9 Common Negative Effects Of Intermittent Fasting (and How To Fix Them)

  • Post last modified:July 22, 2021
  • Reading time:20 mins read
  • Post comments:0 Comments

With various benefits such as losing weight, reducing inflammation, improving digestion, the possibility of a longer life, and so on, intermittent fasting has become more popular all over the world. 

However, before you start, you need to understand that nothing is perfect. There are always some flaws, no matter how good it looks. 

Intermittent fasting is no different. It has some negative effects as well.

Negative Effects Of Intermittent Fasting

For most of us who are accustomed to the traditional way of eating three meals a day, our body will take some time to adapt to extreme changes.

Just like the person who sits on the sofa all day, you can’t ask him to participate in a triathlon, right?

Therefore, when you start to reduce the number of meals and do not eat for longer periods of time, your body will naturally have some adverse reactions.

It can be uncomfortable, especially in the early stage of fasting. The good news is that as long as you endure the first week or two, you will soon begin to enjoy all the benefits it brings you.

As long as you know how to deal with these adverse reactions, you can get through the adaptation period more smoothly.

Before reading further, I would like to remind you again that intermittent fasting is not for everyone.

People who are in these situations should avoid any extreme diet change:

  • pregnant and breastfeeding
  • underweight
  • at or under the age of 18
  • elderly people
  • people with a history of eating disorders 
  • people with diabetes

It is always recommended to first consult a doctor before starting intermittent fasting, especially if you have any health issues.

Now, let’s take a look at the possible adverse effects during intermittent fasting: 

1. Hunger

Your body has always been accustomed to three meals a day, plus possibly some afternoon tea and various snacks. 

Your biological clock will signal your brain when it is time to eat. Eating is something you have always taken for granted.

What makes you feel hungry is a hunger hormone released by the body called ghrelin. This hormone has the effect of regulating appetite and usually peaks at breakfast, lunch, and dinner time. [*].

When you fast for the first time, ghrelin will not slow down the release rate immediately, so its level will continue to reach its peak, and make you feel hungry.

The first few days require strong willpower to overcome your hunger urges. However, during this process, you will encounter a certain critical point, after which the feeling of hunger will slowly subside.

You may have experienced this. In long-distance running or endurance training, when you reach a certain critical point, your body will feel extremely tired, making it very difficult to continue. However, if you hold on and fight through, you will feel more and more relaxed. 

How to overcome hunger in the early stage of fasting

Nutrition and cardiologist Dr. Luiza Petre suggests that drinking plenty of water every day for the first week or two can help you feel fuller and suppress the urge to stuff your mouth.

Drinking a glass of warm water every morning will thin your blood and remove toxins from your body. This also helps to control your appetite.

Through intermittent fasting, you will understand more deeply what the real feeling of hunger is. Many times, when you are craving, you are not hungry but only thirsty, or simply just bored.

In addition, drinking black coffee and green tea is also useful. However, one must be careful not to drink them at night. Otherwise, it could affect your sleep. Lack of sleep is another trigger of craving.

Other strategies are:

  • Stay as busy as possible during the day.
  • Avoid strenuous exercise.
  • Ensure balanced nutrition. Eat enough protein and healthy fats to prolong the feeling of fullness.

2. Craving for certain foods

Another side effect during intermittent fasting is a stronger appetite for certain foods, such as sweets, rice, noodles and other refined carbohydrates.

This is because your brain is used to using glucose as fuel. After your body has completely consumed the stored glycogen, your brain will send a signal to your body to find more sugar for energy.


You can easily satisfy your food cravings by choosing a more nutritious option.

Here are some alternatives for the most common foods that people crave:

  • Potato chips: Replace them with a salty snack that is higher in healthy fats and protein, such as nuts. Popcorn is also a good option.
  • Sweets:  Whole fruits such as apples, oranges, cherries, or melon will satisfy your sugar craving.
  • Chocolate:  Craving chocolate could be a sign of a magnesium deficiency. Eating magnesium-rich foods such as almonds may satisfy you and help with this deficiency. However, if you still can’t shake the chocolate craving, you should always seek dark, milk-free chocolate that contains at least 70 percent cocoa.

3. Headaches

While your body is adapting to a new diet, you could experience different degrees of headaches.

Low blood sugar causes headaches for many people, especially if you eat too many carbohydrates in a meal before fasting. This may cause your blood sugar to spike quickly, then drop rapidly after fasting, which may cause headaches.

Therefore, eating a low-carb diet before fasting can prevent this adverse reaction.

In addition, a lack of electrolytes could be another reason.

In the early stage of fasting, since you need to drink a lot of water to reduce hunger, the frequency of urination increases, which can excrete electrolytes in the urine.


⬥Eating foods rich in electrolytes and minerals can help prevent a lack of electrolytes. Additionally, you can simply add Himalayan Sea Salt into your water.

4. Tiredness

For most people, carbohydrates from food are the main source of energy for one’s body and brain. .

