What Causes Food Intolerances?
Nobody really knows for sure what causes food intolerances. Research is beginning to help us uncover some of the likely ...
Nobody can tell you which foods will trigger your IBS symptoms.
Because IBS has many causes, everyone with IBS will have a different set of trigger foods. Some people with IBS have no trigger foods at all: hormones, stress, or medication could trigger their symptoms instead.
An almost infinite number of factors are involved in Irritable Bowel Syndrome (IBS). It’s impossible to list them all here.
It’s important to remember that IBS is a collection of symptoms: it isn’t a disease, it’s a label.
A disease has a known cause that produces a known pathophysiology (changes in the normal function of your cells) that results in damage to your body. Your symptoms then happen as a result of that damage.
Nobody has ever found one cause for IBS, and they never will, because IBS is a diagnosis of exclusion: it’s a label you get once ‘serious’ diseases have been excluded.
If you have IBS, you’ve probably had tests for a few possible conditions like Inflammatory Bowel Disease (IBD) or coeliac disease. If you don’t have anything serious wrong with you, you might get told you have IBS.
To have IBS, you have to meet something called the “Rome III diagnostic criteria”: recurrent abdominal pain or discomfort at least three days per month for the last three months, with your symptoms having started six months ago.
You can find out more about how you get a diagnosis of IBS in our blog What are the warning signs of IBS?
You need to meet two or more of the following criteria:
But what if you only experience symptoms once a month, but they last for a week? On that basis, you wouldn’t have IBS, but this pattern is actually quite common in women, in the week before their period or during their period.
Our goal at Healthpath is to treat the cause, not just suppress symptoms. The problem with a diagnosis of IBS is that it distracts from the real problem and doesn’t lead us towards a real solution.
To learn more about IBS symptoms, check out our conditions page.
There is no one diet that’s best for IBS.
There are many diets that can reduce IBS symptoms, but a diet that works well for one person with IBS could be a disaster for someone else with the same symptoms.
Read on to explore some of the diets that have good evidence behind them for reducing IBS symptoms.
FODMAP is an acronym that represents types of carbohydrates that have been found to increase IBS symptoms: mostly diarrhoea and bloating.
The ‘F’ stands for ‘fermentable’, meaning that our gut microbes like to eat them.
‘O’ stands for oligosaccharides
‘D’ stands for disaccharides
‘M’ stands for monosaccharides
‘A’ stands for ‘and’
‘P’ stands for polyols
Find out all you need to know about the low-FODMAP diet in our blog NHS FODMAP diet: the complete guide.
The SCD works in a similar way to the low-FODMAP diet: it restricts the carbohydrates that microbes like to eat.
However, it restricts different ones, so it’s actually quite different to the low-FODMAP diet.
The SCD only allows foods that have no—or very low levels of—disaccharides or polysaccharides. In reality, that cuts out grains and starches, and most dairy products too.
That leaves you with meat, fish, eggs, vegetables, fruits and nuts, which are the most nutrient-dense foods. That makes the SCD a very healthy diet to follow,
The SCD has been proven to be very effective at reducing the symptoms of:
The Autoimmune Protocol is a restrictive diet that eliminates many foods temporarily. The aim is to reintroduce foods gradually after a period of around six weeks.
Similar to the SCD in that grains, dairy and processed foods are out, it also excludes nuts, nightshades (tomatoes, peppers and aubergines) and eggs. This is because research and experience has shown that they’re the foods you’re most likely to be allergic or intolerant to.
The AIP is a useful tool for reducing the symptoms of many autoimmune diseases. There’s even evidence that it’s put some people with autoimmunity into remission: although autoimmunity can’t be cured, the symptoms can sometimes disappear.
The list of foods you should avoid for your IBS symptoms is individual to you.
While it would be fantastic to have one, definitive list that works for everyone with IBS—or even most of them—sadly no such thing exists. There are certainly foods that you’re more likely to react to, which is why the diets above exist, but there are plenty of people who don’t respond to these diets at all.
Some people even find that starchy, processed foods are the only ones that keep their symptoms away. Others find that a low-FODMAP diet makes their symptoms worse: in fact, people with constipation rather than diarrhoea sometimes need to eat FODMAPs to keep their gut moving.
However, if you have IBS symptoms, check out the list below for the foods that are most likely to bother you.
