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Fast food

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Fast food is quite an obvious one, but do you know exactly why it negatively affects your gut health? One study found that fast food is linked to levels of certain bacteria in the gut, which will therefore lead to an imbalance of bacteria in the gut. Then because of this imbalance, fast food consumption was also linked to Crohn’s disease, IBS, and inflammatory bowel disease. Therefore, it is clear to see the negative impact fast food holds.

Processed baked goods

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Like fast foods, high-sugar foods are one of the leading culprits for an unhealthy gut. For a healthy gut, it’s best to avoid processed baked goods, or at least don’t eat them on a regular basis. This is because a 2020 report found that eating high-sugar foods can create more proteobacteria and will decrease your levels of Bacteroidetes, which causes an imbalance in your microbiome. Then, because of these disruptions, this will lead to an increased risk of low-grade inflammation.

Overly salty foods

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Too much sugar is guaranteed to impact your gut in a bad way. This is because many researchers have found a link between the gut microbiome and hypertension, which is high blood pressure. It has also been found that diets with higher levels of sodium can lead to increased tissue and intestinal inflammation, meaning too much sodium may alter the gut microbiome.

Red meat

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Most people have heard about red meat can increase the risk of heart disease, however not many know about the numerous health issues it can cause your gut health. A study consisting of 3,931 participants all above the age of 65 has found that over 12.5 years, those who had a daily consumption of red meat increased the risk of heart disease by 22%. This increased risk was linked to the gut microbiome which was altered by red meat.

Artificial sweeteners

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Many people reach for artificial sweeteners to save calories and help weight loss, however they can negatively affect your gut health over time. It was even found that the consumption of artificial sweeteners may be linked to developing a gluten intolerance because of the ways it can alter your gut microbiota. It was also found that it can cause damage to the lining of your gut and increase its permeability.

Processed meats

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Of course processed meat is a great source or protein, however meats like bacon or sausage have been known to potentially cause problems for your gut health due to all of its saturated fat content. A review found a link between the total fat intake (specifically saturated fats) and a reduction in total bacterial number, richness and diversity in the gut. These are all clear signs of poor gut health.

Soybean oil

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Soybean oil is everywhere, it can be found in margarine, certain salad dressings, mayonnaise, nutrition bars and many frozen foods. A study, however, found that it may be harmful to your gut health. This is because it was noted that a diet high in soybean oil, which is rich in omega-6 fatty acids, decreased levels of 2 bacterial species (faecalibacterium and blautia), which then produces health-promoting metabolites and are related to imbalanced glucose metabolism.


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The effects of sugar don’t stop at food. Sugary drinks like soda can also cause immense problems for your gut health, especially when they’re consumed on a regular basis. According to a review, sugar-sweetened beverages are associated with an imbalance of certain bacteria in the gut. Therefore, the leading explanation for this connection has to do with the way added sugar can erode the gut barrier and cause greater levels of gut permeability.


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Of course, drinking every now and again is fine, however heavy drinking can have lasting effects on your gut health. Certain alcoholic drinks have been shown to disrupt normal digestion and it’s also been found that moderate to heavy drinkers actually have fewer healthy bacteria colonies in their digestive system. Therefore, drinking regularly can alter gut diversity, increase permeability and increase inflammation.

Juices with added sugar

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Like soda, sugary juices can also wreak havoc on your gut health. This is because of the large amounts of added sugar within them, especially the store-bought juices which have excess added sugar – natural juice made from 100% fruit is fine. A recent study on mice showed that too much sugar can lower the amount of immune cells in the body, as well as create a larger imbalance in the gut microbiome.


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Perhaps you think of peppermint as a stomach-settler. For some people, it’s exactly this. For others, it’s a prime cause of acid reflux. This is unpleasant to experience and, if it happens frequently enough, may damage the enamel on the teeth. Peppermint causes acid reflux by relaxing the muscle at bottom of the esophagus, allowing the acidic stomach contents to travel upwards.

Fried foods

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Thanks to their high fat content, fried foods are an easy shortcut to an unpleasant bout of diarrhoea, especially for those people not used to food cooked in this way. Air frying, grilling and even roasting are all healthier alternatives that are less likely to upset your gut.

