5 Common Mistakes Cause Intermittent Fasting Side Effects

Dieser Artikel basiert auf wissenschaftlichen Studien

Common mistakes cause intermittent fasting side effects that negate the health benefits of fasting. Here you can find out what you have to pay attention to.

Health Benefits of Intermittent Fasting

Intermittent fasting 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, the effect of intermittent fasting brings numerous benefits for the body and the immune system.

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

  • weight loss
  • reduced risk of cardiovascular diseases
  • reduced risk of diabetes
  • improved insulin sensitivity
  • improved gut health
  • whole body detox
  • less inflammation

Also, many advocates of fasting have noticed improved blood sugar and blood fat levels. However, unintentional mistakes often happen when fasting.

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Common Mistakes Causing Intermittent Fasting Side Effects

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 interval fasting from day one:

1. Side Effect: Feeling Tired – Too Little Activity

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

If you feel tired during a fasting period, the safest way to feel terrible is to rest. Instead, activities help the body to burn fat more efficiently as its primary source of energy.

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

If you feel tired, it is often a sign 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 with 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 that 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.

Another mistake made 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 an increased amount of 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.

What you can do about feeling tired during fasting:

  • 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 body 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. Side Effect: Headache – Too Little Salt

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 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 the other way around.

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).

Too little salt is common intermittent fasting mistake causing side effects

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

Nevertheless, it is advisable to consult your doctor before changing your diet.

After all, people with chronic kidney disease or certain cardiovascular diseases must pay attention to their sodium intake.

How to avoid physical side effects such as headaches when fasting:

  • 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. Side Effect: Diarrhea – Poor Diet

If you start intermittent fasting, excess water and salts will be flushed out through the gastrointestinal tract.

There can be different triggers, such as too much caffeine. Nevertheless, intermittent fasting alone does not cause diarrhea.

In fact, 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 the mistakes in your diet between fasting periods:

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

What you can do about diarrhea while fasting:

  • 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. Side Effect: Hunger – Too Little Water

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, during fasting periods and between meals, you often do not have food cravings, but liquid.

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. Neither do recommendations of 5 liters per day apply to every person, nor can the water requirement be calculated based on weight, height, and age.

Especially since overwatering is just as harmful as dehydration. Nevertheless, there is a simple rule of thumb: Drink when you are thirsty.

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

In case of doubt, a glass of water or tea won’t hurt. During more extended periods of fasting and with experience, you will get a better feeling for whether you are thirsty.

What you can do about hunger during the fast:

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

5. Side Effect: No Results – Milk in Your Coffee

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

Therefore, fasting beginners often add a dash of 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 loss of health benefits is the side effect.

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

While butter, coconut, or MCT oil in the coffee helps against hunger in between, 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 adapted to the intermittent fasting lifestyle, 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.

What you can add to beverages instead of milk during intermittent fasting:

  • A squirt of lemon or lime
  • Orange or cucumber slices
  • Diluted apple cider vinegar
  • A pinch of salt

Don’t Fear Intermittent Fasting Side Effects

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, milk, almond milk, or coconut oil, breaks the fast.

Since you are now aware of common intermittent fasting mistakes and their side effects, there’s no reason to be afraid of fasting. It’s way simpler than any diet out there.

Intmittent Fasting Side Effects FAQ

How long should you do intermittent fasting?

How long you stick to intermittent fasting is entirely up to you. Some people see great results with sticking to 16/8 intermittent fasting. Others fast for 36 hours straight once a week and like that. You can even mix things up to surprise your metabolism and lose weight.

Can intermittent fasting make you sick?

Due to some beginner’s mistakes, intermittent fasting can cause side effects such as headaches or fatigue when not done correctly.

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.

Can intermittent fasting cause problems?

If not done correctly, intermittent fasting can cause common side effects such as headaches or fatigue. Being active and consuming salt 🧂 can help.


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.

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