Top 5 Intermittent Fasting Side Effects Resolved

Dieser Artikel basiert auf wissenschaftlichen Studien

Intermittent Fasting | Side Effects | Fatigue | Headache | Diarrhea | Hunger

Beginners’ mistakes cause side effects during intermittent fasting that may negate health benefits. Here, you can find out what you have to pay attention to avoid or resolve the side effects of fasting.

How Does Intermittent Fasting Work?

Intermittent fasting 16/8 has experienced a real boom in recent years. One of the primary triggers for this was probably the award of the Nobel Prize for the health benefits of fasting.

The Japanese Yoshinori Ohsumi was awarded the Nobel Prize for Medicine in 2016 for his discovery of autophagy, which means self-healing.

Fasting induces this natural cleansing mechanism, which replaces broken cell components with new ones and drains toxins from the body (Levine et al. 20171).

Accordingly, intermittent fasting benefits the body and the immune system.

Therefore, the following health benefits of intermittent fasting do not claim to be complete:

  • weight loss
  • higher energy level
  • reduced risk of cardiovascular diseases
  • reduced risk of diabetes
  • improved insulin sensitivity
  • lower blood sugar
  • improved blood pressure
  • improved digestion and gut health
  • whole body detox
  • less inflammation

Also, many fasting advocates have noticed improved blood sugar and fat levels long-term.

Intermittent Fasting Side Effects and How to Resolve Them

When you start fasting, unconscious beginner’s mistakes happen. The absence of weight loss is usually depressing and demotivating.

By following these tips, you can get the health benefits of intermittent fasting from day one without the risk of developing eating disorders.

#1: Fatigue

A big myth about fasting is that you have to take it easy. On the contrary, you should be active, especially when feeling tired.

Rest is the safest way to feel terrible if you feel tired during fasting. Instead, activities help the body burn fat more efficiently as its primary energy source.

Since our body tries to save energy, fat-burning requires physical activity.

If you feel tired, it is often a symptom that the carbohydrate stores are depleting. However, we can only burn fat efficiently when these short-term energy stores are empty.

Then the body signals sluggishness or hunger that quickly available energy is running low. And it doesn’t want to spend additional metabolic energy on burning body fat.

Accordingly, body fat acts like a savings account tackled when the checking account – the carbohydrate stores – is empty (Fung 20162).

Hence, it helps to increase energy use through exercise slightly. This way, you force your body to switch to burning body fat for energy.

Intermittent Fasting 16/8 for Women Book

Another mistake when fasting would be to exaggerate immediately with an intensive workout. On the other hand, a regenerative walk or yoga can help to get fat-burning going.

Nevertheless, it is crucial to listen to your body when fasting. If you feel great with fasting and intensive resistance training, do so.

However, you can break a fast any time when feeling unwell.

For me, strength training and intermittent fasting work very well. Since fasting releases increased growth hormones, the right balance of intermittent fasting and strength training promotes muscle gain.

The situation is different with endurance training, such as marathon preparation. In my experience, the body’s increased appetite and need for recovery are counterintuitive.

But if you feel tired, grab a bike or walk the dog.

How to Be More Active:
  • Be active: If you feel light-headed, don’t stop moving altogether. Otherwise, you will become even more tired.
  • Keep routines: Treat the fasting day or period like any other. Although fasting beginners are usually nervous, it is no big deal. Nature has designed our bodies for it. Therefore, especially when you are worried, avoid standing still and distract yourself with house or garden work.
  • Exercise mildly: If you feel tired, a 15-minute walk usually helps.

#2: Headaches

Apart from fat, hardly anything has been so dismantled for decades as salt. Not only advertising campaigns but also doctors have partly caused this. Yet salt is not as bad as its image.

Few people are aware that we cannot survive without salt. Although a daily maximum of two grams is often recommended, our ancestors instinctively absorbed 2-3 times as much salt.

Surprisingly, even today, countries with the highest salt consumption have the lowest rates of cardiovascular disease (Park et al. 20163).

Additionally, salt is the natural antagonist of sugar, removes the bitter taste from our food, and counteracts cravings.