Also, read our blog: What are the best foods for leaky gut?
Sugar is rocket fuel for most microbes.
That means that if your microbiome is imbalanced (if you have IBS this is almost certainly the case), feeding your microbes sugar is likely to make it worse. There’s evidence that our less ‘friendly’ microbes like sugar a lot more than our friendly ones.8
Bad news: all types of sugar, no matter how natural they are, will turbo-charge dysbiosis (an imbalance of the bacteria and other microbes in your gut). That goes for honey, maple syrup, rice syrup, coconut sugar or anything else that’s marketed as a healthy alternative to sugar.
Some of them are better—generally speaking—than others, but if you want to work on your microbiome, we don’t recommend any of them, except as an occasional treat. If you want something sweet, go for nature’s candy: fresh fruit.
The evidence that gluten is problematic for many people is now too overwhelming to ignore.9
While people with no IBS symptoms—who have healthy guts with robust microbiomes and strong immune systems—could tolerate gluten with no problems, if you have a health condition, we recommend you avoid it.
While many people with IBS symptoms benefit from a grain-free, paleo style diet with lots of meat, fish, eggs and vegetables, others feel better when they eat whole grains like brown rice or quinoa. Stay away from processed gluten-free foods like cakes and biscuits: they’re just as nutrient-free as the regular ones!
It’s true: dairy does contain high levels of calcium, protein and b vitamins, all essential for good health. Unfortunately, for many people, milk products are too hard to digest.10
Ever heard the saying ‘you are what you eat’? We prefer ‘you are what you eat and absorb.’ Not so catchy, but if you have trouble digesting and absorbing the nutrients in some foods, they’re not doing you much good.
Most of the world has a problem with dairy. People with European heritage are usually ok, because their ancestors were dairy herders and farmers: they evolved with dairy in their diet. But some ethnicities have no history of consuming dairy: only 8% of people in China, for instance, are dairy-tolerant.11
There is no requirement for a white liquid in your diet, but because so many of us have grown up with milk, we like it!
We don’t usually recommend soya as a lot of people are intolerant to that too, so go for a coconut, almond or rice milk with no additives, gums or thickeners. They can be hard to find in the shops, so try making your own! It’s easy and there are plenty of recipes online.
A lot of people with IBS are told to avoid fatty foods, but most people find they can tolerate some fats, like the ones found in whole foods like nuts, avocados and oily fish.
If you feel ill after a greasy takeaway, it’s more likely that you’re intolerant to the highly-processed, potentially toxic fats that restaurants use. These ‘industrial’ fats go through chemical and super-high heat processing to extract the maximum amount of oil out of the seeds. The result is a highly-inflammatory, unnatural product that has been shown to be bad for our health.12
Oils should be extracted naturally: by hand, or manual machine. Look for words like ‘cold-pressed’ or ‘extra virgin’ on the label. Avoid refined oils that you get in big containers.
Beans and legumes are chock-full of fibre, vitamins and protein, but unfortunately they also come with a hefty dose of FODMAPs, lectins and phytates (plant chemicals that can irritate your gut and prevent you from absorbing nutrients).
The good news is you can minimise lectins and phytates by soaking your beans and legumes.13 The bad news is that soaking won’t reduce FODMAPs, or their wind-making potential.
Depending on the dish, chopped vegetables like pepper, courgette, aubergine, carrot or squash can replace beans. You still get a great array of nutrients and fibre, but no uncomfortable after-effects.
Nobody would deny that most shop-bought cakes, biscuits, crisps, puddings and pastries are delicious. But did you know that the companies that make those products spend a lot of money on paying clever people to find out exactly how to get us hooked on them?
We’re quite literally designed to find and eat the foods that give us the most calories in the smallest package. That’s what kept us alive over 200,000 years living outside. It’s no coincidence that the foods we can’t stay away from are the worst for us.14
The closest thing to junk food for a caveman was a nut: not much danger of overeating hazelnuts if you have to pick them all yourself. The problem today is that our environment and the foods we eat are totally out of sync with our bodies and genes, which haven’t changed since paleolithic times.
When you make your own food from scratch, you know exactly what’s in it. Ever made a cake and seen how much sugar goes into it?
