Your gut health plays a big role in your overall health. That’s because about 70-80% of your immune cells live in your gut, so your gut microbiome influences your overall immune function. Your gut microbiome is the community of microorganisms (such as fungi, bacteria, and viruses) that live in your gut. Your gut microbiota—the specific microbes in your gut—change in response to factors like diet and exercise.
Your gut also directly communicates with your brain, and vice versa, via the gut-brain axis. This connection means that your brain can influence intestinal activities (such as having nervous diarrhoea) and in turn your gut can influence your mood, cognition, and mental health—positively or negatively.
In addition, a weakened gut can allow bacteria and inflammatory substances to be absorbed from your gut into your bloodstream. This can trigger illnesses and full-body inflammation, which is linked to an increased risk of chronic disease. Therefore, what you feed your gut is crucial to your physical and mental well-being. Here are foods and food groups that maximize the functioning of your gut and its microbiome, and a short list of foods to minimize for optimal gut health.
Pulses support good gut health. In addition to their plant protein and polyphenol antioxidants, pulses contain non-digestible carbohydrates (NDCs), including soluble and insoluble fiber. NDCs act as prebiotics, which means they serve as food sources for beneficial, health-protective microbes in the gut. When NDCs are fermented by bacteria in the gut, anti-inflammatory compounds called short-chain fatty acids (SCFAs) are produced. Polyphenols from pulses also have anti-inflammatory effects and serve as additional prebiotics.
The anti-inflammatory impact of pulses in the gut has been shown to improve the health of the digestive tract, improving its strength as a barrier between the gut and the bloodstream. A healthy gut barrier selectively allows beneficial substances into the blood, like nutrients and water. An impaired or weak intestinal barrier can allow harmful substances into your blood circulation that can result in systemic or full-body inflammation, which is linked to illnesses and disease. SCFAs in particular play a key role in maintaining the health of your intestinal barrier.
- Dry peas (like split peas and black-eyed peas)
- Probiotic Foods
Probiotics are live microorganisms that have been shown to help reshape the makeup of your gut microbiota in ways that can enhance your immune function, help reduce obesity and diabetes risk, promote overall wellness, and improve multiple bowel diseases. Probiotics change the gut environment in ways that decrease the ability of harmful bacteria to grow and allow healthful bacteria to flourish.
Probiotics may be found in non-pasteurized fermented foods, such as raw sauerkraut. Multiple studies have shown that microorganisms in fermented foods can survive digestion and reach the colon, where they can help support immune function.
A 2021 Stanford University study assessed 36 healthy adults who were randomly assigned to 10-week diets that included either fermented foods or high-fiber non-fermented foods. Compared to the high-fiber eaters, those who consumed fermented foods experienced greater benefits, including positive immune status changes and reductions in levels of 19 inflammatory proteins, including one called interleukin 6, which has been linked to conditions such as rheumatoid arthritis, type 2 diabetes, and chronic stress.
Researchers concluded that the study results suggest that fermented foods may have a powerful impact on immune function and may help combat non-communicable chronic diseases (NCCDs), such as obesity and diabetes, which are largely driven by chronic inflammation.
Probiotic foods may include:
- Fermented vegetables
Prebiotics help feed probiotic bacteria in your gut by boosting the growth of “good” bacterial strains, including Bifidobacterium and Lactobacillus. They also shift the intestinal pH, which prevents harmful microbes from growing, such as Clostridium perfringens and Escherichia coli.
These changes result in reduced gut inflammation and are thought to increase the production of a hormone called intestinal glucagon like peptide 2 (GLP2), which is known to reinforce the strength of the gut lining. In addition, the fermentation of prebiotic fibers, which leads to the production on SCFAs, has been shown to reduce hunger and improve the post-meal regulation of blood sugar and insulin levels. SCFAs have also been shown to reduce inflammation and have a positive impact on cholesterol regulation.
A typical Western diet, which is typically low in vegetables, fruits, and whole grains, provides only 1-4 grams of prebiotics per day compared to the 5.5-20 grams per day shown to offer benefits in research studies.
