There are trillions of microorganisms living in your intestines, helping to break down your food and make nutrients like B vitamins and vitamin K. Fasting can be one of the many ways to improve overall gut health by helping these microorganisms thrive.
Different types of fasting work for various people and lifestyles. Learn more about fasting and how it can help your gut.
When the organisms in your gut digest dietary fiber, they create compounds that researchers are finding critical to muscle function and disease prevention.
Your gut bacteria even affect your emotions and cognition. They help send signals between the brain and the digestive system—a connection known as the gut-brain axis.
Feeding your microbes the right stuff will balance the good and bad gut bacteria, giving you major health benefits. When the gut has a healthy balance of microbes, it reduces your chance of developing many types of chronic conditions, including:
- Asthma
- Chronic kidney disease
- Diabetes
- Heart disease
- Irritable bowel syndrome
- Mental health conditions
- Rheumatoid arthritis
To promote and support gut health, you can add more of the following to your diet:
- Apples
- Bananas
- Cheeses
- Garlic
- Kimchi
- Kombucha
- Miso paste
- Oats
- Onions
- Pickles
- Potatoes
- Rice
- Sauerkraut
- Sourdough bread
- Strawberries
- Tomatoes
- Yogurt
However, it's not just what you eat that impacts the delicate balance of microorganisms in your gut. Research has found that when you eat and don't, it affects your microbiome significantly.
Intermittent fasting (IF) is an eating pattern where you only eat during certain parts of the day. This type of fasting can be done in a variety of ways, but two examples are:
- Time-restricted feeding: Restrict your eating to a certain number of hours each day, fasting the rest of the time.
- Weekly IF: Restrict what you eat on two to three nonconsecutive days per week.
Research suggests that both methods may lead to weight loss and improved metabolic function, potentially lowering the risk of diabetes and cancer. However, many of the studies have been done on rodents, and the few studies done with humans have had mixed results, so much more research is needed to determine if these fasting approaches are effective.
Note: People who are pregnant or breastfeeding, and those who have a history of disordered eating, should not try any form of fasting.
IF works with your gut microbiome to help increase how efficient your metabolism is. IF can also change the makeup of your microbiome, making the bacteria more diverse.
There's a rapid expansion of a particular bacteria—Akkermansia muciniphila—that is associated with positive health markers, like decreased intestinal inflammation and a healthier gut barrier. Your gut barrier is the lining of the intestines. It lets nutrients pass through but blocks bacteria and other germs.
"Your gut bacteria are very responsive to the presence and absence of food," Suzanne Devkota, PhD, director of microbiome research at the F. Widjaja Foundation Inflammatory Bowel and Immunobiology Research Institute at Cedars-Sinai in Los Angeles, told Health. "When you remove food, the microbiome shifts in composition."
There are several IF patterns, but two common types are:
- 5:2 weekly fasting, where you eat normally for five days of the week and severely restrict food calories for two nonconsecutive days of the week
- 16:8 time-restricted feeding, where you fast for 16 hours and eat during the remaining eight hours
Fasting days don't have to be completely devoid of calories. Most plans recommend a 70% to 75% reduction in calories on fasting days, but even reducing 60% could make a difference, said Devkota.
Also, don't restrict your calorie intake during the eating periods. Instead, focus on portion control maintenance. Most of your gut bacteria need food to survive—not to mention you need food for energy and other functions—said Devkota.
Of note, there's no negative effect on gut diversity when you fast for a short time. However, when your body enters starvation mode—like if you fast for too long—you can decrease the diversity of bacteria in your gut. Gut diversity is why Devkota recommended making sure your fasting is "truly intermittent" and that you don't fast for two days in a row.
Eating by the Clock
A fasting regimen on a 24-hour cycle—like a 16:8 or 14:10 breakdown—allows you to align your fasting with your natural sleep/wake cycles. This is important because circadian rhythms regulate nutrient processing, Dorothy Sears, PhD, professor of medicine at the University of California San Diego School of Medicine, told Health.
For example, insulin is most effective in the morning and midday; insulin secretion decreases in the evening and overnight. "If you eat a snack at night, the insulin you secrete to process it isn't going to function as well as if you ate that same food for breakfast," said Sears.
By eating breakfast a touch later (say, 8 a.m. or 9 a.m.) and moving dinner a bit earlier (finishing around 6 p.m.), you can align your food intake with your circadian rhythm and still get that prolonged overnight fast without too much extra effort.
A healthy gut is associated with many health benefits and preventing chronic conditions. The different types of fasting can be one of many ways to improve gut health. Intermittent fasting can take several forms, including specific weekly day fasting and fasting based on the number of hours each day.
The fasting schedules can accommodate different preferences and schedules to achieve your best overall health. Before starting a fasting approach, discuss the best one for you with a healthcare provider.
