What Is Intermittent Fasting?
Intermittent fasting has become an increasingly popular diet and lifestyle approach. It involves cycling between periods of fasting and eating. Rather than restrict what foods you eat, it dictates when you eat them. It may promote weight loss and provide other health benefits.
There are several different intermittent fasting methods. The two most common are:
- The 16/8 method: Fast for 16 hours per day and eat all meals within an 8-hour window.
- The 5:2 diet: Eat normally 5 days per week and restrict calories to 500–600 on 2 days.
No matter the method, intermittent fasting split's the day or week into eating and fasting periods. This cycling between fasting and eating may influence hunger and fullness hormones, cellular repair, and other metabolic pathways in ways that promote weight loss and resilience.
Does Intermittent Fasting Cause Bloating?
Bloating is a common concern for those considering intermittent fasting. Since fasting involves long stretches without food each day, some worry it may lead to gastrointestinal distress.
Bloating refers to a feeling of fullness and tightness in the abdomen. It often occurs due to excess gas production or disturbances in the movement of food and gas through the intestines.
Bloating may be caused by:
- Swallowing air when eating or drinking
- Gas production from undigested carbohydrates
- Constipation
- Food intolerances
- Overgrowth of bacteria in the small intestine
- Inflammatory bowel diseases
Does intermittent fasting contribute to bloating by any of these mechanisms? Let's take a closer look.
Swallowing Air
Eating or drinking too quickly can cause you to swallow air, which leads to bloating when it gets trapped in your digestive system. However, there is no evidence that intermittent fasting causes you to swallow more air.
If anything, having fewer meals per day may reduce air swallowing, compared to grazing on small meals constantly throughout the day.
Gas Production
Gas production is a major cause of bloating. Most of your gas comes from two sources:
- Swallowed air: As discussed above, air swallowing while eating and drinking can get trapped as gas in your belly.
- Gas production: Your gut bacteria produce gases like hydrogen, methane, and carbon dioxide as they ferment undigested carbohydrates.
Intermittent fasting is unlikely to affect gas production. It does not cause you to swallow more air. Nor does it increase the amount of undigested carbs that reach your large intestine.
If anything, limiting eating to set times during the day may enhance digestion by allowing the gut to fully clear out between meals.
Constipation
Constipation refers to infrequent, difficult, or incomplete bowel movements. It commonly leads to bloating.
Limited studies suggest intermittent fasting does not appear to cause constipation or other adverse effects on bowel function, compared to normal eating patterns (1).
As long as you eat sufficient fiber and stay hydrated during your eating window, intermittent fasting is unlikely to promote constipation or related bloating.
Food Intolerances
Food intolerances occur when your body lacks enzymes or has sensitivities to properly digest certain foods. Lactose intolerance is one common example.
Eating foods you cannot properly digest allows gut bacteria to ferment them. This produces excess gas, leading to bloating and other digestive complaints.
However, there is no evidence that intermittent fasting provokes food intolerances or increases susceptibility to associated bloating.
If you already have food intolerances, you can avoid problematic foods whether you are intermittent fasting or not.
SIBO
Small intestinal bacterial overgrowth (SIBO) refers to excessive bacteria in the small intestine. It creates gas as these bacteria ferment carbohydrates.
Studies show an association between bloating and SIBO, although a direct causal relationship has not been proven. Population studies estimate SIBO may account for 54–90% of chronic bloating cases (2).
There is no evidence that intermittent fasting promotes SIBO or an overgrowth of gas-producing gut bacteria. If anything, giving your gut a rest from digestion during the fast may benefit the balance of your microbiome.
IBD
Inflammatory bowel disease (IBD) refers to chronic inflammation conditions like Crohn's disease and ulcerative colitis. They frequently cause abdominal pain, bloating, and other symptoms.
There are no studies examining intermittent fasting for IBD. However, animal research suggests it may have anti-inflammatory effects and other benefits for gut health (3, 4).
Overall, there is no evidence that intermittent fasting increases inflammation or worsens IBD.
Tips to Prevent Bloating While Intermittent Fasting
Research to date suggests intermittent fasting does not inherently cause bloating as a side effect. However, some simple diet and lifestyle changes may further reduce chances of bloating:
Eat Slowly
Eating or drinking too quickly introduces air into your digestive tract, which can lead to bloating. Be mindful to eat slowly and chew thoroughly during your eating window.
