The Impact of Intermittent Fasting on Gut Health

Evidence suggests that intermittent fasting may benefit your gut health and boost your gut microbiome, the trillions of bacteria and other microorganisms that live in your gut.

Intermittent fasting is an approach to eating where you switch between periods of fasting and eating as normal. There are different types of intermittent fasting, and some may help to increase the diversity of your gut microbiome, as well as your levels of specific gut bacteria.

What you eat when you’re not fasting is also important when it comes to the health of your gut. There are some broad guidelines you can follow, but everyone responds to foods differently.

What is intermittent fasting?

Intermittent fasting is an eating plan that focuses on when you eat, rather than the specific foods you consume.

There are many different types of intermittent fasting, but with each method, you alternate between periods of eating and not eating — or fasting.

• Time-restricted eating: This involves fasting during certain hours of the day. It’s the most popular approach, as it extends the fast that happens naturally while you sleep.
• 5:2 fasting: With this method, you eat your normal diet for 5 days out of the week, then reduce the amount you eat on the other 2 days, usually to no more than 500–800 calories.
• Alternate-day fasting: This is similar to 5:2, but instead of fasting on 2 set days of the week, you alternate between days of eating as normal and days where you reduce your food intake.

Many people turn to intermittent fasting to improve their health. There are a number of possible benefits to the various methods, and recent evidence suggests intermittent fasting may also impact your gut health.

Can intermittent fasting help with gut health?

Research into how intermittent fasting impacts gut health is relatively new, but there’s evidence to suggest that it could help change the makeup of your gut microbiome, which is linked to your overall health.

Intermittent fasting may also improve the function of your gut barrier, the layers of cells that form the lining of your gut, which let nutrients pass through while protecting you from diseases and toxins.

One study involved healthy men observing fasting periods of around 16 hours per day — similar to the 16/8 method — during the Islamic holy month of Ramadan.

At the end of the month, the participants’ gut microbiomes had higher levels of Lachnospiraceae, beneficial bacteria that have been linked with a lower risk of cancer and inflammatory bowel disease, and improved heart health and mental health.

However, after they stopped daily fasting, the men’s gut microbiomes returned to their previous state.

In another study, a group of young men following the 16/8 approach saw a significant increase in their overall microbiome diversity. They also had higher levels of specific beneficial bacteria called Prevotellaceae and Bacteroidetes, which are associated with reduced markers for obesity and better metabolic health.

The natural fasting that happens as you sleep gives clues as to how extended fasting might also help with the health of your gut barrier.

During this time, activity in the gut slows down and the cells in your gut lining are repaired.

Scientists have suggested that lengthening this fasting time could help strengthen the gut barrier and, in turn, limit chronic inflammation, which can contribute to chronic health conditions like heart disease and type 2 diabetes.

Research is ongoing, but it could help explain some of the reported benefits of intermittent fasting.

What should you eat for gut health during intermittent fasting?

While there are no strict rules about what you can eat during non-fasting periods, if you’re looking to improve your gut health, certain foods may help.

Try fermented foods

Probiotics are bacteria similar to those found in your gut microbiome, and scientists believe they have health benefits.

You can get probiotics from fermented foods such as live yogurt, aged cheeses, kefir, kimchi, kombucha, and sauerkraut.

Once you’ve eaten these foods, the probiotic bugs may set up home in your gut, increasing the diversity of beneficial bacteria and the health of your gut microbiome.

Eat more plants

Eating plenty of plants is also important for your gut health. Many plant foods, such as onions, leeks, asparagus, garlic, and whole grains contain prebiotics, a type of fiber that feeds the “good” bacteria in your gut and helps them to thrive.

Regularly eating plants rich in fiber and high-quality protein — for example, lentils, beans, nuts, and quinoa — can also help you feel fuller for longer.

Eat fewer processed foods

Eating lots of ultra-processed foods, with added sugar, fat, salt, and artificial ingredients, is linked to health conditions like heart disease and type 2 diabetes. And it’s not good for your gut microbiome, either.

Ultra-processed foods like sugary sodas, candy, cookies, breakfast cereals, hot dogs, and pre-made pizzas don’t provide your gut bugs with the fiber and other nutrients they need.

Our research also shows that they are linked to “bad” gut microbes that are associated with worse health outcomes.

Eat for your unique gut microbiome

Our research shows that how your body and your gut microbes respond to the foods you eat is unique to you.

Summary

Intermittent fasting is an eating pattern that involves periods of the day where you don’t eat — or days where you significantly reduce your food intake — alternating with periods where you eat as normal.

Initial evidence suggests that intermittent fasting may benefit your gut health, particularly by increasing the diversity of your gut microbiome and the “good” gut bugs that make their home there.

Certain foods may improve your gut health while intermittent fasting, as well as help support you during fasting periods. These include fermented foods containing probiotics, as well as plant foods and whole grains — especially those with prebiotics that provide fuel for your gut bugs.

FAQs

How many hours of fasting to heal a gut?

There is no single, defined fasting duration to fully “heal” the gut. The gut can become damaged for many reasons, and fasting may not deal with all of them.

Is fasting bad for high cortisol?

If you have a preexisting health condition, speak to your doctor before changing your eating patterns.

Is intermittent fasting safe?

When done correctly, intermittent fasting is safe for most people. However, people who are pregnant or breastfeeding, people with type 1 diabetes, and anyone with a history of disordered eating shouldn’t try intermittent fasting.

Older adults and people who need to take medication with food should speak with a doctor before trying any type of fast.