Why Does Intermittent Fasting Cause Diarrhoea

Intermittent fasting (IF) is a popular diet trend that involves restricting food intake for specific periods. While it has been known to promote weight loss, some people experience diarrhoea during fasting. Diarrhoea can be uncomfortable and embarrassing, but it is also an indication that something is amiss with your digestive system. However, the real question is, why does intermittent fasting cause diarrhoea?

Intermittent fasting may cause diarrhoea due to abrupt dietary changes, which can disrupt gut microbiota balance. During fasting periods, the digestive system slows down, and when food is reintroduced, it can trigger bowel movements. Additionally, consuming large meals or high-fibre foods in a short time frame may exacerbate diarrhoea.

This blog post will address the link between intermittent fasting and diarrhoea. We will also delve into scientific explanations for this phenomenon, factors that increase the risk of diarrhoea during IF, and tips to help you avoid or manage diarrhoea. Lastly, we will discuss when to seek medical help if you experience persistent diarrhoea during intermittent fasting. So, let’s get started on unlocking the mysteries behind this common issue so that you can continue reaping the benefits of IF without any discomfort.

The Link Between Intermittent Fasting and Diarrhea

Starting an intermittent fasting routine can have various health benefits, such as weight loss and improved insulin sensitivity. However, some individuals experience digestive discomfort, such as diarrhoea. Several factors, including changes in the gut microbiome and dehydration, can cause diarrhoea during intermittent fasting. Understanding the link between intermittent fasting and diarrhoea is crucial so that you can take the necessary precautions to prevent it. In this section, we will explore scientifically-backed explanations for diarrhoea during intermittent fasting and factors that increase the risk of it. (1)

Scientific Explanations for Diarrhea During Intermittent Fasting

The scientific explanations for diarrhoea during intermittent fasting can be attributed to multiple factors. One of the primary reasons is changes in the gut microbiome due to prolonged periods of fasting, which can lead to an imbalance in gut bacteria and trigger diarrhoea. Rapid changes in diet and eating patterns during intermittent fasting can also cause digestive issues, including diarrhoea. Additionally, dehydration and electrolyte imbalances caused by fasting may further contribute to diarrhoea. Certain medications or supplements taken during intermittent fasting may also lead to diarrhoea as a side effect. (2)

#1 Changes in Gut Microbiome

The gut microbiome is a complex community of microorganisms that are essential for healthy digestion and overall well-being. Intermittent fasting can disrupt this delicate balance, leading to diarrhoea and other digestive issues. Fasting can cause an overgrowth of harmful bacteria, leading to inflammation and diarrhoea. It’s crucial to maintain hydration levels during fasting periods and gradually reintroduce food back into your diet to minimize these effects. Incorporating high-fibre foods during eating periods can also help regulate bowel movements and support a healthy gut microbiome. (3)

#2 Changes in Gastric Emptying and Secretion

Fasting can significantly impact gastric emptying and secretion, leading to changes in digestion that may trigger diarrhoea. Gastric emptying refers to the rate at which food moves out of the stomach and into the small intestine. The stomach may become less active during fasting, leading to slower gastric emptying. As a result, food can remain in the stomach for longer periods, leading to diarrhoea when it eventually exits into the intestines. Additionally, changes in gastric secretion, such as increased bile production, can contribute to diarrhoea during intermittent fasting. (4)

#3 Low-Fiber Diet during Fasting

Maintaining a healthy diet during intermittent fasting is crucial to avoid digestive issues like diarrhoea. However, some people may not incorporate enough fibre into their diets during the fast, which can lead to changes in bowel movements. Fibre plays a vital role in maintaining regularity and promoting healthy digestion. Therefore, it’s essential to include high-fibre foods during non-fasting periods to prevent diarrhoea and other digestive problems.

diarrhea diet

Factors that Increase the Risk of Diarrhea During Intermittent Fasting

Maintaining a healthy digestive system is a crucial aspect of overall well-being, and the risk of digestive disturbances increases with rapid changes in diet. During intermittent fasting, dehydration can occur, leading to diarrhoea. Consuming high-fibre foods during the eating window can also increase the chances of diarrhoea. Existing digestive conditions such as irritable bowel syndrome (IBS) can be aggravated by intermittent fasting, and it may disrupt the delicate balance of gut bacteria. Adhering to healthful practices like gradual increases in fasting duration, low-fat food choices when breaking fasts, hydration, and probiotic consumption can help mitigate these risks.

