Blog Diets Fasting Does Fasting Lower Blood Sugar? The Facts

Does Fasting Lower Blood Sugar? The Facts

Intermittent fasting is the new hype in the fitness world. Also known in its most popular form as the time-restricted eating plan, it involves alternating between periods of eating and fasting. This regime has several branches, leaving one to choose according to its feasibility.

The primary health claim of intermittent fasting is an improvement of certain markers of metabolic health including improved insulin sensitivity(6), The key objective of people adhering to intermittent fasting is usually weight loss, which tends to happen due to an overall decrease in calorie intake. It is important to note that several other lifestyle changes should be integrated into this routine. This includes more exercise and healthier balanced diet plans.

Fasting may sound helpful for people with diabetes, but it isn’t the ultimate treatment. The American Diabetes Association has no recommendations about fasting as a solution for people with type 2 diabetes. They instead support reducing overall carbohydrate intake to improve hyperglycemia. If you are dealing with blood sugar problems and want to use IF as a solution, you should go through this guide, but more importantly, work closely with your healthcare provider. They will need to monitor you and may make adjustments to your medication along the way.

Below, we have answered the most common question, “Does fasting lower blood sugar?” Followed by its recommended duration and benefits, this guide can help you plan a fasting schedule.

Does Fasting Help Lower Blood Sugar?

Fasting has been suggested to positively impact insulin resistance and help reduce blood sugar levels. Any practice that reduces your insulin resistance can affect your blood sugar and may protect you against Type II Diabetes.

A systematic review and meta-analysis published in 2022 found that intermittent fasting helped lower several markers of glucose metabolism and insulin resistance in people with impaired glucose and lipid metabolism (6). Another study from 2018, this time using mice with diabetes, found that intermittent fasting helped them live longer and protected their eyes from damage (11). 

Basically, insulin resistance can cause blood sugar levels to rise beyond a healthy range, which puts a person at risk of diabetes complications. Controlling blood sugar is essential for individuals with diabetes or pre-diabetic conditions. 

See also
Fasting vs Starving: Knowing The Difference Will Save Your Life

However, not all studies agree or support the use of intermittent fasting for blood sugar control. There will also be unique differences between individuals. 

Therefore, seeking help from a medical professional when creating a fasting plan is essential. It may be unsuitable for certain individuals, and others may need to be medically monitored.

does fasting lower blood sugar  

Does Your Blood Sugar Drop When You Fast?

Yes, the blood sugars generally drop when you fast. Here is what happens:

  1. Your body stores glucose in your liver and muscles.
  2. When you don’t eat food, your body uses the stored sugar for energy. 
  3. Your body starts burning fat for energy when all the stored sugar is used up. It also turns some protein into glucose to make sure your blood sugar does not drop dangerously low.

One of the drawbacks of fasting is that the blood sugar level may go extremely low. This condition is called hypoglycemia. It occurs when an individual’s blood sugar levels go below 70 mg/dL. It is important to watch out for and prevent low blood sugar because sugar is the main energy source for your body and brain. Low blood sugar can cause different symptoms and even serious health problems like seizures, fainting, and even coma (8).

Some common symptoms of hypoglycemia include:

  • Dizziness or lightheadedness
  • Shaky, weak, or experiencing convulsions
  • Racing heart or unsteady heartbeat
  • Irritability
  • Vision or speech problems
  • Fatigue
  • Headache

If you are going through any of these problems, you should seek help immediately. Talk to your doctor about ways to avoid hypoglycemia and what to do when you experience it. Also, skip intense workouts while fasting, which can make your blood sugar drop too quickly. Instead, plan your exercise for when you break your fast or after dinner.

Try to watch for the signs of low blood sugar. If you start feeling too shaky, you should stop fasting right away. Try eating a glucose gel or sugary drink followed by a balanced meal when the blood sugar returns to normal. Don’t forget to consult a registered dietitian or a healthcare professional for personalized advice on managing blood sugar levels.

See also
Keto Vs Intermittent Fasting: Is One Better Than The Other?

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How Long Does Intermittent Fasting Take to Lower Blood Sugar?

The answer to this question depends on how many hours you spend fasting. Some notable fasting methods which are based on different periods include the following:

Early Time Restricted Eating

This type of intermittent fasting (IF) means you eat only during a set time each day. A common plan is the 16:8 method, where you fast for 16 hours and eat within an 8-hour window. Early means that most calories are consumed earlier in the day, so your feeding window might start around 8:00 am or whenever you first wake up in the morning. 

