Can Intermittent Fasting Cause Fatigue? 5 Energy Tips 2023!

Reviewed by Madison Turner, MPH & Health Education Specialist

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Can Intermittent Fasting Cause Fatigue
Intermittent fasting can cause fatigue. Photo: Shutterstock

The idea behind intermittent fasting is to give your body breaks from digestion by organizing your food intake into short eating periods with very long fasting periods between.

There are many approaches to intermittent fasting. Time-restricted eating involves dividing your day into a brief eating window and a long fasting period each day. Alternate-day fasting refers to severe calorie restriction on specific days. Periodic fasting can involve an occasional total fast, such as in religious observation.

If you’re thinking you may want to practice an intermittent fasting regimen, you should be aware of several potentially serious intermittent fasting side effects including headaches and digestive issues.

Can intermittent fasting cause fatigue? Absolutely! But you may be able to manage it with your doctor’s guidance and a few simple adjustments.

Can Intermittent Fasting Cause Fatigue?

Yes. Although intermittent periodic fasting fatigue can often be quite significant, the good news is that, for most people, it will resolve on its own once your body adjusts to your new routine.

In fact, some people report significant improvements in their energy levels and sleep quality once they have adjusted to intermittent fasting.

Intermittent Fasting Causes Fatigue

Unlike other approaches to weight loss, intermittent fasting restricts your calorie intake to specific times. Because it doesn’t forbid you from eating specific foods, it may be a more flexible approach for some people, but gives you similar results[1] to traditional weight loss regimens.

However, it can come with some very uncomfortable side effects. Intermittent fasting fatigue is frequently more severe than just feeling a little sluggish. There are many potential causes for extreme tiredness with intermittent fasting.


While adjusting to an intermittent fasting regimen, many people neglect their water intake. Remember that you can still drink water and non-caloric beverages during fasting!

Keeping your water intake high enough may help to stave off side effects like fatigue and headaches. However, drinking too much water without consuming electrolytes at the same time can throw off your electrolyte balance and lead to other problems.

While research suggests that intermittent fasting may not directly affect[2] the concentration of electrolytes in your blood, a number of factors may lead to problems with your electrolyte balance.[3]

If you take certain medications, have a history of disordered eating, or suffer from chronic medical problems including high blood pressure, be sure to consult with your doctor before trying intermittent fasting, as you may be more at risk for electrolyte problems from fasting.

Sleep Disruptions

Many people report better sleep and less fatigue after their body has adjusted to an intermittent fasting routine. However, during those first several weeks, it’s very common to struggle with poor sleep quality which can make you feel tired all day. If you feel hungry at bedtime, it can be hard to fall asleep and stay asleep.

Low Blood Sugar

Any dietary restriction can leave you struggling with low blood sugar. It can take time for your body to adjust to sudden changes in energy metabolism.

As your body learns to burn fat for energy during fasting times, your blood glucose levels will drop below normal. Over time, your body may accomplish better blood sugar control and improved insulin sensitivity, creating more stability[4] in your blood sugars and alleviating fatigue.

Low blood sugar during the adjustment period can lead to extreme fatigue, headaches, and discomfort.

Not Eating Enough Nutrients

Because you’re packing your entire food intake into just a few hours, or going long periods without eating, you may not get enough calories or micronutrients. Some people may resort to binge eating after a fast, consuming nutrient-poor high-energy foods rather than a well-balanced diet.

Other approaches to weight loss such as the Mediterranean diet may help you achieve your body weight goals without as much risk for nutrient deficiencies.

Intermittent Fasting Disadvantages

Some research indicates that intermittent fasting may benefit everything from the gut microbiome[5] to cognitive function.[6] However, intermittent fasting can negatively affect your energy levels and cause serious health problems for some people.

Beyond problems like malnutrition, headaches, lightheadedness, irritability, mood changes, and digestive issues like constipation, intermittent fasting may carry potentially serious health risks.

Some effects of intermittent fasting which are fine for one person may carry extreme risks for another. If you have a history of eating disorders, intermittent fasting may trigger relapse. People with health problems like diabetes should avoid intermittent fasting without guidance from a dietitian or physician because it could cause serious problems with their blood sugar.

Likewise, pregnant and nursing women should not fast.

If you have side effects like fasting headaches and fatigue that last beyond the adjustment period, stop intermittent fasting until you have consulted a physician.

5 Tips To Overcome Intermittent Fasting Fatigue

5 Tips To Overcome Intermittent Fasting Fatigue
Intermittent fasting fatigue is a common complaint. Photo: Shutterstock

Intermittent fasting fatigue is a common complaint, especially during the first weeks after making the change. Before considering intermittent fasting, be sure to consult with your doctor, as side effects can become serious for some people.

Fatigue associated with intermittent fasting can become severe. You may be able to reduce intermittent fasting fatigue by:

  • Stay hydrated
  • Take your vitamins
  • Eating enough food
  • Adjust balanced diet 
  • Prioritize sleep

Stay Hydrated

Many of us forget to drink water throughout the day. Without added hydration and electrolytes from regular meals, dehydration can be a major concern with intermittent fasting.

Be sure you’re staying hydrated, but don’t just chug gallons of water to help yourself feel full, either. Drinking too much water too fast without replacing electrolytes can lead to problems like water toxicity.[7] 

Drinking enough water (without overdoing it!) should be a priority while you’re fasting.

Take Your Vitamins

Taking a vitamin supplement can help you compensate for potential deficiencies. Even better news, many vitamins can help boost your energy and alleviate fatigue! The best vitamin for energy will be one that incorporates a full B-vitamin complex. Minerals like magnesium and fatty acids such as omegas may also help with energy and mood!

