There Are Nine Potential Side Effects Of Intermittent Fasting, Including Intermittent Fasting Headache

intermittent fasting headache

intermittent fasting headache

Updated on 7/17/2024
Martin AlvarezBy Martin Alvarez
Nutritionist/Dietitian Professional Guide
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People call eating patterns that include regular periods of fasting in which they consume very few or no calories "intermittent fasting," and "intermittent fasting" describes those eating patterns.

Researchers Have Found That Intermittent Fasting May Have Several Positive Effects on Health, Including The Following:

intermittent fasting

intermittent fasting


  • Loss of weight
  • Reduced exposure to factors that can cause heart disease
  • Bring down your blood pressure.
  • Improved insulin sensitivity
  • Decrease in the levels of various markers of oxidative stress
  • Improved regulation of blood sugar levels

These Findings Have Contributed To The Rise In Popularity Of Various Intermittent Fasting Regimens, Including The Following:

Time-restricted feeding

Time-restricted feeding


You may be wondering if intermittent fasting could hurt your body if you're thinking of trying it out, but you're also curious about the potential adverse effects it might have on you.

The simple answer is that most people can safely practice intermittent fasting. Nevertheless, research has shown intermittent fasting is associated with a few mild adverse side effects. In addition, it is not the best option for everyone.

This Article Discusses Nine Possible Adverse Effects That May Be Brought on By Intermittent Fasting

 Effects That May Be Brought on By Intermittent Fasting

Effects That May Be Brought on By Intermittent Fasting

1. Starvation and Insatiable Appetite

The fact that hunger is one of the most common side effects associated with intermittent fasting may not come as much of a surprise to you.

If you cut back on the number of calories you consume or go for extended periods without eating, you might find that your hunger levels rise.

A group of participants in a study involving 112 people was randomly assigned to either a continuous or intermittent calorie restriction regimen. They did this for a year, eating either 400 or 600 calories on two days that were not consecutive each week.

Starvation and Insatiable Appetite

Starvation and Insatiable Appetite


These groups reported significantly higher levels of hunger than those who followed a low-calorie diet combined with ongoing calorie restriction.

According to the findings of various studies, one of the symptoms that people typically experience during the first few days of a fasting regimen is hunger.

One study conducted in 2020 examined 1,422 people who had participated in fasting regimens that ranged from 4 to 21 days in length. Only during the first few days of the regimens were they most likely to experience hunger symptoms.

As a result, symptoms such as hunger might disappear as your body gets used to going without food at regular intervals.

2. Ailments Such as Headaches and Dizziness

Ailments Such as Headaches and Dizziness

Ailments Such as Headaches and Dizziness


A common adverse effect of intermittent fasting is experiencing headaches. In most cases, they manifest themselves during the initial few days of the fasting protocol.

A review published in 2020 looked at the results of 18 studies that followed people on intermittent fasting regimens. Some people who participated in the four studies that found side effects found that they experienced intermittent fasting headaches.

It is interesting to note that researchers have discovered that "fasting headaches" typically manifest themselves in the frontal region of the brain and that their pain intensity is usually low to moderate.

In addition, those who suffer from headaches on a more regular basis are more likely to experience headaches during the fasting process than those who do not.

Researchers have hypothesized that headaches may be a side effect of intermittent fasting due to low blood sugar levels and the withdrawal from caffeine.

3. Digestive Issues

Digestive Issues

Digestive Issues


When you do intermittent fasting, you risk developing digestive issues such as constipation, diarrhea, nausea, and bloating. These symptoms are possible side effects of the practice.

The decreased amount of food you consume while following certain intermittent fasting routines may negatively impact your digestion, leading to constipation and other unwanted side effects. In addition, the changes in diet typically associated with periodic fasting programs can cause bloating and diarrhea.

Constipation can be made even worse by dehydration, which is another common side effect associated with intermittent fasting. When engaging in intermittent fasting, it is crucial to ensure that you maintain an adequate level of hydration at all times.