Citrus fruit

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Yes, citrus is high in Vitamin C but it’s also a common cause of an upset stomach. It’s the combination of relatively high fiber levels (in fruit, not juice) and very high acidity that does the damage. If you’re prone to problems, approach citrus fruit with caution and perhaps consider getting your daily Vitamin C dose from broccoli or other leafy greens.


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In its pickled form, cabbage is widely considered to be one of the best things you can eat. However, raw, unpicked cabbage is often hard to digest thanks to its high fiber content. For some people, this results in gas and painful bloating. Cooking the cabbage may reduce this problem.

Dairy products

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If dairy products give you gas, bloating and diarrhea, you may be lactose intolerant. This isn’t a true allergy but means that you lack the enzymes needed to digest the protein in milk and other dairy products. It’s a very common problem in adults as, like most mammals, the majority of humans lose the ability to digest milk effectively as they grow out of babyhood.

Too much fiber

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Although around 95% of people are risking their health by not eating enough fiber, consuming too much isn’t great for you either. Eating more than the recommended daily amount may cause bloating, flatulence, abdominal pain and diarrhoea. In people with Crohn’s Disease, too much fiber can even cause an abdominal blockage.


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One of the ultimate comfort foods, chocolate’s many virtues don’t include being easy on the digestive system. Its caffeine and theobromine content relax the sphincter at the bottom of the esophagus, which can allow the acidic stomach contents to travel upwards and cause heartburn. Meanwhile, its high fat levels slow digestion, which can increase pressure in the stomach and, again, contribute to heartburn.


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True wheat allergies are rare. However, many more people suffer from a wheat intolerance. This means that they struggle to digest wheat and experience consequential symptoms that may include bloating, abdominal discomfort, flatulence and altered bowel habits. Reducing wheat intake can help, as can opting for wheat products, like sourdough, that use fermented grains as these are easier to digest.

Spicy food

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It’s fairly common for spicy food to cause heartburn, abdominal discomfort or even an upset stomach. Anyone already prone to dyspepsia should take particular care: it’s thought that spicy food can worsen the condition. Other people may be sensitive to capsaicin, a common ingredient in many spicy meals. This can irritate the gut lining and also have a laxative effect.


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Gluten is a protein found in wheat, barley and rye. Some people have a condition in which their immune system attacks their own body when they eat anything containing this protein. This is celiac disease. Symptoms include bloating, abdominal pain, diarrhoea and fatigue. Itchy rashes, nerve damage, weight loss and fertility problems are also common in sufferers. Treatment is to avoid eating anything containing gluten.


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Although generally very good for the digestive system and overall bodily health, beans cause digestive issues in some people. The problem stems from the body’s inability to break down oligosaccharides, a type of sugar found in beans. This is why, famously, beans cause flatulence – and, in some people, the symptoms are more severe and less easy to tolerate.


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Another surprising trigger of heartburn, coffee can irritate the sensitive valve at the top of the stomach. This can result in the some of the acidic contents from the stomach travelling back up the esophagus, causing a burning sensation that it sometimes mistaken for a heart attack. If the acid reaches the back of the mouth, it may damage the teeth.

Factory farmed meat

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From the animals’ perspective, factory farming is a stressful way to raise livestock. Over-crowding and market pressure means that most factory farmed meat contains traces of the antibiotics and, sometimes also, growth hormones given to the animals. Over-use of antibiotics contributes to microbial antibiotic resistance. As a result, eating factory farmed meat risks the health of the human gut microbiome.

Refined grains

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Refined grains are those found in white flour, white bread, white rice, and most bakery treats. Stripped of most of their fiber, these grains are little better than sugar. As such, they’re digested in the first part of the small intestine. This raises blood sugar and leaves nothing for gut microbes further on the intestine. In some people, this unsatisfactory process also results in diarrhea.

Farmed fish

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Farmed fish are often raised in surroundings inadequate for their own health – and this has implications for the human consumer. First, traces of antibiotics in the fish can affect the microbial flora in the human gut. Secondly, some species contain high levels of mercury. This has several health implications for human consumers, including a possible reduction in beneficial bacteria within the digestive system.


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Unfortunately, pizza’s tastiness isn’t matched by its health properties. Refined white flour, high levels of saturated fats and, frequently, sizeable quantities of sugar all affect the gut’s ability to do its job. Choosing pizza with dough made from whole grains, homemade tomato sauce with minimal or no sugar, and being abstemious with the cheese can help make it easier on the digestive system.