In contrast to sugar, salt also has a positive feedback loop. When your body has had enough salt, you no longer feel like it.

For example, I have problems eating oversalted soup – what about you?

With cake, however, things look different.

Moreover, research suggests that insufficient salt intake is more harmful to our health than vice versa.

Accordingly, the endocrinologist and fasting pioneer Dr. Jason Fung reports that most physical intermittent fasting side effects are due to lack of salt. These include headaches and fatigue (Fung 20164).

Furthermore, he observed in his diabetes practice that salt intake is essential for losing weight, especially in women. Hence, salt helps to prevent type 2 diabetes.

While sugar consumption promotes insulin resistance and storage of body fat, salt increases insulin sensitivity and helps lose weight (Sakuyama et al. 20165).

pink Himalayan salt on a wooden plate

Celtic Sea Salt or Pink Himalayan Salt are good options to bring healthy salt into your diet. Since these salts usually don’t contain additives such as anti-caking agents, they are more natural.

It’s advisable to consult your doctor before changing your diet. People with chronic kidney disease or certain cardiovascular diseases must pay attention to their sodium intake.

How to Get More Salt Into Your Diet:
  • Salt to taste: Listen to your body and dare to salt food properly when it asks for it.
  • Eat bone broth: Many fasting beginners find it helpful to drink bone broth or sugar-free juice from pickles until the body gets used to the lifestyle.
  • Drink saltwater: If you have neither sugar-free pickle juice nor bone broth at hand, dissolve a pinch of salt in a glass of water, a cup of tea, or coffee, especially when starting with intermittent fasting.
  • Cut carbs: Processed carbohydrates bind water in the body. So if you eat refined carbohydrates between fasting periods, you will lose a lot of water afterward. Therefore, large amounts of sodium leave the body, which causes headaches.

#3: Diarrhea

Excess water and salts will be flushed out through the gastrointestinal tract if you start intermittent fasting.

There can be different triggers, such as too much caffeine. Nevertheless, intermittent fasting alone does not cause diarrhea or constipation. Food does. For example, too much fiber can cause constipation.

You are more likely to get diarrhea if you break the fast. But that’s just natural when the gastrointestinal tract starts working again.

Moreover, diarrhea during fasting can be due to poor diet choices during eating periods:

  • Refined carbohydrates
  • Milk products (lactose or also milk proteins)
  • Legumes that are rich in fiber

These foods can cause irritability in your gut.

How to Avoid Diarrhea Through Diet:
  • Water: Increased water consumption is necessary against dehydration
  • Bone broth: Electrolyte supply through bone broth, cucumber water, or saltwater also helps with diarrhea.
  • Other drinks: Avoid sweetened beverages, caffeinated drinks, and diet soda.

#4: Cravings

A common mistake in intermittent fasting is that thirst is confused with hunger.

Instead of reaching for water or tea, we reach for a granola bar. Because food also provides us with liquid. However, we usually do not replace this liquid with water if we give up our usual snacks.

As a result, we feel hungry. Accordingly, you often have liquid food cravings during fasting and between meals.

Accordingly, some people need to be reminded regularly in their everyday life to drink enough fluids.

So, how much should you drink during Intermittent fasting?

Fluid intake during intermittent t fasting cannot be generalized. No 5 liters per day are recommended for every person, nor can the water requirement be calculated based on weight, height, and age.

Especially since overhydrating is just as harmful as dehydration, there is a simple rule of thumb: drink when thirsty.

You do not have to force yourself to drink if you are not thirsty. The same should apply to everyday life.

In case of doubt, a glass of water or tea won’t hurt. After experiencing extended fasting periods, you will get a better feeling about whether you are thirsty.

How to Get Hydrated:
  • Carbonated water: Mineral water is particularly suitable for relieving hunger. Additionally, it supplies the electrolytes that we flush out with our urine.
  • Fluid Intake: If you feel hungry, drink tea or water and wait 30 minutes. When hunger subsides, you are only thirsty.
  • Alarm clock: If you have difficulty absorbing enough fluids, use your mobile phone’s alarm clock as a reminder.

