in adoption as well as conversations around fitness and nutrition. Monitoring your blood glucose can help you make real-time decisions about fasting efficiently. It provides insights into how your body is responding to your fast, as each individual’s metabolic health varies. This variation can cause different responses while fasting for different individuals. While it could be fine to continue your fast even if blood glucose levels dip to a certain degree, it is important to make sure that it doesn’t dip to dangerously low levels. This can cause cognitive decline. When working out in a fasted state, monitoring your blood glucose can provide an understanding of how primed you are for your workout, the intensity in which you could approach it and also how your body is responding to physical stress during a fast. Using stable sources of fuel during your fueling window can enable you to have a successful fast.

Disclaimer: The contents of this article are for general information and educational purposes only. It neither provides any medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention or alleviation of any disease, disorder or disability. Always consult with your doctor or qualified healthcare professional about your health condition and/or concerns and before undertaking a new healthcare regimen including making any dietary or lifestyle changes.


  1. Continuous Glucose Monitoring | NIDDK (
  2. fasting | Definition, Description, Types, Benefits, & Facts | Britannica
  5. 8 Health Benefits of Fasting, Backed by Science (

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