News flash: What you eat matters. Not only to your waistline, but also your insides. Your organs like you better when you opt for the salad instead of the fried cheese platter. (Although that fried cheese platter is so, so delicious.) But there are few things more important than your gut. It’s really important to keep it healthy and functioning properly. It regulates so many things, and is a big factor in how you feel. And while yes, we all know that eating healthy is important. But we’re human. And we all have our weaknesses. And that’s ok! But some diet weaknesses are worse than others. So what are some of the worst foods for gut health?
Our gastrointestinal tract and digestive system is the first step for nutrient utilization. When we take our first bite, the digestion process begins — nutrients are broken down and continue to be metabolized and absorbed as it travels throughout our GI tract. Our GI tract is made up of multiple body parts- our mouths, esophagus (throat), stomach and intestines and rectum. Which means our digestive system includes the pancreas, gallbladder and liver too.
Our intestines contain a crucial component to digestion and absorption and overall gut health: microorganisms. These include bacteria, fungi, and even viruses. These microorganisms exist in our GI tract as a microbiome. Our microbiome plays a role in our health, from immune support to metabolism. This microbiome is delicate and ever-changing. It is influenced by multiple factors: environment, genetics, medications, and diet. Chronic disruption to our microbiome and cellular damage from chronic inflammation overtime can lead to various diseases such as cancer, Irritable Bowel Syndrome (IBS) Inflammatory Bowel Disease (such as Crohns and ulcerative colitis), and type 2 diabetes.
So what are the worst foods for gut health?
Which foods can disrupt the good bacteria in our guts? Which foods can cause damage to our GI tract and increase inflammation?
1. Processed Meats
There is ongoing research on how red meat and processed meats can affect our GI health. However, the research that is currently out there shows strong evidence that processed meats can damage our gut health. Enough so that the World Health Organization declared processed meats as a Group 1 carcinogen for humans, meaning there is sufficient evidence that it causes cancer in people, especially colorectal cancer.
Processed meats include multiple foods: lunch meats, bacon, hot dogs, jerky, and other cured meats. These processed meats can contain added nitrates and nitrates, which help cure the meats and keeps them fresher for longer. However, nitrites and nitrates, when ingested, react within our bodies to produce cancer-causing compounds. While they can taste great, they are one of the worst foods for gut health.
2. Alcohol
Alcohol can be fun. But it can also wreak havoc on our GI system. This doesn’t really include social drinking. Social drinking is about one drink for women and two drinks for men. The problem really starts with excessive drinking. Chronic alcohol use can cause chronic inflammation in our bodies and alter our bacteria in our GI systems. There are different processes in our body to metabolize alcohol, especially depending on the quantity of alcohol. When the body is metabolizing excessive alcohol amounts, free radicals are produced. These free radicals cause cellular damage, which can lead to disease.
The bacteria in our GI tract can also metabolize alcohol, which produces compounds that promote inflammation. Over time, chronic inflammation can cause damage to the GI system and other organs, and it can lead to different diseases. Chronic alcohol consumption can also increase risk of colon and rectal cancer, per the American Cancer Association. Excessive alcohol consumption can interfere with the absorption of certain B-vitamins such as folate and thiamine, and can cause deficiencies. It’s obvious why this is one of the worst foods for gut health out there. (Is it a food? Technically, yes.)
Alcohol can also induce acid reflux, or heartburn. There is a lever that separates our esophagus and stomach, also known as a sphincter. Alcohol relaxes this sphincter, and our acidic gastric juices in our stomach backflow into our esophagus, causing heartburn. Frequent heartburn can damage our esophagus. Overtime, this can increase our risk for esophageal cancer.
3. Fried and Greasy Foods
Fried and greasy foods are a staple in the American diet. Sadly, they are also one of the worst foods for gut health. From french fries and chicken fingers to pizza, onion rings and cheeseburgers. These foods are high in fat. Too many fatty or greasy foods at one time can overwhelm the digestive system and cause diarrhea. High fat diets can also disrupt our gut microbiome by altering the composition of bacteria in our guts. Overtime, this can produce inflammation, damage our gut’s lining, and overtime can lead to chronic disease.
We are what we eat. It is up to us to develop a healthy eating pattern that focuses on wholesome, nutritious foods. Can the foods and drinks listed above be incorporated into our diet? Of course, but enjoy on occasion. The object is to not eat these foods in excess. But this is difficult due to the nature of our Western-diets. Utilize fruits, vegetables, whole grains, lean protein and low fat dairy as a foundation for your eating pattern. These foods can help regulate and maintain a healthy gut flora, and help keep our body and health in check.
4. Artificial Sweeteners
For years the working assumption was that a sweetener with no calories was inert. It tastes sweet, it passes through, nothing much happens. That assumption has not held up well.
In 2022, researchers published a randomized controlled trial in Cell that gave 120 healthy adults saccharin, sucralose, aspartame or stevia for two weeks, at doses below the accepted daily intake. All four changed the bacteria in participants’ stool and mouths, and shifted compounds circulating in their blood. Two of them, saccharin and sucralose, significantly impaired how well people handled glucose.
