10 Intermittent Fasting Side Effects That You Need To Know

Over the last several years, intermittent fasting has been increasingly popular for its underlying promises of weight control and enhanced health.

The premise is that deducting calories a few times every week and limiting meals to a shorter eating duration a day is simpler than deducting calories moderately in your every meal.

Extended periods of intermittent fasting beyond the usual time between meals have a lot of benefits.

It may change gene expression, increases levels of human growth hormone boosts cellular repair, and improves insulin sensitivity, in a way that promotes disease prevention and lifespan, according to proponents.

Intermittent Fasting Side Effects


Side Effects of Intermittent Fasting

Let’s have a look at some of the side effects of intermittent fasting:

  • Digestive Problems

    If you undertake intermittent fasting, you might encounter digestive difficulties such as bloating, diarrhea, constipation, and nausea.

    The reduced food intake associated with some intermittent fasting regimes could have a severe impact on your digestion, causing side effects, such as constipation.

    Furthermore, dietary modifications connected with intermittent fasting regimens could result in diarrhea and bloating.

    Constipation could be exacerbated by dehydration, which is another typical side effect of intermittent fasting.

    As a result, it is critical to stay properly hydrated while fasting intermittently. Constipation might be avoided by eating fiber-rich and nutrient-dense foods.

  • Hunger And Cravings

    Hunger is one of the most common negative effects of intermittent fasting, which comes as no surprise.

    You might experience greater hunger if you cut your calorie intake or go long periods without eating.

    Some 115 people were randomly allocated to an intermittent energy restriction group in a study. For a year, they ate 400 or 500 calories on two nonconsecutive days each week.

    These individuals reported feeling more hungry than those who followed a diet low in calories with constant restriction in the calorie intake.

    According to studies, hunger is a common symptom people experience during the first few days of a fasting program.

    In a 2020 study, 1426 participants took part in fasting regimes that lasted 5–20 days. Only during the first several days of the regimens did they suffer hunger sensations.

    As your body adjusts to regular fasting periods, sensations like hunger might fade away.

  • Headaches And Lightheadedness

    Intermittent fasting is often associated with headaches. They usually happen during the first few days of a fasting regimen.

    A study published in 2020 looked at 20 research patients who used intermittent fasting. Some participants reported moderate headaches in the four studies that recorded side effects.

    Researchers discovered that “fasting headaches” are commonly located in the frontal region of your brain, with pain that is moderate to mild in severity.

    Furthermore, persons who regularly suffer from headaches have a more likelihood of suffering from headaches while fasting than those who do not.

    Caffeine withdrawal and low blood sugar have been linked to headaches during intermittent fasting, according to studies.

  • Irritability And Mood Swings

    When an individual practices intermittent fasting, those individuals might experience mood swings, such as irritation.

    If your blood sugar is low, you could be more irritable. Low sugar in the blood, also known as hypoglycemia, might occur during times of fasting or calorie restriction. Poor focus, irritability, and anxiousness are possible outcomes.

    A 20-hour duration of intermittent fasting made participants much more irritable than a non fasting time, according to a 2015 study of 60 women.

    Interestingly, the researchers discovered that while the women were quite irritated towards the end of the intermittent fasting period, they also felt a greater sense of feeling of self-control, accomplishment, and pride than they did at the beginning.

  • Breath Problems 

    Bad breath is an unpleasant side effect that some people experience when they fast intermittently.

    An increase in acetone in the breath and lack of salivary flow cause this side effect. When you fast, your body burns fat for energy.

    As acetone is a byproduct of fat metabolism, it rises in your blood and breath while you fast.

    Dehydration, which is a sign of intermittent fasting, can also produce dry mouth, which might lead to foul breath.

  • Fatigue And Low Energy 

    Some people who practice different forms of intermittent fasting often report low energy and weariness, according to studies. Intermittent fasting could make you feel weak and fatigued due to low blood sugar.

    In addition, intermittent fasting might produce sleep disruptions in certain persons, resulting in fatigue during the day.

    However, some research suggests that intermittent fasting could help you feel less tired, especially as your body adjusts to regular fasting intervals.

  • Dehydration 

    The body discharges a lot of salt and water in your urine during the first few days of intermittent fasting. This is referred to as fasting natriuresis or natural diuresis.

    You could become very dehydrated if this occurs to you and you do not restore the electrolytes and fluids you lost through peeing.

    In addition, persons who practice intermittent fasting might drink insufficiently or forget to drink.

    This is especially right when you initially start an intermittent fasting program. Drink plenty of water throughout the day and keep an eye on the color of your urine.

    It should be the hue of pale lemonade. Dehydration might be indicated by dark-colored urine.

  • Disturbances In Sleep 

    According to some researchers, sleep difficulties, like the inability in falling asleep, are one of the very common negative side effects of intermittent fasting.

    In a 2020 study, 1500 participants engaged in fasting regimens ranging from 5 to 20 days. Fasting caused sleep disruptions among 20% of the subjects, according to the study.

    This was mentioned more often than different negative side effects. As your body excretes a lot of water and salt through your urine, fatigue might be more typical during the early days of an intermittent fasting diet. Low salt levels and dehydration are possible outcomes.

    Different research has found that intermittent fasting does not affect sleep. A study published in 2020 looked at 30 obese persons who fasted on alternate days while simultaneously eating a low-carb diet for six months.

    The study discovered that this regimen did not affect sleep duration, sleep quality, or the severity of insomnia.

  • Malnutrition 

    Intermittent fasting, if done incorrectly, might result in malnutrition. Malnutrition occurs when a person fasts for long periods and does not refill their body with necessary nutrients.

    The same could be said for unplanned long-term energy restriction diets. On various types of intermittent fasting programs, people might meet their nutrient and calorie needs.

    However, if you do not carefully follow or plan your intermittent fasting program over a lengthy period, or if you purposely restrict calories to an extreme level, you risk malnutrition and different health problems.

    That is why, during intermittent fasting, it is critical to eat a nutritional and well-balanced diet. Make sure you are not restricting your calorie intake too much.

    A health care expert with knowledge in intermittent fasting could assist you in developing a safe diet that provides you with the optimum number of nutrients and calories.

  • Low Blood Sugar Levels 

    If you have dizziness, chronic nausea, or headaches while on the intermittent fasting diet, it is a red flag that your blood sugar is out of control.

    Diabetics should avoid fasting diets. Hypoglycemia, a serious complication for anyone with thyroid or insulin issues, might be caused by intermittent fasting.

    Any intermittent fasting diet that requires you to forego breakfast might hurt your blood sugar level.

    Starting your day on an empty stomach might throw off your entire day and set you up for powerful desires later.


People are drawn to attempt intermittent fasting for weight loss since it is sustainable and allows them to eat their favorite meals.

Different advantages include reduced inflammation and illness prevention. Many people brag about a reduction in bloating and improved digestion. Another advantage could be better sleep, clearer skin, and improved mental clarity.

However, these benefits will not appear immediately, and many people will have to go through a period of adjustment, which might involve some unpleasant obstacles on the way.