An upset stomach, bloating, constipation, fatigue, skin irritation, a weak immune system and food intolerances are all signs of poor gut health. Our gastrointestinal system is incredibly complex and requires a delicate balance in order to function properly.

You might have heard of the gut microbiome, but if not, it refers to the bacteria and microorganisms (also known as microbes) that live in your stomach and intestines. It’s thought that each individual has between 300-500 different species in their microbiome. Some of these are extremely beneficial and play an important role in digestion and our overall health, known as good gut bacteria. Some are very harmful, called bad gut bacteria.

Most of the time, there’s around 85% good bacteria and 15% bad bacteria in your microbiome, and this is fine as the good can counteract the bad. It’s when this balance of bacteria is disturbed and the bad bacteria increases that you may start to feel unwell.

Find out how to keep your good gut bacteria in abundance by discovering our 15 worst foods for gut health and why you should avoid them.

The 15 Worst Foods for Gut Health


a piece of red meat on a wooden cutting board

1. Red meat
Red meat contains a compound called carnitine which, when digested, produces a type of gut bacteria that transforms into trimethylamine-N-oxide, or TMAO. TMAO can lead to a buildup of plaque in the arteries, which can cause them to become clogged and increase the likelihood of cardiovascular diseases. As well as increasing the amount of plaque in your arteries, diets high in red meat can also decrease the good bacteria. Be kind to your gut by opting for leaner protein like chicken, fish or beans and pulses.

2. Eggs
Like red meat, eggs also contain a protein compound that encourages the growth of a specific gut bacteria. This gut bacteria then produces a chemical that increases the chance of plaque clotting the arteries, raising the risk of a heart attack or stroke.

3. Dairy
In the UK, between one and two people in every 10 suffer from lactose intolerance. It’s a common problem where many people lack the enzyme lactase, which is needed in order to break down lactose found in cows’ milk. It can cause uncomfortable symptoms like bloating, diarrhoea and cramps.

Some people are more sensitive to lactose than others, but regardless of whether your body can break down lactose or not, it has significant effects on your gut microbiome. And the fast-acting effects of lactose mean that these effects occur in your body within a few days.

a load of bread on a wooden board

4. Gluten
Gluten is another type of protein that’s found in most grains, like wheat, rye, and barley. Similarly to lactose, some people are more sensitive to the effects of gluten than others and have celiac disease. For those who suffer from celiac disease, gluten can trigger a number of side effects in the gut, such as aching, cramps, bloating, indigestion and constipation. It can also damage the small intestines. Even if you don’t have celiac disease, consuming gluten can have drastic and long-term impacts on your gut bacteria.

5. Antibiotics
The use of antibiotics at home is extremely common. They’re often used to fight against infections and illnesses by killing the bad bacteria or stopping them from multiplying, but this means that they can also kill the good gut bacteria and affect your gut flora in the long-term.

After one course of antibiotics, your levels of good bacteria are temporarily reduced. Eventually, after one to four weeks, your body will replace the ones you lost, however your body won’t be able to produce as many as you had before.

Before changing your current antibiotic intake, always consult your doctor, and only limit your intake if it’s safe to do so. This may help to reduce the level of antibiotics you consciously consume, however, antibiotics are also present in many animal products like meat, poultry and fish.

This is because farmers often use antibiotics to prevent their animals from getting infections. The antibiotics that they feed their livestock, are still present in the animal products that we then consume. This accumulation of secondhand antibiotics has the same effect as if we were directly consuming the antibiotics. What’s worse is that some bacteria can grow resistant against the use of antibiotics, leading to even more dangerous bugs and illnesses that can be passed on to us.

6. Alcohol
Alcohol has been found to affect the microbiome by causing dysbiosis, an imbalance of bacteria in your gut, and encouraging the growth of bad gut bacteria. If consumed in excess, it can also inflame the stomach lining.

While any type of alcohol consumed in excess will have negative effects on your health, some alcohol can be better than others.