The part worth knowing is that the effect was not the same for everyone. When the researchers transplanted participants’ microbiomes into germ-free mice, the mice tended to show the same glucose response as the person the sample came from. The sweetener was not acting on the body so much as on the bacteria, and your bacteria are not the same as anyone else’s.
The World Health Organization now recommends against using non-sugar sweeteners for weight control at all, on the grounds that they do not appear to reduce body fat long term.
5. Emulsifiers in Ultra-Processed Food
Look at the label on your ice cream, your salad dressing, your bread, your oat milk. Somewhere down the list you will probably find an emulsifier: carboxymethylcellulose, polysorbate 80, carrageenan. They keep things smooth and stop them separating on the shelf.
A 2022 controlled-feeding study in Gastroenterology fed healthy adults either an emulsifier-free diet or that same diet with 15 grams of carboxymethylcellulose a day for 11 days. The emulsifier group reported more abdominal discomfort after meals, and their gut bacteria lost diversity. Short-chain fatty acids, the compounds gut bacteria make out of fiber, dropped.
In two participants, bacteria started moving into the mucus layer that normally keeps them at arm’s length from the gut lining. That encroachment is one of the hallmarks of gut inflammation.
It is worth being straight about the size of this one: 16 people, 11 days. It is not proof that a scoop of ice cream will hurt you. It is notable because almost everything else we know about emulsifiers comes from mice, and this time it was people.
6. A Diet With Almost No Fiber In It
The last one is not a food you are eating. It is a food you are not.
Fiber is the one part of your diet your own enzymes cannot touch. As Harvard’s Nutrition Source puts it, dietary fiber can only be broken down and fermented by enzymes from the microbiota living in your colon. It arrives intact, and your bacteria eat it.
What they make in return are short-chain fatty acids, the same compounds that fell in the emulsifier study. Which means a diet of white bread, refined grains and very little produce is not neutral for your gut. It quietly starves the part of you that was going to do the work.
Variety appears to matter as much as quantity. The American Gut Project, which analyzed samples from more than 10,000 people, found that the number of different plants someone ate tracked with the diversity of their microbiome, while labels like vegan or omnivore had little explanatory power. Harvard’s list of foods that feed those bacteria is a good place to start: garlic, onions, leeks, asparagus, Jerusalem artichokes, bananas, beans and whole grains.
What Actually Helps
Cutting things out is only half of it, and the research on what to add is in some ways more interesting than the research on what to avoid.
A 17-week randomized trial at Stanford, published in Cell in 2021, put healthy adults on either a high-fiber diet or a high-fermented-food diet — yogurt, kefir, kimchi, sauerkraut, kombucha, fermented vegetables. The fermented-food group steadily gained microbiome diversity and saw inflammatory markers go down.
The fiber group did not, at least not within 17 weeks. Their bacteria got better at breaking fiber down, but overall diversity held steady and the trial’s main inflammation measure did not move. The researchers suggested that people starting with a less diverse microbiome may need longer, or may need the bacteria before they can make use of the fiber.
That is not an argument against fiber, which the rest of the evidence supports comfortably. It is an argument for both, and for patience. Gut bacteria turn over in days, but the composition of the whole community shifts over months.
What to Eat When You’re Cutting Back
Start with whichever meal includes processed meats the most. Maybe breakfast is all about fried foods, or lunch centers around a ham sandwich. Think about easy alternatives to the processed meats in these meals: maybe you could top your pasta with white beans instead of sausage, or make a sandwich with leftover roast chicken (or mashed up chickpeas with some fresh herbs, or egg salad), etc.
According to the World Health Organization, processed meats are those that have been salted, cured, fermented, smoked, or otherwise processed to enhance flavor or improve preservation. These include hot dogs, sausages, canned meat, corned beef, ham, jerky, etc. It is the way the meats are made, not what is written on the label, that counts.
These alternatives aren’t intended to be prescriptive, there is no one-size-fits-all way to eat, nor is there one meal that can redeem you. They just need to be practical and tasty enough for you to want to eat them and buy the ingredients again and again, which, after all, is the point.
Give Fiber a Place on the Plate
NIDDK says adults need 22 to 34 grams of dietary fiber per day depending on age and sex. Try to increase your intake of fiber-rich foods such as whole grains (oatmeal, whole wheat bread), legumes (lentils, chickpeas, black beans), fruits (berries, apples with skin), vegetables (broccoli, carrots) and nuts (peanuts, almonds).
Making changes to foods that are already part of your diet is easier than venturing out and buying foods you’ve never eaten before. Add some fiber-rich foods to your diet by adding berries to breakfast, using whole-wheat bread on your sandwich or stirring a small amount of beans into your soup.
According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the way to add dietary fiber is to do it a little at a time so your body gets used to the change. NIDDK also says to drink plenty of liquids to help the fiber work better. You don’t gain anything by trying to reach the recommended amount of dietary fiber for adults in a single sitting if you’re starting with a diet that’s low in dietary fiber. Add one thing and give your body some time to get used to that.