Choosing foods high in fiber and nutrients can help reduce the risk of constipation.

4. Irritability and Various Other Shifts in Mood

Irritability and Various Other Shifts in Mood

Irritability and Various Other Shifts in Mood


When someone engages in intermittent fasting, there is a possibility that they will experience irritability as well as other mood disturbances. If your blood sugar is low, you may experience irritability due to the condition.

In medical terminology, hypoglycemia refers to low blood sugar levels when a person restricts their calorie intake or fasts for an extended period. Because of this, one may experience irritability, anxiety, and difficulty concentrating.

The participants in a study conducted in 2016 found that they were significantly more irritable during an 18-hour fasting period than when they were not fasting—the survey of 52 women.

It was discovered by the researchers that, although the women reported feeling more irritable at the end of the fasting period, they also experienced a greater sense of accomplishment, pride, and self-control than they did when they reported feeling these things at the beginning of the fasting period.

5. Tiredness And A Lack Of Energy

Tiredness And A Lack Of Energy

Tiredness And A Lack Of Energy


According to studies, some people who practice various methods of intermittent fasting experience feelings of fatigue as well as low levels of energy.

The symptoms of fatigue and weakness can be brought on by low blood sugar, which can be brought on by intermittent fasting. Additionally, some people may experience sleep disruptions as a result of intermittent fasting, which can lead to feelings of fatigue during the day.

However, there is evidence from several studies that intermittent fasting can help reduce fatigue, particularly as the body becomes accustomed to the pattern of regular fasting periods.

6. Bad Breath

Bad Breath

Bad Breath


A decrease in salivary flow causes a reduction in salivary flow, and a decrease in salivary flow causes a subsequent increase in the concentration of acetone in the breath. Some people who participate in intermittent fasting can experience the unpleasant side effect of having bad breath because there is a decrease in salivary flow—saliva flow.

If you fast, your body is forced to rely on stored fat for energy to survive. Because acetone is a by-product of fat metabolism, you will notice an increase in its level in your blood and your breath while fasting.

Drinking plenty of water throughout the day is important to avoid this problem. Drinking plenty of water throughout the day will help you avoid this problem.

7. Sleep Disturbances

Sleep Disturbances

Sleep Disturbances


According to the findings of some studies, one of the most common adverse effects of intermittent fasting is disruptions in one's sleep, such as an inability to fall asleep or remain asleep once one does fall asleep.

A study conducted in 2020 observed 1,422 people who took part in fasting regimens that ranged from 4 to 21 days in length. According to the study's findings, 15 percent of participants reported experiencing sleep disruptions due to fasting, and they mentioned this aspect of the side effects more frequently than others.

Intermittent Fasting Sleep

Intermittent Fasting Sleep


Because your body is flushing out large quantities of salt and water through its kidneys during the first few days of an intermittent fasting routine, you may experience more fatigue than usual during those first few days. This can also result in low levels of salt in the body and dehydration.

On the other hand, the findings of other studies have shown that intermittent fasting has no impact on the quality of sleep.

A group of 31 obese people were recruited for a study in 2021 and asked to participate in an alternate-day fasting program while also adhering to a low-carb diet for six months. According to the study's findings, this treatment did not have any impact on the quality or duration of sleep or the degree of insomnia.

The results of yet another study from 2021 were the same.

8. Dehydration

Dehydration signs

Dehydration signs


As was stated, the first few days of fasting cause the body to expel significant quantities of water and salt through the urinary tract. This phenomenon is referred to as natural diuresis or the natriuresis that results from fasting.

You run the risk of becoming dehydrated if something like this takes place, and you don't make an effort to replace the fluids and electrolytes that you lost through urine.

In addition, individuals who engage in the practice of intermittent fasting might forget to drink, or they might not drink enough. When you start an irregular fasting routine, you may find that this occurs more frequently than usual.