Today, there are a lot of healthy, alternative ingredients in supermarkets. Almond flour, coconut flour and an array of natural sweeteners (which you should use sparingly) are easy to find, and there are an infinite number of recipes online. Make a carrot cake with coconut flour, a little honey and fresh carrots and you’ll never get one from the supermarket again.
Diet drinks might seem like a harmless sweet treat but the evidence is stacking up that they could be even more harmful than their full-sugar relatives.
There are many different types of sugar-free sweeteners on the market now, and while some fall into the ‘probably ok in small amounts’ category, others are probably best completely avoided. The problem with all artificial sweeteners is that they ‘trick’ your tastebuds into ‘thinking’ that sugar is on its way, and your body prepares accordingly.15
Studies have shown that diet drinks increase the risk of diabetes by negatively affecting gut bacteria, insulin levels, and insulin sensitivity. They also cause blood sugar levels to spike16 and make you more likely to gain weight around your waist than consuming non-sweetened, plain drinks.17
Blood sugar swings can cause IBS symptoms in some people, but that’s not the only reason to avoid artificial sweeteners if you’re looking after your gut health. The sweeteners themselves can also alter the movement of your gut, causing either constipation or diarrhoea.18
Sadly, no healthy sweet beverage exists. That doesn’t mean you can’t have a can of Diet Coke occasionally: just save fizzy drinks for special occasions.
If you crave a cold, sweet bubbly drink, try fizzy water with a splash of fruit juice, or just a squeeze of lemon or lime.
For some people with IBS, chocolate is the perfect storm of symptom-inducing ingredients: sugar, milk and cocoa.
We’ve covered sugar and dairy already, so what’s the problem with cocoa? The answer is nothing, neccessarily. It’s actually a powerful polyphenol (plant chemical) which can boost gut health by encouraging friendly bacteria to grow.
But cocoa is a legume, which is a problem for some people, and it’s also high in histamine, a chemical compound that can cause issues in your gut and beyond, if you’re sensitive to it.19
Sometimes you just need a sugar hit, and only chocolate will do. Depending on which element of chocolate brings on your gut symptoms (the dairy, the sugar or the cocoa, or all three), try these instead:
If you’re used to having a glass of wine or a beer to relax, cutting down on alcohol can feel like a punishment. While you don’t need to cut it out completely, studies have shown time and time again that excessive drinking sets you on a path to ill-health.
As far as your gut is concerned, alcohol promotes gut inflammation, which disturbs the delicate immune system there. It also encourages less-friendly bacteria to grow and proliferate, causing dysbiosis and leaky gut.20
However, if you’re a fan of red wine, lucky you! A 2020 study confirmed that a moderate amount of red wine actually diversifies your microbiome, leading to a whole host of health benefits.21
You don’t need to ban alcohol from your life, just reduce it to a sensible amount. A useful guideline is the 1-2-3 rule (one drink a day, no more than two at once, no more than three times a week).
Try to minimise sugary mixers too. Some of the lowest sugar drinks include:
Both of these ‘allium’ vegetables are well known for their ability to cause IBS symptoms like bloating and diarrhoea. This is because they’re both high in fructans, a type of FODMAP.
In a healthy gut, fructans don’t cause uncomfortable symptoms. They’re prebiotics that feed bacteria, both good and bad. In an imbalanced gut, they add fuel to the fire.
It’s hard to replace the rich, savoury flavour that garlic and onions bring to meals, but try:
Identifying food triggers for your IBS symptoms can be the easy part. If you don’t mind using some dietary restrictions to figure out what’s causing your digestive issues—like diarrhoea, constipation or bloating—you can discover which foods you need to avoid in as little as a week. You may only need to avoid dairy, or gluten, for example.
If you have lots of food intolerances however, the process will take longer and you might need the help of a professional, like a Registered Nutritional Therapist.
Alexandra Falconer MA (Dist) DipCNM mBANT is a Registered Nutritional Therapist specialising in IBS and related conditions. A graduate of Brighton’s College of Naturopathic Medicine, she is committed to fighting the root causes of chronic illness and bringing functional medicine to everyone who needs it.
Before her natural health career, Alex was a journalist and copywriter. She continues to write for magazines and media agencies, and now combines her two great passions—writing and health—by creating content that empowers people to claim their right to a healthy body and mind.
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