A Healthy Food Can Still Disagree With You
Beans and onions and certain fruits can be difficult to digest with IBS, which can make eating well seem oh-so-unfair. Keep in mind, though, that healthy and easy to digest are 2 different issues.
Just because you’re experiencing symptoms, that doesn’t mean that you’re experiencing damage. For example, bloating on its own doesn’t necessarily indicate that the food is bad for you. As the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) points out, with IBS you get those symptoms without any visible signs of damage or disease in your digestive tract. Also, a food that triggers symptoms may not necessarily need to be a food you stop eating altogether.
Diet can help with IBS for some, but not all, people, the NIDDK notes. Your doctor may suggest a low FODMAP diet, which limits certain poorly digested carbohydrates called FODMAPs, for a few weeks to see whether your symptoms improve. If they do improve, your doctor may then suggest slowly adding those foods back in to find out what you tolerate.
If certain healthy foods are problematic for you, consider working with a registered dietitian who can suggest options to keep from continually limiting your diet.
With Reflux, Timing Deserves Attention Too
If you often have reflux symptoms at night or when you lie down, NIDDK says that symptoms may be helped by eating meals at least 3 hours before you lie down or go to bed.
NIDDK lists high-fat foods and alcoholic drinks as foods and drinks that are commonly associated with reflux symptoms. However, it is important to talk with your doctor about what might be causing your symptoms, as triggers can be different for everyone.
If you regularly eat late and your meal often is takeout, consider if you can realistically plan your meal a little earlier on certain days of the week. A baked potato with whatever toppings you tolerate well, leftover chicken and rice, or a simple sandwich may be easier to manage on a weeknight than a large takeout meal after a long, tiring day.
Writing down what you eat during the day and when you have symptoms can help you remember what might be causing them during your doctor’s appointment instead of trying to remember what you ate and when over the course of a month.
Less Alcohol Still Matters Below Heavy Drinking
The National Cancer Institute states that even light drinkers can be at increased risk for certain cancers. Calling a drink casual or social doesn’t change what’s in your glass.
Make a decision about what you’re going to drink instead of alcohol. Having a go-to alcohol-free option stocked in your house can come in handy whether it’s a night of dining at home or a get-together with friends. Maybe it’s iced tea. Maybe it’s water. Something that sounds good to you, and it doesn’t have to be an expensive brand, is fine.
It’s much easier to follow through on specific, concrete habits. Deciding what you’re going to drink at dinner tonight is much easier than resolving to be healthy. When it’s 7 pm tomorrow night and it’s time to pour your drink, there’s nothing left up to interpretation.
A Probiotic Is Not an Automatic Next Step
Supplement aisles make it seem as though digestive tract wellness is an ailment easily remedied with a trip to the store for the right bottle. But a bottle of pills isn’t always that simple, or guaranteed to help.
According to the National Center for Complementary and Integrative Health, probiotics may have a variety of effects in the body, and different probiotics may act in different ways. Evidence of an organism’s effectiveness for a certain health issue doesn’t mean that another probiotic will help with your symptoms.
Before making your purchase, it’s good to know what issue you’re trying to deal with, because constipation, diarrhea, and reflux are all separate complaints. When in doubt, it’s better to talk with your clinician about scientific evidence for certain products and illnesses, rather than purchasing the bottle with the biggest numbers.
When Food Changes Are Not Enough
If your complaints continue, it’s okay to seek medical attention, as your diet doesn’t have to be perfect before you ask for help. It’s always better to visit a doctor and have your digestive troubles evaluated. Your physician may be able to determine a cause or issue that continued food elimination won’t fix.
Take a list of your symptoms along with a list of the medications and supplements you’re taking to your doctor’s appointment. According to the NIDDK, you should see a doctor if constipation continues despite self-treatment and if you have a family history of colon or rectal cancer.
See the shorter list below for the symptoms that mean seeing a doctor right away.
See a doctor right away if constipation comes with any of these:
- bleeding from your rectum
- blood in your stool
- constant pain in your abdomen
- inability to pass gas
- vomiting
- fever
- lower back pain
- losing weight without trying
The Worst Foods for Gut Health – In Conclusion
We always like to preach everything in moderation. But when it comes to gut health, it’s best to steer clear of fried foods, processed meats and excessive drinking. As much as you can, anyway. Sometimes it’s too hard to turn down that fried chicken. We get it. We love that stuff, too. But it’s always good to know what to cut back on to give yourself the healthiest gut you can.
Christine Morgan is a Registered and Licensed Dietitian who currently practices in dialysis. Her experience includes renal nutrition, food service, and geriatrics. Her education includes a Bachelor of Science in Nutrition and Dietetics from West Chester University of Pennsylvania, and she completed her Dietetic Internship with the University of Delaware. She is also a member of the Tri-State Renal Dietitians Association.
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