Research presented at the Endocrine Society’s annual meeting 2023 suggested that following an early time-restricted eating plan for just one week may help keep blood sugar more stable and lower the amount of time it’s too high (1). This means that eating earlier in the day might be a way for people who are overweight or at risk of developing diabetes to keep their blood sugar levels healthy and possibly prevent them from getting type 2 diabetes.

Periodic Fasting

This type of fasting means you either don’t eat at all or eat very little for 24 hours at a time. Two examples are the 5:2 diet and Eat Stop Eat.

  • 5:2 Diet: You eat normally for 5 days of the week. On the other 2 days (not back-to-back), you only eat about 500 calories.
  • Eat Stop Eat: You completely avoid food and drinks with calories for 24 hours, once or twice a week. On other days, you eat healthy, balanced meals.

Researchers from the University of South Australia studied the 5:2 fasting method in people with type 2 diabetes. They did two studies, and both found that after 12 weeks, people’s blood sugar levels (A1C) and weight were reduced, similarly to those who did continuous energy restriction (typical dieting) (14)(5).

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The Benefits of 40 Hours Fasting: Do They Outweigh The Potential Risks?

Alternate Day Fasting

With this type of fasting, you switch back and forth between a “fast day,” where you eat very little or nothing (up to 500 calories), and a “feast day,” where you can eat as much as you want.

It is important to scan the perks and drawbacks of all fasting methods. You shouldn’t opt for the longer fasting windows at the initial stages. Take baby steps and gradually move towards longer fasting hours. You can start with a few days and see how it impacts your energy and the way you feel. Let’s say you observe 2 day fast benefits, and once you notice the positive results, you can create a solid plan for the upcoming months. The consistency of your plans matters, too.

Factors like your dietary choices during the fasting period and metabolic health can impact the outcomes of intermittent fasting on your blood sugar levels. Sticking with intermittent fasting over a few months might improve blood sugar control, but we don’t know the long-term effects. Improved blood sugar control could lower your chances of getting type 2 diabetes and other health problems related to how your body uses energy, but talk to your healthcare provider about how to safely achieve your goals.

Read more: Green Tea Intermittent Fasting: Benefits and Side Effects

does fasting lower blood sugar  

How Does Fasting Impact My Metabolism?

Glucose from carbohydrate intake serves as the primary energy source of our body. Once you have consumed a meal, carbohydrates are used for energy first. They are broken and delivered to the bloodstream, while the fats and any excess carbohydrates are stored for later usage. When you stop eating for a while, your body first uses the available carbohydrates for energy. After that, it breaks down stored fats, turning them into ketones for energy. Some protein will also be taken from muscle stores and turned into glucose to maintain a safe blood sugar level.

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An 18-Hour Fast May Be Just What Your Body Needs for Optimal Health

Ketones are another way our bodies get energy when we don’t have enough glucose. Fasting or eating very few carbs can make our bodies use ketones instead of sugar for energy. This switch from sugar to ketones is called metabolic switching, which is thought to provide some health benefits besides weight loss (7).

Note that when you lose weight, your metabolic rate can go down. This happens due to your body size and possibly muscle mass becoming smaller, as it takes less energy to maintain and carry around. However, this reduction in metabolic rate is not only associated with the loss of body size alone (4).

Some people opt for calorie restriction as an alternative to intermittent fasting. Severe calorie restriction over a long period can cause your metabolic rate to drop as your body enters what is sometimes called starvation mode (4). The scientific term for this is “adaptive thermogenesis.” Your body does this to conserve energy as a natural defense against organ failure or death from starvation.

Currently, limited research follows the long-term impact of intermittent fasting on metabolic rates. You must evaluate your fitness objectives before opting for any diet plan. Again, an expert’s insightful guidance could help you make the right choices.

How Long Does It Take to Lower Blood Sugar?

The time it takes to lower blood sugar depends on many factors. Here is a general overview of some of these factors:

  • Diet: A diet low in added sugar and high in nutrient-dense foods can have an instant and prolonged impact on blood sugar levels (3).
  • Medication: People who are taking diabetes medication may experience an immediate impact on their blood sugar levels. However, this depends on the dosage and type of medication (15).
  • Exercise: Regular physical activity can improve your insulin sensitivity. It may also help the muscles use glucose more effectively, lowering your blood sugar (2).
  • Health Status: Metabolic health includes factors like pancreatic function and insulin resistance. These influence how quickly blood sugar levels can be reduced.
See also
What Can You Drink During Intermittent Fasting?

