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Does Fasting Kill Gut Bacteria? (It’s That Easy??)

Fasting is a method of trying to lose weight or improve your health by stopping eating completely, or almost completely, for a certain amount of time. 

Fasting usually lasts anywhere between 12 to 24 hours, depending on the method.

Some people start fasting in order to lose weight, but others do so because they believe it can improve their digestive health.

In fact, some studies show that fasting can actually kill gut bacteria and improve the health of your digestive system. But is there any truth to it?

Does Fasting Kill Gut Bacteria?

Prolonged periods of fasting actually do kill gut bacteria, improving overall gut microbiome diversity. Fasting also appears to improve gut health and improve the health of the ‘good’ gut bacteria in your digestive tract.

Aside from that, fasting can help you achieve a calorie deficit much easier, contributing to healthy and steady weight loss. Thanks to that, you can shed some pounds without trying too much.

So, if you’re looking for a way to improve your gut health while losing weight, fasting might be the way to go.

How does fasting kill gut bacteria?

Fasting can help reset your gut and improve the health of your digestive system. It allows you to clean your digestive system, flushing out all toxins and harmful chemicals accumulated from all the foods you have consumed.

In order to fast to clean out your gut, make sure to fast for at least 16 hours every three days or so. That way, you can start cleaning out your gut and healing your digestive system.

The way fasting heals your gut is that it allows it to rest without being forced to digest any food. 

This gives your digestive system time to relax, not produce gastric acid, and focus on repair rather than digestion.

So, even if you don’t have an unhealthy gut, it might be beneficial for you to try intermittent fasting from time to time.

Some of the foods you have to consume on a diet aimed at killing harmful gut bacteria are probiotics and prebiotics.

These two food types are required for the proper functioning of your digestive system. Without them, you can’t fast properly, and you risk serious damage to your digestive tract.

Probiotics include milk, yogurt, sauerkraut, fermented pickles, kombucha, and similar. These help add to the healthy gut bacteria already present in your gut.

Prebiotics are food for the gut bacteria, which means that they help them stay alive and keep you healthy. 

These foods include many high-fiber foods like avocados, asparagus, spinach, whole grains, fruits, and similar.

So, make sure to include these in the meals you’re eating in the hours you’re not fasting. If you don’t, you might not get the same benefits from your fast as you would otherwise.

Does fasting kill good or bad gut bacteria?

Healthy fasting – which means without overdoing it – can help you clean out your gut without damaging and harming the healthy gut bacteria in your digestive tract.

When fasting, make sure to drink water, though. Fasting is about not eating for certain periods of time, but drinking water is important.

Proper hydration is important for healthy metabolism, immune system, and gut health. 

Studies show that fasting with drinking plenty of fluids helps improve gut bacteria diversity and protect your digestive tract. Without fluids, you can develop serious health complications.

If you find it hard to drink plain water, you can drink lemon-infused water. But make sure not to add too much, as too many calories can break your fast. 

But it’s still important to drink enough water during your fast, so adjust your beverages as you wish.

Why should you use fasting to kill gut bacteria?

Fasting can help you bring balance back to your digestive system. It helps you improve your digestion, prevent diarrhea and constipation, and reduce the frequency of nausea.

Aside from digestive system benefits, killing harmful gut bacteria can also help you in other ways. Some of the other benefits include:

  • Faster metabolism
  • More energy
  • Better sleep
  • Clearer skin
  • Speedier weight loss

In the longer run, fasting can help you improve your cognitive function, producing healthy neurotransmitters.

So, you can get a lot more than just a better digestive system from fasting. Fasting also has another great benefit, which is that it helps you stay hydrated.

Sometimes, people forget about drinking enough water throughout the day. But when you fast for hours, you have to drink enough fluids not only to keep your energy levels up but also to prevent any false feelings of hunger.

Oftentimes, people confuse thirst for hunger. So, drinking enough water can help you fast and avoid eating before your fasting period ends. 

Can fasting and killing gut bacteria help you fight infections?

A recent study shows that fasting can help your body fight against several infections in your digestive system.

This is because it kills harmful gut bacteria that can often cause inflammation and irritation in your digestive tract. 

The harmful gut bacteria are often responsible for digestive problems like constipation, stomach flu, indigestion, and many more. So, by getting rid of these bacteria, you can prevent these issues from developing.

In addition, fasting can also help prevent bacterial infections caused by food and environmental factors. 

Because of that, fasting can be beneficial to those prone to bacterial infections of the digestive system.

How long should you fast for a healthy gut?

Fasting for a healthy gut should last about 16 hours every three days. During the fasting period, make sure to drink plenty of fluids to avoid dehydration and keep your metabolism working.

Studies show that this whole process should last about 30 days minimum in order to starve the harmful gut bacteria and improve the health of your digestive system.

Overall, most people will need about six months to fully cleanse their gut and notice some real benefits. 

So, it all depends on the condition of your digestive system before starting your fasting journey.

Aside from fasting, make sure to follow an otherwise healthy diet in the hours that you’re allowed to eat. This means that you should consume fresh produce with each meal and avoid processed junk food.

The foods that you can consume include:

  • Whole grains
  • Lean meat and fish
  • Low-fat dairy
  • Plenty of fresh fruits, such as apples or oranges
  • Lots of vegetables, such as broccoli or kale

These foods help feed the ‘good’ gut bacteria in your stomach, stopping any damage to them that might happen as a result of fasting.

Can you eliminate all ‘bad’ bacteria through fasting?

Unfortunately, you’re very unlikely to kill all the harmful gut bacteria in your digestive tract. 

Fasting can help you decrease the number of bad bacteria and toxins, but only a healthy diet can fully heal your gut.

With that being said, remember that simply eating one healthy meal every once in a while won’t heal your gut. 

The key is consistency. Consuming unhealthy foods sometimes won’t harm your gut as long as you follow a healthy diet aside from that.

Some research also indicates that it might be nearly impossible to get rid of all harmful gut bacteria in your digestive tract. 

Luckily, though, if you follow a healthy, balanced diet, the remaining ‘bad’ bacteria shouldn’t cause you too much trouble.

This is because they usually stay dormant when you consume healthy food, as you’re primarily feeding the ‘good’ gut bacteria that help offset the negative effects of the other type of bacteria.

Can fasting damage your gut?

When fasting, it’s important to stick to a specific period of time and not go too long without eating. If you overdo it, you can develop serious digestive system problems.

If you stop eating for too long, you can cause all the bacteria in your stomach to eat the mucus in the lining of your gut. 

This destroys the membrane protecting your digestive tract and can cause the dangerous bacteria to infect the colon wall and even get into your blood.

So, while fasting can be good for getting rid of harmful gut bacteria, fasting for too long can bring the opposite effect.

Plus, when fasting, make sure to consume fiber-rich foods. These are prebiotics that feed the ‘good’ gut bacteria. 

This is important as these bacteria keep your gut healthy, so if they’re starved, you can bring yourself more harm than good.


Fasting can be a great way to clean out your gut and kill harmful gut bacteria that reside in your digestive tract. Thanks to that, you can improve your digestive health, especially if you’ve gone through digestive system problems, such as stomach flu.

What’s more, fasting can help you lose weight in a healthy, steady way. This can be beneficial if you’re struggling to limit your intake of calories throughout the day.

So, if any of the above apply to you, you might want to give fasting a shot.

Sources: National Library of Medicine, PMC, Science Direct, and PLOS