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If you Depend on Fasting to Lose Weight, Be Aware of Harmful Side Effects

A fit and healthy body is what we aspire to have. But for most of us, a healthy body means a lean and thin figure. In the present world, when everyone is in awe of 6-pack abs and a size zero body, we want to shed the fat as soon as possible, and we feel that fasting is the easiest way to achieve this. One such fasting pattern which has become a cult now is intermittent fasting. The support for intermittent fasting is incredible, and many people have become ardent followers of it. Intermittent fasting is a pattern of eating with regular periods of fasting during which a person consumes zero to no calories.


Many studies have claimed several benefits of intermittent fasting, including but not limited to:

  • Loss of weight
  • Reduced risk of heart disease
  • Reduce blood pressure
  • Improves insulin sensitivity
  • Reduction in oxidative stress-causing factors
  • Improved control of blood sugar levels


Several forms of intermittent are popular these days, such as:

  • TRF or Time-restricted feeding
  • ADF or Alternate-day fasting
  • PF or Periodic fasting


Before trying out intermittent fasting, we should have a clear understanding of its side effects as well. Though intermittent fasting is safe for most people, it is a strict no-no for some people.


Side effects of the intermittent fasting


The following are the potential side effects of intermittent fasting:


Increased appetite and craving for food

Yes, it is true. Hunger can be a side effect of intermittent fasting. When you have long periods of fasting without taking calories, you may feel a sudden increase in your appetite. According to a study published in the National Medicine of Library, intermittent energy restrictions cause higher hunger scores. But according to one more study, people tend to experience these hunger symptoms only for the first few days of intermittent fasting. So your body may adapt to intermittent fasting after the first few days.



Our body takes some days to adapt to intermittent fasting. Headache may be a common side effect during the first few days. These headaches may be due to low blood glucose levels and caffeine withdrawal during fasting.


Trouble with digestion

If you are doing intermittent fasting, you may face some digestive issues, such as:

  • Constipation
  • Diarrhea
  • Dehydration
  • Nausea
  • Bloating

Dehydration is a common side effect associated with intermittent fasting. Dehydration can induce constipation. Therefore, while practicing intermittent fasting, it is essential to drink plenty of liquids. In addition to it, choose a fiber-rich diet to relieve constipation.


Mood disturbances

Irritability and mood swings may affect your day while practicing intermittent fasting. A low blood sugar level can make you feel irritated and anxious. It may become difficult for you to concentrate for long hours.

Though you may become irritable during intermittent fasting, these days of struggle always follow a feeling of achievement and pride when you achieve your goals.



According to a review article published in the National Library of Medicine, intermittent fasting can cause bouts of low energy levels and fatigue. Low blood sugar levels due to prolonged fasting periods also make you feel weak and disturbed sleeping.
But the feeling of fatigue subsides when your body adapts to intermittent fasting.


Bad breath

Halitosis or bad breath is a common side effect in people following intermittent fasting. Fasting may cause a decreased salivary flow and increased acetone level in breath, causing bad breath. When you fast, your body uses fat as fuel and produces acetone as a by-product. You may also experience bad breath due to dehydration (again, a symptom of fasting) leading to a bad breath.


Abnormal Sleep

Intermittent fasting may cause disturbed sleep. You may either find it difficult to stay asleep or fall asleep. According to a study, sleep disturbances may happen more frequently than other side effects. Similar to other side effects, sleep disturbance is more common in the initial days and gradually decreases with time.



Intermittent fasting, if done abruptly, may cause nutritional deficiency. A prolonged period of fasting should always follow a proper intake of nutrition. When we fast, we focus most commonly on our calorie intake and ignore the nutritional requirements of our body. Thus for a successful fasting regimen, create a well-rounded nutritious diet plan. It is always better to consult a dietician and have a diet plan you can follow throughout your fasting period. Also, be careful of excessive calorie restriction as it may hamper the functioning of your body.


So is intermittent fasting for everyone?

The answer is it depends on person to person. For some people, it may work wonderfully. For others, it is not a good idea. Some people may experience side effects if they follow intermittent fasting. According to many doctors around the world, the following people should avoid intermittent fasting:

  • Pregnant and lactating mothers
  • Elderlies who experience weakness
  • Immunodeficient people
  • History of eating disorders like anorexia nervosa or bulimia nervosa
  • A person with dementia
  • History of traumatic brain injury
  • Children and teenagers who are in the growth phase


For people with a medical condition like diabetes or people on chronic medicines, it is always better to have a detailed discussion with the healthcare provider before starting the fasting regimen.


Some people may experience prolonged side effects during intermittent fasting. These side effects may signal that your body is not reciprocating well with these side effects.


Some of these side effects can be:

  • Extreme bouts of hunger
  • Continuous feeling of nausea
  • Tiredness and malaise
  • Headaches and lightheadedness


The conclusion:

Intermittent fasting has a long list of benefits attached to it. But it has its share of adverse effects as well. So if you feel miserable after your fasting regimen, stop doing it.

There are many other things apart from fasting which can give you sustainable health benefits. Also, you need to take care of your body during this fasting regimen. Get proper sleep, engage in physical activity, manage stress, and follow a balanced and nutritious diet plan. It is always better to check with your doctor before starting your fasting regimen.

Medanta Medical Team
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