Generally, a healthy lifestyle has been shown to create a much better impact on blood sugar levels than any other routine. In a major NIH-funded study, scientists followed over 3,200 men and women with prediabetes for three years (10).

  • One group made healthy lifestyle changes, like eating a low-calorie, high-fiber diet, exercising regularly, and losing a small amount of weight.
  • Another group took a diabetes medication called metformin.
  • The last group took a placebo (a fake pill).

The results were impressive: The group that made healthy lifestyle changes was 58% less likely to develop type 2 diabetes than the placebo group. For those over age 60, the risk reduction was even greater, at 71%. This shows that lifestyle changes can be a very effective way to prevent type 2 diabetes, especially for older adults.

One should talk to their healthcare provider to help them decide what lifestyle modifications to implement.

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does fasting lower blood sugar  


  • How can I flush sugar out of my system fast?

Remember that your body is designed to handle sugar fluctuations, so if you are healthy with no impaired glucose metabolism, you don’t need to worry about flushing sugar out of your system after eating a sugary or high carbohydrate meal. General ways to help support balanced blood sugar levels include eating a healthy, balanced, high fiber diet, drinking enough water, and exercising regularly. If you have diabetes or impaired glucose tolerance and think your blood sugar is too high, you should seek medical attention and discuss blood sugar management with your healthcare team. 

  • Why is blood sugar higher when fasting?

Blood sugar is maintained during fasting due to gluconeogenesis. The process occurs when one wants to maintain safe blood sugar levels, even when the food intake is low. The body turns other substances such as protein and glycerol into glucose to make sure that your blood sugar doesn’t become dangerously low. Gluconeogenesis should not cause your blood sugar to be abnormally high, however, so if you are experiencing hyperglycemia, you should see your healthcare provider.

  • What happens after 2 weeks of no sugar?

After two weeks of no added sugar, you may start experiencing positive changes in your body. Some people report that their energy levels become more consistent as a more balanced diet helps maintain steady blood sugar levels. You might find that your mind is clearer and you can focus better. You may probably crave sugary foods less. Your skin might improve with less acne and inflammation. Plus, you might lose weight if added sugar was a large contributor of calories to your diet.

  • What lowers blood sugar immediately?

Try a brisk walk or some other moderate exercise to bring your blood sugar down quickly. This helps because your muscles use sugar for energy. Drinking water can also help flush out extra sugar from your body. Please remember to take any other actions recommended by your healthcare provider.

The Bottom Line

Learning to maintain blood sugar while fasting takes time. Any type of fasting will change your blood sugar levels and how much insulin you produce. When you first start fasting, it is important to closely watch these levels to make sure your blood sugar stays within a healthy range. If you have impaired blood sugar control or take medications that affect your blood sugar, you will need to be monitored by a healthcare provider if you attempt any type of fasting. 

So the answer to one of the most-asked questions, “Does fasting lower blood sugar?” is yes. You should consult your healthcare team before opting for any eating or fasting plan. Create a meal plan for the days you will not be fasting. This helps ensure you consume enough food to keep your body going.


This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!


  1. A type of intermittent fasting reduces fluctuations in blood sugar levels (2023,
  2. Blood Glucose and Exercise (n.d.,
  3. Carbohydrates and Blood Sugar (n.d.,
  4. Changes in Energy Expenditure with Weight Gain and Weight Loss in Humans (2016,
  5. Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes (2018,
  6. Effect of Intermittent Fasting Diet on Glucose and Lipid Metabolism and Insulin Resistance in Patients with Impaired Glucose and Lipid Metabolism: A Systematic Review and Meta-Analysis (2022,
  7. Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting (2017,
  8. Low Blood Glucose (Hypoglycemia) (2021,
  9. Physiology, Fasting (2023,
  10. Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin (2002,
  11. Restructuring of the Gut Microbiome by Intermittent Fasting Prevents Retinopathy and Prolongs Survival in db/db Mice  (2018,
  12. Role of Minerals and Trace Elements in Diabetes and Insulin Resistance (2020,
  13. Sexual Dimorphism in Glucose and Lipid Metabolism during Fasting, Hypoglycemia, and Exercise (2015,
  14. The effects of intermittent compared to continuous energy restriction on glycaemic control in type 2 diabetes; a pragmatic pilot trial (2016,
  15. Type 2 diabetes: Learn More – What medications help in type 2 diabetes? (2023,


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