Salad dressing

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Many commercial salad dressings are high in FODMAPS. These are the short-chain carbohydrates that the small intestine struggles to digest. In sensitive individuals, this can cause gastric symptoms. Good alternatives include homemade dressings made from combinations of olive oil, lemon, honey, Dijon mustard, mint, apple cider vinegar and coconut youghurt.


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On one hand, eating tomatoes is good for gut health because they promote the growth of “good” gut microbes. On the other, tomatoes are acidic, which can upset some people’s stomachs. Additionally, some people are sensitive to the nightshade family – which includes tomatoes. Associated symptoms include heartburn, nausea, gas, bloating, diarrhoea and vomiting.

Tomato ketchup

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As a highly acidic foodstuff, it’s common for ketchup to cause heartburn in susceptible individuals. Adding a pinch of baking soda or even sugar reduces the ketchup’s acidity and may make it more tolerable. However, it’s best to avoid it entirely if you’re prone to heartburn.


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Among its many vices, sugar in any form has a detrimental effect on the digestive system. This is because sugar feeds some of the less helpful bacteria in the human gut. And, if these bacteria are allowed to crowd out the “good” bacteria, you may start to experience increasing problems with digestion.

GMO food

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The effect of GMO food on the human body is still unclear. However, one school of thought suggests that the artificially-modified genes could transfer into the bacteria within the human gut, affecting their function. Another concern relates to the potential effects for the gut biome of the herbicides routinely used on GM crops.

Onion and garlic

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Onions and garlic are both flavorsome and aromatic. However, they’re frequently also hard to digest. In sensitive individuals, the results can include cramping and gas. Raw onions and garlic usually prompt more severe symptoms but the cooked versions are not always problem-free. Some people may need to eliminate onions and garlic from their diet altogether. Others may get away with reducing the quantities eaten.

Tap water

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Obviously, water is essential. However, it pays to pay attention to the quality of your drinking water. Although perfectly safe from a public health perspective, tap water is treated with chlorine, which can upset the stomach. It also frequently contains traces of the antibiotics fed to farm animals – and this can negatively affect your own gut’s biome.

Cereal bars

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They sound healthy but, like pretzels and other cereal-based snack foods, cereal bars aren’t the best option for optimal gut health. High in refined carbs, they are quick to digest. This can lead to a rapid spike in blood sugar and insufficient fiber for the large intestine to work effectively.


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As sweet as candy, dates have far more nutrition. They’re high in fiber, and rich in B Vitamins and other important minerals. However, they also have a tendency to upset the digestive systems of people with sensitive guts. This is mostly down to the high fiber content so, if this is a problem for you, enjoy dates in moderation only.

Brussel sprouts

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Whether you love ’em or loathe ’em, it’s true that brussel sprouts are always good for the digestive system. They contain high levels of fructans, which are polymers of naturally-occurring fructose. The gut bacteria naturally ferments fructans and, in sensitive individuals, this can cause abdominal discomfort.


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Although definitely worth including in the average diet, a couple of potential health concerns affect eggs. The first is the risk that they – or their shells – are contaminated with the salmonella bacterium, which can cause a severe upset stomach. The second concerns residual traces of antibiotics, which can affect human gut health.


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Mushrooms are rich in a sugar alcohol called mannitol. Some people can eat mushrooms – and, hence, mannitol – with no adverse effects but others suffer gut irritation. Sometimes, temporarily cutting out mushrooms from the diet and making an effort to improve overall eating habits is sufficient to permit the reintroduction of small quantities of mushrooms.

Saturated fats

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The health risks of saturated fats are well documented. However, aside from their implications for heart and arterial health, cancer risk profile, and weight, eating too much of them also change the microbial flora in the gut. Generally, this means more bilophila – a type of microbe that breaks down the bile that’s needed to digest high-fat food. Unfortunately, bilophila also frequently causes gut inflammation.


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Whether you enjoy them freshly picked, cooked into a cobbler or made into jelly, it’s worth knowing that blackberries are full of sorbitol. This is a type of carbohydrate that’s also called a “sugar alcohol”. Although not a problem for most people, sorbitol can sometimes cause bloating, gas, stomach pains and diarrhoea.