Tips to Avoid or Manage Diarrhea During Intermittent Fasting

Integrating intermittent fasting into your lifestyle can be challenging, but it doesn’t have to be a painful experience. Here are some tips to help you avoid or manage diarrhoea during intermittent fasting.

#1 Hydrate, Hydrate, Hydrate!

Staying hydrated is crucial when it comes to avoiding diarrhoea during intermittent fasting. Drinking plenty of water and electrolyte-rich fluids can help keep the digestive system functioning smoothly and prevent dehydration-related diarrhoea. Additionally, gradually easing into intermittent fasting can help reduce the risk of diarrhoea by giving your body time to adjust to the new eating patterns. In some cases, taking probiotics or digestive enzymes may also be helpful in maintaining healthy bowel movements while fasting.

#2 Start Slow and Gradually Increase Fasting Duration

Gradually increasing the duration of your fasting period is one way to reduce the risk of diarrhoea during intermittent fasting. Starting slow and allowing your body time to adjust to the changes in diet is important. Jumping straight into longer fasting periods can shock your digestive system and lead to diarrhoea. It’s essential to listen to your body and take breaks from fasting if necessary.

fasting duration

#3 Break the Fast with Light, Low-Fat Foods

Breaking the fast with light, low-fat foods is crucial in managing diarrhoea during intermittent fasting. High-fiber and high-fat foods can trigger digestive issues when breaking a fast, so it’s best to stick to easily digestible options like fruits, vegetables and lean proteins such as chicken or fish.

#4 Incorporate Probiotics and Prebiotics in Your Diet

Maintaining a healthy gut microbiome can be crucial in managing diarrhoea during intermittent fasting. One way to promote a healthy gut is by incorporating probiotics and prebiotics into your diet. Probiotics are live bacteria that help maintain a healthy gut microbiome and aid in digestion, while prebiotics are non-digestible fibres that promote the growth of beneficial bacteria in the gut. Foods like yoghurt, kefir, sauerkraut, and bananas are rich sources of both probiotics and prebiotics.

#5 Avoid Carbonated Drinks and Artificial Sweeteners

When it comes to avoiding or managing diarrhoea during intermittent fasting, paying attention to what you’re drinking is essential. Carbonated drinks and artificial sweeteners can aggravate the digestive system and lead to diarrhoea, so avoiding them altogether is best. Instead, opt for plain water or herbal tea to stay hydrated. If you need a little flavour, try adding a slice of citrus or cucumber to your water.

When to Seek Medical Help for Diarrhea During Intermittent Fasting

When it comes to diarrhoea during intermittent fasting, seeking medical help may be necessary if symptoms persist for more than a few days. While changes in gut bacteria and increased bile production may contribute to the issue, persistent diarrhoea could indicate an underlying condition requiring a healthcare professional’s attention. Staying hydrated during this time is important, as dehydration can be a potential risk when experiencing diarrhoea during intermittent fasting. Adjusting the timing and duration of fasting periods and gradually introducing new foods may help alleviate symptoms.

When to Seek Medical Help for Diarrhea During Intermittent Fasting (1)

How Long Does Diarrhoea Last During Intermittent Fasting?

Diarrhoea during intermittent fasting typically lasts for a few days to several weeks. This is because the body takes time to adjust to the changes in dietary habits and increased water intake that come with intermittent fasting. In most cases, diarrhoea during intermittent fasting is mild and resolves on its own within a few days. However, if diarrhoea persists for more than a week or is accompanied by other symptoms such as fever or abdominal pain, it’s essential to seek medical help.

Can Intermittent Fasting Cause Other Digestive Issues Apart From Diarrhoea?

Intermittent fasting can lead to various digestive issues apart from diarrhoea, such as constipation and bloating. These problems arise due to changes in the gut microbiome and meal timing. Staying hydrated and consuming fibre-rich foods during eating periods is essential to prevent these issues. In some cases, persistent digestive problems may require medical attention, and a healthcare provider may recommend dietary changes or medications to alleviate the symptoms. Maintaining a balanced diet and monitoring any unusual symptoms during intermittent fasting is vital.


Intermittent fasting can lead to diarrhoea due to changes in the gut microbiome, gastric emptying and secretion, and a low-fibre diet during fasting. However, there are ways to avoid or manage diarrhoea during intermittent fasting, such as hydrating well, starting slow and gradually increasing fasting duration, breaking the fast with a light, low-fat foods, and incorporating probiotics and probiotics and probiotics prebiotics in your diet while avoiding carbonated drinks and artificial sweeteners. If you experience persistent or severe diarrhoea during intermittent fasting or have underlying digestive disorders, it is important to seek medical help.

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