What Gut Health Means and How Fibre and Probiotics Fit In

What Gut Health Means and How to Support It

Gut health refers to the community of microorganisms living in the digestive system and how effectively your gastrointestinal tract functions. NCCIH says many of these microorganisms are helpful: some bacteria help digest food, destroy disease-causing cells or produce vitamins. The sources used here point to two practical steps: eating enough fibre and, for specific problems, probiotics.

UK government guidelines recommend that adults consume 30g of fibre each day. Most adults average about 20g a day. The NHS says fibre can help with your digestion and prevent constipation. For antibiotic-associated diarrhea, NCCIH says probiotics have shown promise, and for irritable bowel syndrome the NHS says there is some evidence they may help ease some symptoms.

Probiotics carry more risk for some people. NCCIH says the risk of harm is greater in people with severe illness or compromised immune systems, and the NHS says to talk to a doctor before taking probiotic supplements if you have an existing health condition or a weakened immune system.

The Human Microbiome and Helpful Microorganisms

The human microbiome consists of the community of microorganisms that lives on and inside the human body. Between 2007 and 2016, the National Institutes of Health (NIH) supported the Human Microbiome Project, which mapped the normal microbial populations residing in healthy individuals. Researchers are studying interactions between components of food and microorganisms in the digestive tract.

Many microorganisms are beneficial rather than harmful. Some bacteria help digest food, destroy disease-causing cells or produce vitamins. Many of the live microorganisms packaged into commercial products are identical or closely related to the microbes that naturally inhabit the human body. For how food nutrients are absorbed, see our breakdown of food nutrient absorption.

Prebiotics are nondigestible food components rather than live organisms, so they are a different thing from probiotics. Synbiotics combine the two. These distinct categories should not be conflated when evaluating commercial nutrition claims.

What Clinical Evidence Shows for Probiotics

NCCIH says probiotics have shown promise for some specific conditions, and the NHS says there is little evidence to support many of the health claims made about them. The NHS says there are many types of probiotic with possibly different effects, and a type that helps one problem does not mean it helps others.

According to the NCCIH, probiotics have shown promise for:

• Preventing antibiotic-associated diarrhea, including diarrhea caused by Clostridioides difficile. Readers managing this issue can find detailed guidance in our review of gut health after antibiotics.
• Preventing necrotizing enterocolitis and sepsis in premature infants (see the premature-infant safety warning below).
• Treating infant colic.
• Treating periodontal disease.
• Inducing or maintaining remission in patients diagnosed with ulcerative colitis.

A 2018 review of 53 studies involving 5,545 participants concluded that probiotics may have beneficial effects on global IBS symptoms and abdominal pain. However, researchers noted that it was impossible to draw definitive conclusions or identify which species, strains, or combinations are most likely to provide relief. For Crohn's disease, a 2014 review of 14 studies covering 746 participants found no evidence of benefit from probiotics, prebiotics, or synbiotics. The NHS says there is some evidence probiotics may help ease some IBS symptoms, but little evidence to support many health claims made about them.

Probiotic Product Quality, Regulation, and Safety Risks

The NHS says probiotics are generally classed as food rather than medicine. They do not go through the rigorous testing medicines do. NCCIH says many probiotics are sold as dietary supplements, which do not require FDA approval before marketing. Labels may make structure or function claims without FDA approval but cannot make disease-risk-reduction claims without FDA consent, and a probiotic marketed as a drug must be proven safe and effective in clinical trials and FDA approved.

The NHS warns that buyers cannot always be certain that a retail product contains the exact bacteria listed on the label, provides a sufficient bacterial count to exert an effect, or contains bacteria that survive long enough to reach your gut. The NHS says there is likely a huge difference between pharmaceutical-grade probiotics in clinical trials and the yoghurts and supplements sold in shops.

Safety considerations also differ depending on an individual's immune status:

• Healthy individuals: The NHS says probiotics appear safe for most people and should not cause unpleasant side effects with a healthy immune system; NCCIH reports a long history of apparently safe use in healthy people but few detailed safety studies.
• Severe illness or weakened immunity: The NCCIH cautions that the risk of harm is greater in people with severe illness or compromised immune systems. Possible harms include infections, harmful substances produced by the probiotic, and transfer of antibiotic resistance genes.
• Infant warnings: NCCIH reports that severe or fatal infections have been reported in premature infants given probiotics, and the US Food and Drug Administration (FDA) warned providers in 2023.

NCCIH reports the following survey figures on use. The 2012 National Health Interview Survey reported that approximately 4 million American adults (1.6 percent) had consumed probiotics or prebiotics within the previous 30 days. Probiotics or prebiotics were the third most commonly used dietary supplement other than vitamins and minerals, and adult use quadrupled between 2007 and 2012.

Daily Dietary Fibre Targets and High-Fibre Foods

The NHS says most of us need to eat more fibre, and that choosing foods with fibre can help with your digestion and prevent constipation. The NHS says eating plenty of fibre is associated with a lower risk of heart disease, stroke, type 2 diabetes and bowel cancer. For a related diet, read our guide on prediabetes diet strategies.

Official UK government guidelines establish the following daily fibre intake targets:

• Adults: 30g per day, compared to the current average adult intake of roughly 20g per day.
• Children aged 11 to 16: Approximately 25g per day.
• Children aged 5 to 11: Approximately 20g per day.
• Children aged 2 to 5: Approximately 15g per day.

High-fibre foods have 6g or more of fibre per 100g. The NHS advises getting fibre from a variety of sources. The NHS suggests selecting higher-fibre breakfast cereals such as porridge oats, shredded whole wheat, or plain wholewheat biscuits. Options include wholemeal bread, granary bread, wholewheat pasta, bulgur wheat, and brown rice.

The NHS also lists plenty of vegetables and potatoes with their skins on. Pulses include beans, lentils and chickpeas. Fresh or dried fruit both count; dried fruit is sticky and raises tooth-decay risk, so the NHS says it is best with a meal. For snacks, choose oatcakes, rye crackers, unsalted nuts, seeds, or raw vegetable sticks. For comprehensive strategies on scaling daily intake safely, see our guide on fiber maxing.

For more on food and blood sugar, review our guide to how food affects blood sugar.