Drink water frequently throughout the day and keep an eye on the shade of your urine to ensure you get enough fluids. The ideal hue for it would be something like a light lemonade. If your urine is dark in color, you may be dehydrated.

9. Malnutrition




Intermittent fasting can cause malnutrition if it is not carried out correctly.

If a person abstains from food for an extended period and fails to provide their body with an adequate supply of nutrients, they risk developing malnutrition. The same is true for diets that continuously restrict energy intake but are poorly planned.

People can typically satisfy their requirements for both calories and nutrients while participating in various intermittent fasting programs.

However, suppose you don't carefully plan or practice your fasting program over a long period or deliberately restrict the number of calories you consume to an extreme level. In that case, you risk developing malnutrition and other health complications.

Because of this, it is necessary to consume a balanced and nourishing diet while engaging in the practice of intermittent fasting. Be careful not to cut your calorie intake too drastically at any point.

Consult with a qualified medical professional who has prior experience with intermittent fasting. They will be able to assist you in developing a strategy that is risk-free and gives you the right amount of calories and nutrients for your body.

Who Should Stay Away From The Practice Of Intermittent Fasting?

Stay Away  Intermittent Fasting

Stay Away Intermittent Fasting


Some people may find that engaging in intermittent fasting is a wise decision, but for others, it is neither appropriate nor safe.

If someone engages in intermittent fasting, there is a possibility that they could develop potentially harmful side effects.

In general, healthcare professionals recommend that the following individuals avoid participating in intermittent fasting:

Women who are pregnant

Women who are pregnant


  • Women who are pregnant or who are nursing or chest-feeding their infants
  • children in their younger and teenage years
  • Adults over the age of 60 who struggle with weakness
  • Individuals who lack adequate immunity
  • People who are currently or have previously suffered from eating disorders
  • patients suffering from dementia
  • Individuals who have a previous history of traumatic brain injury or post-concussion syndrome
who have a previous history of traumatic brain injury

who have a previous history of traumatic brain injury


This is not a comprehensive list, and there are some notable exceptions. For instance, medical professionals have employed fasting as a treatment for epilepsy in pediatric patients.

It is essential to discuss the benefits and risks of intermittent fasting with a reputable healthcare professional, especially if you already have a medical condition or are currently taking medications for your situation.

Some people are more likely to experience adverse side effects from fasting; therefore, it is essential to determine whether or not intermittent fasting is the safe choice for your particular requirements.

In addition, if you practice intermittent fasting and find that it causes side effects that last for an extended period, this may indicate that it is not beneficial for your body. These potential adverse effects include, among others:

extreme hunger

extreme hunger


  • Extreme hunger
  • Nausea
  • Irritability
  • Headaches
  • Fatigue
  • Faintness

Stop doing the intermittent fasting program if it's making you feel terrible and find another approach.

Even though this method of eating has been linked to positive health effects, many other things can be done to improve one's health that does not involve fasting.

It is far more critical to manage stress, maintain a diet that is well-balanced and rich in nutrients, get an adequate amount of sleep, participate in regular physical activity, and keep active than it is to lose weight.

The Bottom Line

bottom line

bottom line


Numerous scientific studies have found a link between intermittent fasting and various positive health effects, including a reduction in the risk factors for cardiovascular disease, weight loss, improved control of blood sugar levels, and other advantages.

Studies have shown that people who practice intermittent fasting may experience side effects such as hunger, constipation, irritability, headaches, and bad breath. This is even though fasting is generally regarded as a safe practice.

In addition, some people are cautioned against engaging in intermittent fasting by medical professionals. People who are pregnant, those who are breastfeeding or chestfeeding, and those who have eating disorders fall into this category.

Suppose you are considering giving a dose for intermittent fasting but want to ensure that it is a good and healthy option for you and does not cause intermittent fasting headaches. In that case, you should speak to a doctor or other qualified medical professional first