Choose Low FODMAP Foods
FODMAPs are fermentable carbs that can cause gas and bloating issues for some people. Focus on low FODMAP foods like rice, quinoa, oats, leafy greens, chicken, fish, and eggs.
Increase Fiber Gradually
Sudden increases in fiber intake can cause gas and bloating. If upping your fiber intake, increase it gradually over a few weeks.
Stay Hydrated
Dehydration exacerbates constipation and bloating. Drink plenty of water, herbal tea, or other non-caloric beverages during your fasting window.
Take a Walk After Eating
Light activity like walking after eating may help food move through your digestive tract to prevent gas buildup.
Limit Salt
Excess sodium causes your body to retain water, which can worsen bloating. Limit high salt foods when intermittent fasting.
Manage Stress
Stress affects gut function and may trigger bloating. Try meditation, yoga, or deep breathing to relax during fasting periods.
Get Enough Sleep
Not getting enough sleep negatively affects digestive health. Aim for 7-9 hours per night.
Avoid Chewing Gum
Chewing gum causes you to swallow excess air, which can get trapped as gas and bloating. Avoid gum, especially mint varieties.
Take a Probiotic
Probiotic supplements support healthy gut bacteria and may reduce bloating. Ask your doctor if probiotics may be beneficial.
When to See Your Doctor About Bloating
Occasional mild bloating is common and not a cause for concern. However, you should seek medical advice if you experience:
- Severe or persistent bloating
- Bloating that worsens over time
- Bloating along with diarrhea, constipation, or other disruptions in bowel habits
- Bloating that does not resolve with lifestyle changes
- Unintended weight loss
- Blood in your stool
Persistent or worsening bloating may be a sign of an underlying medical condition requiring treatment, such as:
- Food intolerances like lactose or gluten intolerance
- SIBO
- IBD like Crohn's or ulcerative colitis
- Celiac disease
- Diverticulitis
- Certain cancers
If you experience concerning bloating symptoms, make an appointment with your healthcare provider. They can help diagnose any underlying cause and provide appropriate treatment.
Tests for Bloating
If you have bothersome bloating, your doctor may recommend tests to pinpoint the cause. These may include:
- Blood tests: To check for celiac disease and other autoimmune conditions
- Stool test: To look for blood, infectious organisms like parasites, levels of inflammation, and other markers
- Breath test: You ingest a carbohydrate solution and exhale into bags to measure hydrogen and methane gas production to diagnose SIBO
- Endoscopy: A small camera on a flexible tube is inserted into your digestive tract to visually inspect for damage, inflammation, ulcers, polyps, etc.
- Imaging tests: Abdominal X-rays, CT scan, or MRI to check for structural abnormalities
Based on test results, your doctor will advise on any necessary dietary changes, medications, probiotics, elemental diet, or other therapies to reduce bloating.
Takeaway
Intermittent fasting does not inherently cause bloating as a side effect. You can take simple steps like eating slowly, limiting salt and gas-producing foods, staying hydrated, and managing stress levels to prevent bloating when fasting.
See your doctor if you experience severe, persistent, or worsening abdominal bloating to rule out any underlying medical conditions requiring treatment.
FAQs
Does intermittent fasting cause bloating?
There is no evidence that intermittent fasting inherently causes bloating as a side effect. Studies show it does not appear to promote constipation, food intolerances, gut inflammation, or other common causes of bloating.
How can I prevent bloating when intermittent fasting?
Tips to reduce bloating when fasting include eating slowly, limiting FODMAPs and salt, staying hydrated, taking a walk after meals, managing stress, getting enough sleep, and avoiding gum.
Should I take a probiotic for bloating while intermittent fasting?
Probiotic supplements may benefit digestive health and reduce bloating for some people. Talk to your doctor about whether probiotic use is appropriate.
What causes bloating if not intermittent fasting?
Common causes of bloating include swallowing excess air, gas production from undigested carbs, constipation, food intolerances, SIBO, and IBD. Lifestyle factors like stress can also play a role.
When should I see a doctor for bloating?
See your doctor if you have severe, persistent, or worsening bloating, especially if accompanied by other symptoms like weight loss or blood in stool. They can check for underlying conditions requiring treatment.