Intermittent Fasting: 9 potential side effects

5-point Summary

• Intermittent Fasting (IF) has become increasingly popular in recent years as a way to improve health, lose weight, and increase longevity. IF involves alternating periods of eating and fasting, for example fasting for 16-hours a day (fasting window) and eating during the other 8-hours (eating window).  There are several potential benefits to IF including weight loss, improved insulin sensitivity, and decreased inflammation. But all of this only happens if you practice IF along with a structured diet plan. Simply not eating for 16 hours without a good plan can cause health issues. So it is important to be aware of intermittent fasting side effects.
• The most common side effects from IF include tiredness, low energy and headaches. This can happen during the initial days of starting IF as your body adapts to it, but it can also be an ongoing side effect if the overall diet is not balanced.
• This most obvious of the risks from IF is nutritional deficiencies, as when you aren’t eating, you aren’t consuming anything nutritious either for most of the day. This can give rise to deficiencies in essential vitamins and minerals such as iron and vitamin B12. To avoid this, it’s important to pay attention to nutrient intake during the eating periods of IF to ensure that you are getting enough nutrition. You should take a blood test if you are concerned or have any symptoms of such deficiencies and consult with a Doctor.
• Intermittent fasting can disrupt the body’s natural circadian rhythm, leading to insomnia and other sleep disturbances for some people. This is especially concerning for those who already struggle with sleep issues. Sleep is critical to health and ongoing sleep issues can give rise to other problems. If sleep issues persists, it might be worth it to stop IF, or at the very least, exploring alternative methods of sleep assistance such as supplementation etc.
• While there are many potential benefits to intermittent fasting, it’s important to be aware of the potential side effects too, particularly for certain populations like women and people with health conditions. It’s essential to pay attention to how your body responds to IF, and if you experience any negative side effects, it may be best to stop and consult with a nutritionist or Doctor for guidance.

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Intermittent fasting has become increasingly popular in recent years as a way to improve health, lose weight, and increase longevity. This type of eating pattern involves alternating periods of eating and fasting, typically for a certain number of hours each day.  There are several potential benefits to intermittent fasting, including weight loss, improved insulin sensitivity, and decreased inflammation. But there are intermittent fasting side effects too.

This is why we guide many people who are part of the Daily9 weight loss program to do intermittent fasting in a safe and effective manner. However, it’s important to note that like any dietary intervention, there are potential intermittent fasting side effects that should be considered before starting this type of eating pattern. This is especially true if you are trying it yourself without any guidance from a qualified nutritionist.

This holds especially true for certain populations, particularly adolescents, pregnant women, individuals with pre-existing eating disorders, and individuals who are medically underweight. 

In this article, we’ll be explaining in detail the potential intermittent fasting side effects that you should be aware of before embarking on such a practice. 

9 potential Intermittent Fasting side effects

Fatigue and Lethargy 

One potential intermittent fasting side effect is a decrease in energy levels, fatigue, and lethargy. When the body is in a fasted state, it is not receiving its usual energy source of food which can ultimately make it difficult to maintain energy levels throughout the day. 

This is especially true for those who are already struggling with fatigue or low energy levels. The initial transition to a fasted state may be difficult, both mentally and physically, in large part due to the adjustment period the body and its systems go through when starting to fast.

While this fatigue is likely to pass once adjusted, it’s important to proceed with caution, ensuring proper hydration and avoiding overexertion.

Loss of Muscle Mass

Another potential side effect of intermittent fasting is a decrease in muscle mass. While this isn’t typically of grand concern due to the fact that such a practice is, as presumed from its name, intermittent and temporary, it’s still worth noting. 

When the body finds itself in a fasted state, it’s likely to break down muscle tissue for energy depending on the duration of the fast. 

This is particularly concerning for athletes and those who engage in regular strength training or individuals who simply desire a more muscular frame. While it’s not a great risk and can, in fact, help reduce fat which improves the appearance of muscle, it’s important to ensure that any caloric restriction during intermittent fasting is matched by an increase in protein intake during the eating window. 

Headaches and Migraines

Headaches are also a common side effect of intermittent fasting. While this is likely due to dehydration in most cases, it may also be related to a change in blood sugar levels or a shift in certain neurotransmitters in the brain. 

During any given period of fasting, blood sugar levels are likely to drop. This can lead to headaches, migraines, or lightheadedness. This is especially concerning for those who are diabetic or have a history of low blood sugar. 

In order to mitigate this risk, it’s important to pay attention to blood sugar levels during a period of intermittent fasting and to eat a small snack if blood sugar levels drop too low. Not to mention the importance of consuming sufficient amounts of water throughout. 

