5 Common Intermittent Fasting Side Effects to Expect

Intermittent fasting is awesome. Multiple research studies prove that it’s among the most powerful ways to shed pounds, improve heart health and reduce cancer risk, among other benefits. 

However, like any other health and fitness regimen, IF has its “not-so-good” side. In this post, we’ll be taking you through the five most common side effects people experience when they start intermittent fasting. You’ll learn what causes these side effects of intermittent fasting and how to avoid them. 

Potential Intermittent Side Effects


Hunger can be an unpleasant experience when you start intermittent fasting. But it’s a part of any regimen that involves going for prolonged periods without food, and it’s nothing to worry about. Plus, riding the hunger wave is possible when you understand what drives it.  

Hunger is a conditioned response to an empty stomach, usual mealtimes, and emotions like stress and boredom. Environmental factors, such as the smell and sight of food, can also cause hunger. 

The good news is that “learned eating times” can be reconditioned. That “I must eat now” feeling may linger for some days, but its effect will slowly subside as the body gets used to new feeding times.  

One way of dealing with hunger when you’re just starting intermittent fasting is to start with a reasonably simple approach, like 12-hour intermittent fasting. This approach is less restrictive than the 20:4 and Alternate Day IF methods but still promotes weight loss. 

Another idea is to move your meals a little later. For instance, instead of eating breakfast at six at home, how about having it later at work? But in the case of overnight fasting, you’ll want to have dinner a little earlier than usual.

And, of course, you want to avoid hanging around good-smelling food during your non-eating window.  Your olfactory sense is at its peak when fasting. Being around food will only make things difficult for you. 

Acid Reflux

You have probably heard or read that intermittent fasting can help improve the symptoms of gastroesophageal reflux disease (GERD). Several studies suggest intermittent fasting improves heartburn symptoms by mildly reducing acid exposure.

However, it’s also important to note that fasting can cause or aggravate acidity. Acidity or heartburn is a common side effect that most people report when they start doing IF.

Intermittent fasting is likely to cause acidity because of too much acid in an empty stomach. Because there’s no food to neutralize the acid, the acid may creep up, causing a burning feeling in your chest and throat. 

Luckily, when intermittent fasting, acid reflux tends to subside as the body gets used to the new eating pattern.

Here are several ways of dealing with acidity when fasting; 

  • Drink small quantities of water throughout the day (preferably warm water)
  • Get some exercise to help distract the body from hunger
  • Avoid spicy, sour, and high-fat foods when breaking the fast
  • Don’t overeat during mealtimes


Intermittent fasting can impact your sleep both positively and negatively. On the one hand, some people find that intermittent fasting improves their sleep by reducing the number of times they wake up at night. This could be due to improved circadian rhythms and reduced acid reflux, among other reasons. 

On the other hand, it’s common for intermittent fasting to disturb some people’s sleep. Intermittent fasting can cause insomnia by disrupting the circadian rhythm and triggering a spike in cortisol, the stress hormone. The dreaded experience of going to bed hungry may also cause a reduction in melatonin production- the hormone that promotes sleep. 

The good news is that insomnia due to intermittent fasting is typically temporary. After adjusting to the new routine (typically takes 2-4 weeks), you may start reaping the benefits of intermittent fasting for sleep. 

So, how can you combat insomnia when intermittent fasting? Start by experimenting with different fasting approaches and identify how each affects the quality and duration of your sleep. Secondly, schedule your last meal of the day 2-3 hours before bedtime so your body can properly digest it and reduce the risk of heartburn. 

Feeling Cold

Low body temperature is one of those intermittent fasting side effects that aren’t discussed much. That’s probably because it doesn’t affect everyone.

Don’t be alarmed if you get cold when doing IF or regular fasting. It’s normal and only lasts a short time. 

There are several reasons why intermittent fasting could make you feel chilly, the most obvious being reduced core body temperature. When you reduce food intake, your body typically goes into conservation mode. But this usually happens during the transition phase, meaning you won’t experience it long-term. 

Taking a break from food also means temporarily halting digestion. This means losing out on the heat produced during metabolism (a.k.a thermogenic response). 

There are several ways of warming when intermittent fasting, including wearing warm clothes, taking a hot shower and doing low-intensity exercises. Eating plenty of healthy fats and nutrients during your eating window is also advisable. 


There is evidence that intermittent fasting can cause constipation. This is when you have infrequent and uncomfortable bowel movements. 

Intermittent fasting-induced constipation typically occurs due to dehydration and failure to consume enough fiber. You typically get around 20% of your daily water intake from the food you take and the rest from drinks.

When you forget to drink enough water when doing IF, your large intestine absorbs most of the water in your stool. The result is a hard and dry stool that can obviously cause problems when going number two. 

On the other hand, dietary fiber softens the stool and makes it bulky. Larger, softer stools are easier to push out. 

Dealing with constipation when intermittent fasting is straightforward: increase your fiber intake and drink enough water.

It’s understandable if plain water doesn’t inspire you. Luckily, other calorie-free drinks like herbal teas, seltzer, and diluted apple cider vinegar are all allowed and won’t break your fast. 

Disclaimer: These IF side effects may not affect everyone the same way. Depending on your personality, lifestyle, and preferred intermittent fasting method, you may experience some or all of them. 

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