In a study that compared the effects of red wine and gin on gut health, gin was found to decrease good gut bacteria whereas red wine actually increased the amount of good gut bacteria. The study suggested that a moderate amount of red wine can actually be beneficial. This is due to the plant compound polyphenol found in red wine, which can be broken down and may have a protective effect on good gut bacteria.

a deep fat fryer with chips frying in oil

7. Fried foods
Fried foods that are cooked in oil, also absorb a lot of the oil that they are prepared in. These heated oils are harder for the body to digest as the oils can irritate the stomach and cause stomach pain, gas, heartburn or acid reflux. As well as the uncomfortable side effects of fried food, they can also encourage the growth of bad gut bacteria and damage the good.

As the amount of good bacteria is reduced in your gut, this causes a lack of gut diversity. A lack of gut diversity means that your microbiome is missing a range of bacteria that help it perform at its optimal standard. The higher your gut diversity, the better your health and vice versa.

If you’re cooking with oil, choose alternative oils like coconut or avocado oil as they don’t break down into harmful compounds when heated.

8. Artificial sweeteners
Artificial sweeteners like saccharin, sucralose and aspartame are often found in “diet-friendly” drinks as they contain no sugar or calories. Don’t be fooled, these sweeteners can wreak havoc on your gut, changing the gut microbiota balance and altering the microbiome.

And it’s not just artificial sweeteners to watch out for. Any form of sugar, white, refined or even natural, can have a negative impact on your gut. This is because sugar breaks down in the body and feeds the bad gut bacteria. The more sugar consumed, the more the bad bacteria can grow and flourish. Sugar can also create dysbiosis and lead to an excess growth of yeast.

9. Fizzy drinks
Fizzy drinks are notorious for the amount of sugar and artificial sweetener they contain, making them one of the worst foods not only for gut health, but general health. Alongside the side effects listed in our last point, fizzy drinks are also carbonated, which can cause bloating.

a frying pan with bacon sizzling in oil

10. Processed and refined foods

Processed and refined foods are hard to summarise as they contain such a wide range of food types, however their effects can be outlined due to the lack of diversity in their ingredients. For example, most processed or refined foods lack a range of nutrients and are instead padded out with sugars, salts, artificial sweeteners, additives and preservatives. All of these chemical compounds can be broken down to feed the bad gut bacteria.

The lack of diversity also means that your microbiome isn’t getting the range of microbes it needs from organic, natural foods to feed the good gut flora.

11. Soy
If you’re thinking about swapping out your red meat intake for soy instead, check that it’s the whole food version and not a soy protein isolate that you’re adding to your meals. Soy is made from soybeans, which are an excellent source of probiotics that feed the good gut bacteria.

But many soy products nowadays are heavily processed or genetically modified, which turn this gut-friendly food source into a food to avoid.

These processed versions of soy can be harmful to two strains of good bacteria that are vital for microbial health and a balanced gut.

Always try to pick organic soy food products, especially ones that are fermented like tempeh or miso. These are microbiome-friendly and your gut will definitely thank you for them.

12 Corn
It’s common knowledge that our body cannot digest corn. We can still reap the nutrients from it, but due to its high cellulose content, it cannot be fully broken down in the body. Instead, it passes through the intestines and can cause uncomfortable side effects like cramps, abdominal pain and gas.

sliced grapefruit and orange citrus fruits

13. Citrus fruits
Citrus fruits like oranges, grapefruits and lemons all contain a high amount of acid. That’s the sting that you might sometimes feel on your tongue. Some people are more resilient to the acid in these fruits, but it can cause acid reflux in others. What’s more, the acid in these fruits can irritate and damage your stomach lining if consumed on an empty stomach and in large quantities.

14. Coffee
Coffee is known to irritate and even damage the stomach lining and can cause heartburn, acid reflux, constipation and irritable bowel syndrome.

Coffee tends to be paired with milk and sugar, two other damaging gut foods on our list. The mix of all three things can really upset the balance of your gut.

15 Nightshades
Nightshades are a family of vegetables that include tomatoes, eggplant, potatoes, bell peppers, spicy peppers and pimentos. While these are generally thought to be nutritious and an important part of a balanced diet, these vegetables all contain alkaloids. Alkaloids are natural insect repellents that can also be toxic to humans in large amounts.

For most, these vegetables will be harmless to eat. But for some people with inflammatory conditions or who are sensitive to intestinal inflammation, these vegetables are ones to avoid. Cooking these vegetables can greatly reduce the alkaloid content, but even still, they can trigger inflammation and cause great discomfort for people who suffer from arthritis or autoimmune disorders.

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