#5: No Results

Most people drink water, black coffee, or tea during fasting. However, mistakes are often made during intermittent fasting.

Therefore, fasting beginners often add milk or sugar to their coffee, not expecting a real impact.

But such little things will break the fast by increasing blood sugar and insulin levels. The impact on insulin levels is more critical to intermittent fasting than counting calories.

Accordingly, keto dieters repeatedly forget that Bulletproof Coffee breaks a fast.

While butter, coconut, or MCT oil in the coffee helps against hunger, it prevents the health and weight loss effects of fasting.

Although bone broth is an excellent source of electrolytes and fat, it should only be used as a jump-start due to the insulin reaction. Once you adapt to intermittent fasting, there is no reason to consume it frequently.

Moreover, many people do not know diet soda does not trigger blood sugar but can spike insulin.

For example, it prevents autophagy. Also, sweeteners stimulate cravings in the brain’s reward center.

How to Not Break Your Fast:
  • A squirt of lemon or lime
  • Orange or cucumber slices
  • Diluted apple cider vinegar
  • A pinch of salt

The Bottom Line

Although unconscious mistakes during intermittent fasting can cause side effects, and your body needs time to get used to the lifestyle, the benefits of fasting outweigh the disadvantages.

In essence, intermittent fasting saves time and money, improves metabolism, and helps to reverse insulin resistance and even type 2 diabetes (Furmli et al. 20186).

However, fasting means that you cannot drink juices or smoothies. Anything that triggers an insulin reaction, such as diet soda, almond milk, or coconut oil, breaks the fast.

Since you know common intermittent fasting mistakes and their side effects, there’s no reason to fear fasting. It’s way simpler than any diet out there.

intermittent fasting for beginners book

Frequently Asked Questiosn (FAQ)

What are the negative effects of intermittent fasting?

Due to beginner’s mistakes, intermittent fasting can cause side effects such as headaches, cravings, diarrhea, constipation, or fatigue.

What happens to your body when you fast for 16 hours?

The storage hormone insulin drops with the duration of fasting and allows your body to tap into body fat for energy more efficiently.

What are 3 disadvantages of intermittent fasting?

If not done correctly, intermittent fasting can cause common side effects such as headaches, cravings, or fatigue.

What are the positive side effects of intermittent fasting?

The positive side effects of intermittent fasting comprise weight loss, insulin sensitivity, cancer, Alzheimer’s, Parkinson’s, and heart disease prevention.


1Levine B, Klionsky DJ. Autophagy wins the 2016 Nobel Prize in Physiology or Medicine: Breakthroughs in baker’s yeast fuel advances in biomedical research. Proc Natl Acad Sci U S A. 2017 Jan 10;114(2):201-205. doi: 10.1073/pnas.1619876114. Epub 2016 Dec 30. PubMed PMID: 28039434; PubMed Central PMCID: PMC5240711.

2Fung J. The Obesity Code: Unlocking the Secrets of Weight Loss. Vancouver: Greystone Books, 2016.

3Park J, Kwock CK, Yang YJ. The Effect of the Sodium to Potassium Ratio on Hypertension Prevalence: A Propensity Score Matching Approach. Nutrients. 2016 Aug 6;8(8). doi: 10.3390/nu8080482. PubMed PMID: 27509520; PubMed Central PMCID: PMC4997395.

4Fung J. The Obesity Code: Unlocking the Secrets of Weight Loss. Vancouver: Greystone Books, 2016.

5Sakuyama H, Katoh M, Wakabayashi H, Zulli A, Kruzliak P, Uehara Y. Influence of gestational salt restriction in fetal growth and in development of diseases in adulthood. J Biomed Sci. 2016 Jan 20;23:12. doi: 10.1186/s12929-016-0233-8. Review. PubMed PMID: 26787358; PubMed Central PMCID: PMC4719732.

6Furmli S, Elmasry R, Ramos M, Fung J. Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin. BMJ Case Rep. 2018 Oct 9;2018. doi: 10.1136/bcr-2017-221854. PubMed PMID: 30301822; PubMed Central PMCID: PMC6194375.

Mag. Stephan Lederer, MSc.

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

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