Increase in Cortisol and Stress

A fourth potential side effect of intermittent fasting is an increase in the stress hormone cortisol. Fasting inevitably triggers the release of cortisol which can lead to feelings of stress and anxiety, not to mention feelings of irritability and a downturn in overall mood. 

This may be especially concerning for those who are already prone to stress, depression, anxiety, or other extreme mood swings. If this sounds like you, it’s important to pay attention to how you feel during intermittent fasting and stop if it’s causing you unnecessary stress.

If you’re not prone to such mental turbulence, simply expect your mood to diminish throughout a period of fasting. However, understand that this will be temporary.

Also Read: The Right Way To Do Intermittent Fasting

Risk of Developing Eating Disorders 

Another potential side effect of intermittent fasting is an increased risk of disordered eating, whether overeating, under-eating, binge eating, or otherwise. Though not a risk for everyone, for some people, intermittent fasting can trigger a preoccupation with food and an obsession with sticking to the eating schedule. 

Evidently, this can lead to disordered eating patterns such as restrictive eating or binge eating. To mitigate this risk, it’s important to be aware of your own history of disordered eating and to be mindful of how you feel during intermittent fasting.

If you feel uncertain in any way, don’t hesitate to consult with your doctor or nutritionist before embarking on any such journey and proceed under their supervision until you are comfortable with the process. 

Risk of Nutritional Deficiencies 

A sixth potential intermittent side effect is an increased risk of nutrient deficiencies. This is arguably amongst the most obvious of the risks, as when you aren’t eating, you aren’t consuming anything nutritious either.

As a result of being in a prolonged fasted state and failing to replenish your body afterward, deficiencies in essential vitamins and minerals can develop such as iron and vitamin B12. To mitigate this risk, it’s important to pay attention to nutrient intake during the eating periods of intermittent fasting and take a blood test if you are concerned or have any symptoms of such deficiencies.

Risk of Developing Gallstones 

A seventh potential side effect of intermittent fasting is an increased risk of gallstones. When the body is in a fasted state, it may produce more cholesterol, which can lead to the formation of gallstones. This is especially concerning for those who are already at a higher risk of gallstones. To mitigate this risk, it’s important to be mindful of cholesterol intake during the eating periods of intermittent fasting.

Also read:  Does Intermittent Fasting Boost Metabolism?

Sleep Disruption 

Arguably the most annoying side effect of intermittent fasting is the disturbance of sleep. Evidence strongly suggests sleep as one of the primary pillars of health; a disturbance to it can result in a variety of health concerns.

Intermittent fasting can disrupt the body’s natural circadian rhythm, leading to insomnia and other sleep disturbances. This is especially concerning for those who already struggle with sleep issues.

If you find yourself having trouble with sleep for a prolonged period of time whilst intermittent fasting, such a practice might just be the primary cause. In such a case, it might be worth it to consider eliminating the practice from your regimen, or at the very least, exploring alternative methods of sleep assistance such as supplementation or otherwise. 

Increased Risk of Hypoglycemia 

Finally, a prevalent risk and potential side effect of intermittent fasting is an increased risk of hypoglycemia or low blood sugar. 

When the body is in a fasted state, it may not have enough glucose to properly fuel the brain and body, which can lead to symptoms of dizziness, weakness, and confusion. This is especially concerning for those who are diabetic or have a history of hypoglycemia. 

For those who experience or who are at risk of such a side effect, it’s important to proactively monitor blood sugar levels during intermittent fasting and to eat a small snack if blood sugar levels drop too low. It goes without saying, consult with your medical doctor before proceeding with a fasting practice if you’re at risk of such a side effect. 

A Final Word on intermittent fasting side effects

While there are many potential benefits to intermittent fasting, it’s important to be aware of the potential intermittent fasting side effects, particularly for certain populations. It’s essential to pay attention to how your body responds to intermittent fasting, and if you experience any negative side effects, it may be best to stop and consult with a healthcare professional or halt the practice altogether. 

If you decide to proceed with an intermittent fasting regimen, It’s important to ensure that any caloric restriction during intermittent fasting is matched by an increase in nutrient-dense foods to mitigate the risk of nutrient deficiencies. 

Remember, what works for one person may not work for another, so it is crucial to find a diet that works for you and your body.

About the Author

Coach Shivani

Shivani is a Precision Nutrition-Certified Nutrition Coach with experience of coaching thousands of women. As a mom of two, Shivani knows what it takes for women to achieve weight loss & a healthy lifestyle through diet, exercise & sleep habits. She dislikes one-size-fits-all type advice.