Food sources of prebiotics include:
- Bananas (especially when less ripe)
- Jerusalem artichokes
- Wheat bran
Foods Rich in Polyphenols
Some plants produce antioxidants called polyphenols. These natural compounds protect plants from damage and illness as they grow. In the human body, polyphenols are linked to heart and brain protection. In addition, research shows that the gut microbiome converts polyphenols into bioactive compounds that get absorbed into the bloodstream and have therapeutic effects within the body.
It’s estimated that 5–10% of total polyphenols are absorbed from the small intestine into the bloodstream. The remaining 90-95% accumulate in the large intestine where they have prebiotic effects that positively shift the balance of “good” and “bad” gut microbes. The breakdown of polyphenols within the gut is also linked to immune support and colorectal cancer prevention.
Polyphenol-rich foods include:
Avocado consumption has been linked to a variety of beneficial health outcomes, including improved weight management and protection against heart disease. A 2021 study found that this fruit with good fat also provides gut health benefits.
Researchers randomly assigned 163 adults with overweight or obesity to one of two groups for 12 weeks. Participants ate one meal per day (breakfast, lunch, or dinner) with or without avocado. The study subjects provided blood, urine, and fecal samples throughout the study.
Scientists found that the avocado eaters developed a greater abundance of gut microbes that break down fiber and produce beneficial SCFAs. They also developed a more diverse array of healthful gut microbes compared to people who did not eat the avocado meals. And while the avocado group consumed slightly more calories, they had more fat in their stool, which means they absorbed less fat from their digestive tracts into their bloodstreams. Researchers say this is the first study to evaluate the effects of avocado consumption on human gut microbiota in the absence of a caloric restriction, which eliminates calorie change as a factor in the changes observed.
Foods to Limit for Gut Health
Some foods have been shown to negatively impact the health of the gut and its microbiota. Limit or avoid these foods to optimize gut health.
Research shows that an amino acid called L-carnitine from red meat is metabolized by gut microbes into a compound called trimethylamine-N-oxide (TMAO), which is linked to artery hardening and increased heart disease risk factors. Processed red meat consumption (bacon, sausage, pepperoni) may also increase levels of microbes in the gut that increase inflammation and up the risk of colorectal cancer.
Ultra-processed foods are defined as industrially manufactured ready-to-eat or ready-to-heat formulations containing food additives and little or no whole foods. Examples include soft drinks, fast food, chicken nuggets, hot dogs, and sweets. A high consumption of these foods is associated with an increased risk of heart disease and obesity.
A 2021 research review concluded that ultra-processed foods reduce the type and variety of beneficial gut microbes compared to diets rich in minimally processed plant foods. This shift promotes inflammation in the gut and increases gut permeability. As previously noted, these gut changes allow substances to be absorbed into the bloodstream that can promote full body inflammation and increase disease risk, including obesity, dementia, and Alzheimer’s.
Studies show that chronic alcohol consumption significantly alters the gut microbial community. Alcohol causes a decrease in beneficial microbes, an increase in harmful, pro-inflammatory microbes, and an increased gut permeability, which can allow pathogenic bacteria to be absorbed into the bloodstream.
While artificial sweeteners are sugar-free and calorie-free, their use has been linked to an increased risk of obesity and type 2 diabetes, and the effects may start in the gut. In experiments where gut microbiota taken from hosts who consumed low-calorie sweeteners were transferred into healthy mice, the animals developed impaired glucose tolerance. Other studies show that sugar substitutes may shift the makeup of microbes in the gut, reduce the production of beneficial SCFAs, and increase inflammation.
A Quick Review
Gut-supporting foods increase the type and number of beneficial gut microbes, reduce the growth of harmful bacteria, increase the production of anti-inflammatory compounds, like SCFAs, support immune function, and strengthen the integrity of the gut wall to keep harmful compounds out of the bloodstream.
Some foods counter these positive effects within the gut, which may lead to weakened immune function, digestive illnesses, and even increased chronic disease risk.
By: Cynthia Sass, MPH, RD