Why does intermittent fasting cause diarrhea?

Why does intermittent fasting cause diarrhea?


Intermittent fasting has gained popularity as a weight loss and health improvement strategy. However, some individuals may experience an unpleasant side effect – diarrhea. This article will explore the potential reasons why intermittent fasting can cause diarrhea and provide insights into managing this issue.

Potential Causes of Diarrhea during Intermittent Fasting

Changes in Gut Microbiota

Intermittent fasting can alter the composition of gut microbiota, which refers to the trillions of microorganisms residing in our digestive system. When we fast, the reduction in food intake and changes in eating patterns can affect the diversity and balance of gut bacteria. This disruption may lead to digestive issues, including diarrhea. It is important to note that the impact on gut microbiota can vary among individuals, and more research is needed to fully understand this relationship.

Increased Fiber Intake

Intermittent fasting often involves consuming larger meals in a shorter eating window. This can lead to an increased intake of dietary fiber, especially if individuals choose to include more fruits, vegetables, and whole grains in their meals. While fiber is generally beneficial for digestion, a sudden increase in fiber intake can cause diarrhea, especially if the body is not accustomed to processing large amounts of fiber. Gradually increasing fiber intake and ensuring adequate hydration can help prevent this issue.

Changes in Hormones

Intermittent fasting affects various hormones in the body, including insulin, ghrelin, and glucagon. These hormonal changes can influence digestion and bowel movements. For example, fasting may increase the release of bile acids, which can speed up intestinal transit and potentially lead to diarrhea. Additionally, fasting-induced changes in hormone levels can affect water absorption in the colon, leading to looser stools. However, it is important to note that the impact of hormonal changes on bowel movements may vary among individuals.


Dehydration can be a contributing factor to diarrhea during intermittent fasting. When fasting, individuals may not consume enough fluids, leading to dehydration. Inadequate hydration can soften stools and cause diarrhea. It is crucial to stay well-hydrated during fasting periods by drinking water and other non-caloric beverages.

Managing Diarrhea during Intermittent Fasting

Gradual Adjustment

If you experience diarrhea when starting intermittent fasting, it may be helpful to gradually adjust your fasting schedule. Start with shorter fasting periods and gradually increase the duration as your body adapts. This approach allows your digestive system to adjust to the changes more smoothly, potentially reducing the occurrence of diarrhea.

Monitor Fiber Intake

Monitor your fiber intake and ensure it is well-balanced. Gradually increase fiber-rich foods in your diet to allow your body to adjust. If you notice that certain high-fiber foods trigger diarrhea, consider reducing their consumption or opting for alternative sources of fiber.

Stay Hydrated

Maintaining adequate hydration is essential during intermittent fasting. Drink plenty of water throughout the day, even during fasting periods. Avoid excessive consumption of caffeinated beverages or sugary drinks, as they can contribute to dehydration. Electrolyte-rich beverages, such as coconut water or sports drinks, can also help replenish lost fluids.

Consider Supplements

In some cases, supplements may be beneficial in managing diarrhea during intermittent fasting. Probiotics, for example, can help restore the balance of gut bacteria and improve digestive health. However, it is important to consult with a healthcare professional before starting any new supplements.


While intermittent fasting offers numerous health benefits, it can sometimes lead to diarrhea. The potential causes include changes in gut microbiota, increased fiber intake, hormonal changes, and dehydration. By gradually adjusting fasting schedules, monitoring fiber intake, staying hydrated, and considering supplements, individuals can manage and minimize the occurrence of diarrhea during intermittent fasting.


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