Eat Enough Food

It can be hard to eat enough for an entire day in just a few hours. Careful meal preparation in advance can help you get the calories you need during your eating windows.

If losing weight is your primary goal with intermittent fasting, cutting your calories too much too fast can actually do more harm than good. A slow, steady reduction in calories over time can lead to more sustainable weight loss.

Also, try to eat foods that will last in your system. Prioritizing healthy fats from foods like nuts, fatty fish, fiber from leafy greens and veggies, and complex carbohydrates from whole grains will prevent energy crashes and help equalize your energy metabolism by slowing down your digestion. This food list may help you incorporate the right foods for success.

Adjust Balanced Diet

Intermittent fasting might help you lose weight. However, skipping meals or going without food for several hours at a time isn’t all it takes for long-term, sustainable weight loss.

While intermittent fasting has been indicated as a potential treatment for metabolic syndrome, including decreasing obesity, it only works if you’re eating a well-balanced diet. But changing your entire way of life and your diet at the same time may be too much all at once.

Before you start intermittent fasting, take a good look at your regular diet. Making small, sustainable changes to your eating habits before you try intermittent fasting will make your adjustment period easier, avoid excessive strain on your body, and ensure better success while providing the many health benefits of a balanced diet.

Prioritize Sleep

Prioritize Sleep
You need to prioritize sleep while intermittent fasting. Photo: Shutterstock

Sleep disruptions from intermittent fasting can cause serious mental fatigue, leaving you dragging throughout the day. Especially while you’re letting your body adjust, dedicate extra time to rest and sleep.

Fasting can increase certain stress hormones in the body, especially at first, which will keep you awake. Some people benefit from taking a melatonin supplement while fasting, although melatonin absorption is better when taken with food.

Good sleep hygiene practices such as avoiding looking at screens, dim and warm lighting in the evening, and consistent routines for bedtime and wake time can all help as well.


If you’re considering an intermittent fasting plan, it’s essential to consult with your doctor first. While there may be some health benefits, people who practice intermittent fasting often experience significant challenges.

Extreme fatigue is common during the adjustment period when you’re starting intermittent fasting. However, it should subside over time.

Staying hydrated, getting enough vitamins and micronutrients, eating enough calories with a balanced diet, and prioritizing sleep may all help you manage intermittent fasting fatigue.

Frequently Asked Questions

Can intermittent fasting cause fatigue?

Yes! Low blood sugar, dehydration, sleep disruptions, and insufficient calories and nutrients can all cause fatigue during intermittent fasting.

Should I avoid intermittent fasting if I’m feeling fatigued?

Maybe. If your fatigue is unmanageable or lasts beyond the first few weeks of the adjustment period, you should stop intermittent fasting until you can talk to your doctor. Likewise, if you have risk factors for electrolyte imbalances or other health problems, the fatigue from intermittent fasting may indicate a serious issue.

What can I do to manage intermittent fasting fatigue?

Stay hydrated, take a high-quality vitamin-like Care/of, prioritize rest, be sure you’re eating a well-balanced diet, and talk to your doctor to rule out other complications.

+ 7 sources

MIDSS adheres to strict procurement guidelines and relies on peer-reviewed studies, academic research institutes, and medical associations. We work mainly with peer-reviewed studies to ensure the accuracy of the information. We avoid the use of tertiary references. You can read about how we ensure the accuracy and timeliness of our content in our editorial process.

  1. Tine Sundfør, Svendsen, M. and Tonstad, S. (2018). Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial. [online] 28(7), pp.698–706. doi:
  2. David Chibuike Ikwuka, Bond Anyaehie, Eghosa Iyare and Kelechi Ezeudensi (2021). Assessment of Hematological and Serum Electrolytes Effects of Intermittent Fasting on Mice. [online] ResearchGate. Available at:
  3. Isha Shrimanker and Bhattarai, S. (2023). Electrolytes. [online] Available at:,to%20high%20or%20low%20levels. 
  4. Yuan, X., Wang, J., Yang, S., Gao, M., Cao, L., Li, X., Hong, D., Tian, S. and Sun, C. (2022). 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. [online] 2022, pp.1–9. doi:
  5. Muhammad Nadeem Khan, Sidra Irshad Khan, Madeeha Ilyas Rana, Arshad Ayyaz, Muhammad Yousaf Khan and Imran, M. (2022). Intermittent fasting positively modulates human gut microbial diversity and ameliorates blood lipid profile. [online] 13. doi:
  6. Jip Gudden, Alejandro Arias Vasquez and Bloemendaal, M. (2021). The Effects of Intermittent Fasting on Brain and Cognitive Function. Nutrients, [online] 13(9), pp.3166–3166. doi:
  7. Yonemura, K., Akira Hishida, Miyajima, H., Kei Tawarahara, Mizoguchi, K., Nishimura, Y. and Kentaro Ohishi (1987). Water intoxication due to excessive water intake : Observation of initiation stage. Japanese Journal of Medicine, [online] 26(2), pp.249–252. doi:


Paige is a Certified Registered Dental Hygienist with extensive knowledge in patient education, nutritional intervention, and the impact of oral health on systemic disease. She is also a professional competitive athlete with a world championship title from the Arnold Fitness Championship in 2019.


Madison is a health and science consultant with experience in program planning and evaluation, qualitative research and analysis, marketing and communications, and individualized treatment planning. Whether you need a lab report proofread or a public health consult on a new project, Madison is the person for you! Madison is extremely goal-oriented, detailed, and focused.

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