8 Major Intermittent Fasting Side Effects That are Rarely Known

Intermittent Fasting Side Effects – Overview

People use the term intermittent fasting to describe eating behaviors that include frequent periods of fasting during which they consume extremely little or no calories.

Intermittent fasting has grown in popularity over the last few years due to its health benefits and weight loss promises.

A report shows that around 9% of the respondents indulged in intermittent fasting in 2019, which is higher than a few other diets.

The idea is that cutting calories drastically a few times a week or limiting meals to a shorter “eating window” each day is more straightforward than cutting calories moderately at every meal.

Extending fasting periods (beyond the regular time between meals) may help

Improving insulin sensitivity,

Boosting cell repair,

Changing gene expression,

They increase growth hormone levels to promote lifespan and disease prevention.

Does Intermittent Fasting Come With Side Effects?

Before considering the risks of intermittent fasting, remember that there are various types, and proof of their long-term effectiveness and safety is lacking.

However, the following are the most prevalent types:

  • Alternate day fasting (or ADF fasting): It is a type of fasting that asks you to fast every other day.
  • Modified alternate-day fasting: You must consume only 25% of your regular intake every other day.
  • Periodic fasting: In this fasting, you must restrict your food intake to 500-600 calories daily for 2 days per week.
  • Time-restricted eating: You must restrict your “eating window” daily.

Intermittent fasting also has several side effects that you must consider before undertaking this plan. Let’s talk about it further down.

8 Major Intermittent Fasting Side Effects

You may notice specific changes in your body and digestion right away. Although specific adverse effects may be milder, it’s still vital to be aware of them.

Several warning symptoms may appear sooner or later during intermittent fasting. Let’s discuss different types of intermittent fasting side effects. 

1. Overeating

When deprived of meals, your appetite hormones and hunger center in your brain go into overdrive. Hence, there is a significant biological push to overeat during fasting periods.

Two typical side effects of calorie-restricted diets come under intermittent fasting side effects—slowed metabolism and increased appetite.

These are just as probable when people practice intermittent fasting as when they decrease calories every day, according to a 2018 study.

The evidence is based on studies of time-restricted eating, indicating food that is out of sync with a person’s circadian rhythm (their body’s natural daily routine) can lead to metabolic issues.

2. Fatigue

Have you ever woken up in the middle of the morning yawning uncontrollably, only to realize you didn’t eat breakfast? Most people do intermittent fasting by skipping breakfast.

When you’re constantly tired or making stupid mistakes because of brain fog, it is a sign that you’re not consuming the correct meals during non-fasting hours or that fasting isn’t working for you.

3. Low blood sugar

Having persistent headaches, nausea, or dizziness during intermittent fasting is not a good sign for your health. It may often be that fasting is affecting your blood sugar levels.

Hence, it’s especially suggested that people with diabetes shouldn’t go for intermittent fasting as it may not benefit them. Instead, it will lead them to have affected blood sugar.

4. Digestive issues

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

The reduced food intake that various intermittent fasting regimes entail may severely impact your digestion, resulting in constipation and other unpleasant side effects.

Additionally, dietary modifications connected with intermittent fasting regimens might result in bloating and diarrhea.

Dehydration can exacerbate constipation, another typical side effect of intermittent fasting. As a result, it’s critical to stay hydrated adequately while fasting intermittently.

5. Mood Changes

When people practice intermittent fasting, they may experience irritation and other mood swings. For example, you may become irritable when your blood sugar levels are low.

Hypoglycemia, or low blood sugar, can occur during calorie restriction or fasting. Irritability, anxiousness, and poor focus are all possible outcomes.

6. Hormonal Imbalance

Those who already live an active lifestyle or were lean before fasting may have a hormonal imbalance due to this eating pattern.

In addition, intermittent fasting can induce irregular menstrual periods in women and other reproductive issues.

Sleeplessness increases stress, and thyroid difficulties can be symptoms of hormonal imbalances.

7. Sleep Issues

According to some studies, one of the most prevalent adverse effects of intermittent fasting is sleep difficulties, such as the inability to fall or stay asleep.

In research published in 2020, 1,422 participants fasted for 4–21 days. According to the study, fasting was linked to sleep disruptions in 15% of the subjects.

This was mentioned more than any other symptom.

Because your body excretes vast amounts of salt and water through urine in the early days of an intermittent fasting diet, It’s more likely to fatigue. It can lead to dehydration and a lack of salt.

8. Dehydration

As previously stated, the body discharges much water and salt in the urine during the first few days of fasting.

Natural diuresis, also known as fasting natriuresis, is the name given to this process. You could become dehydrated if this happens and you don’t restore the fluids and electrolytes you lost through pee.

In addition, those who practice intermittent fasting may forget to drink or drink insufficiently. This is especially true when you start on an intermittent fasting program.

Who Should Avoid Intermittent Fasting?

Intermittent fasting may be good for some people, but it isn’t suitable or safe for others. We have already mentioned the intermittent fasting side effects.

Intermittent fasting should be avoided for the following reasons, according to experts:

  • Older people who are experiencing frailty
  • Immunocompromised individuals
  • People who are pregnant or who are breastfeeding/chest-feeding small children or teenagers
  • Persons with dementia who are currently or have previously struggled with eating problems
  • Those who have had a catastrophic brain injury or have suffered from post-concussive syndrome


Fasting can be a beneficial complement to any healthy lifestyle, and most people can safely and efficiently include it in their daily routine.

However, before you start, ensure you’re informed about the side effects of intermittent fasting.

Overall, you can share your point of view or experience of intermittent fasting in the comment section. 

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