When you are eating all day, your blood sugar rises and falls like a roller coaster. When blood sugar collapses, it can take away your energy.

If you let your body rest for 16 hours, without eating anything during that time, your body will begin to use the stored fat to gain energy.

The energy conversion process takes a certain amount of time. You may feel tired and lack energy, especially during the first week or two of intermittent fasting.


  • drink plenty of water
  • replenish electrolytes
  • ensure adequate sleep

Once your body adapts to the new way of energy supply, it will give you more energy at full capacity. From then on, you will enjoy all the benefits of intermittent fasting such as a clearer mind, agile thinking, weight loss, and more.

From my experience, before I started my low-carb diet and intermittent fasting, I always felt sleepy in the afternoon and had to take a nap. Otherwise, I wouldn’t be able to focus on any tasks. Now it’s the exact opposite. I can maintain my vigorous energy all day long without tiredness.

You might be interested:

What Is The One Meal A Day Diet Plan

What Is The One Meal A Day Diet Plan?

The one meal a day diet plan can help your body convert to burn fat as a source of energy and achieve the goal of weight loss more quickly.

Read More

5. Irritability

Every method of intermittent fasting could have an impact on your mood in the first few weeks.

When you start intermittent fasting, your body is running on sugar fuel initially. As your body gets used to the new diet, it will switch over to fat burning.

Every time you eat, your insulin spikes. When you run out of stored sugar (also known as glycogen), you can feel fatigued, irritability, and may develop a headache.


I recommend combining intermittent fasting with a low-carb diet such as a ketogenic diet, or a low-carb Mediterranean diet. Also;

  • drink plenty of water
  • eat more vegetables
  • eat more healthy fats
  • get at least 7-8 hours of sleep

In addition, begin with 3 meals a day first. Maybe you can cut out the snacks initially. Then reduce to 2 or 1 meal a day. Whatever your body is most comfortable with. In this way, your body will gradually adopt the new schedule.

6. Digestive problems

During fasting, some people may experience some digestive symptoms.  

Your stomach produces gastric acid, to help digest food. Therefore, you may feel heartburn when you are not eating.

Other symptoms of indigestion may include nausea, hiccups, bloating, and constipation.


Usually eating more vegetables, drinking more water, and consuming less spicy foods can alleviate the discomfort.

Also, it is necessary to gradually extend the fasting period and avoid prolonged fasting.

If symptoms recur and persist, stop fasting, and seek medical attention as soon as possible. As previously stated, It is a good idea to speak with your doctor before beginning any changes to your diet.

7. Feeling cold

Cold fingers and toes while fasting is pretty common. Some people will get used to it quickly, while for others, it may take some time before they feel more comfortable.

There are many reasons for this feeling.

First of all, after you eat, your body will produce heat during the process of digestion. However, when you fast, because there is no food to digest, there will be no “central heating” treatment.

Secondly, your body is very good at protecting your vital organs, which means that if you don’t eat that much, your body will give priority to heating the organs and cooling down your limbs (hands and feet).

The good news is that your body actually burns calories to maintain a stable temperature.


  • You can warm your body by drinking hot water, hot tea, taking a hot bath, etc.

8. Overeating

This is another issue that most people encounter, including me.

Compensation is the first reason. You may feel that since you won’t be eating again for several hours, you can eat as much as you want after fasting.

Another reason is that you don’t eat enough calories for metabolism, or nutrition is not comprehensive, which results in a strong sense of hunger during fasting. Once it is time to eat, controlling your appetite may not be that easy.


Try drinking a glass of water or some apple cider vinegar. Doing this half an hour before meals can help reduce your appetite.

When eating, ensure to have various foods, including vegetables, protein, and healthy fats. Pay special attention to eating enough calories, but be careful not to overeat.

You can use this online tool to calculate the calories your body needs.

9. Frequent urination

You should have already learned that drinking more water is one of the most important ways to relieve the discomfort of fasting.

If you drink too much water, you will naturally go to the toilet more.

Unfortunately, there is no way to solve this problem. You can view this as exercise and be active a few more times a day.

Again, don’t forget to increase electrolyte intake in your diet.

Final Thoughts:

Intermittent fasting is an effective way to lose weight. It also can help one’s body fight inflammation, lower blood sugar, anti-aging, and improve overall health.

However, intermittent fasting has some negative effects and is not suitable for everyone. If you have any health conditions, or in general, please consult your doctor before starting any new diet.

Most people may experience some discomfort in the early stage of fasting. This is a normal reaction of the body in the process of converting energy metabolism.

You can relieve symptoms with the following tips:

  • Drinking plenty of water.
  • Supplementing the necessary nutrients such as electrolytes, protein, and fat. 
  • Get enough sleep. 
  • Avoiding strenuous exercise.

I recommend that you extend the fasting window gradually. It will not take long for your body to adapt, and these adverse reactions will disappear over time. After that, you will benefit from intermittent fasting in many ways.

Leave a Reply