Food intolerances occur when the body is unable to digest or break down certain foods – often resulting in symptoms like bloating, diarrhoea, and nausea. According to the Food Standards Agency, food intolerances are incredibly common, with over 30% of UK adults having some type of adverse reaction.
Unlike some food allergies, which can be life-threatening, food intolerances aren’t usually dangerous to health. However, if left unchecked, they can significantly impact daily life.
For this reason, if you’ve been experiencing symptoms, identifying which foods you may be intolerant to can be helpful.
Here, we’ll look closer at eight of the most common food intolerances, including signs and ways to help manage your symptoms.
What are food intolerances and how do they differ from allergies?
According to the NHS, a food intolerance occurs when the body is unable to break down food and digest it properly. Symptoms vary depending on what you’re intolerant to, but can include anything from bloating and diarrhoea to hives and nausea. Food intolerances aren’t usually serious, but can make you feel unwell.
Symptoms can occur anywhere from a few hours to a few days after eating the food you’re sensitive to. How much you eat of it and which other foods you eat in the same meal can also impact the severity of your reaction.
While food intolerances and allergies are both reactions to food, they differ in the body response they trigger. Food allergies involve the immune system, leading to potentially life-threatening reactions like anaphylaxis, while food intolerances affect the digestive system and typically cause less severe symptoms.
You can read more about the difference between food allergies and intolerances on the Allergy UK website.
What causes food intolerances?
A food intolerance is the result of your body not being able to digest a certain food or ingredient in food properly. Experts are currently unsure exactly why food intolerances develop. However, research has identified several potential reasons.
In some cases, people may lack the enzymes (proteins) needed to break food down and digest it. For example, having low levels of the enzyme lactase makes it difficult to digest lactose, the sugar found in milk and other dairy products. Other times, food intolerances may be the result of sensitivity to certain chemicals found in food. Examples include histamine (found in wine, cheese, and processed meats) and salicylates (found in various fruits, vegetables, and spices).
Lastly, many experts believe that food intolerances are at least partly caused by poor gut health and changes to the gut microbiome, caused by illness, medications, or poor diet.
Certain health conditions, such as coeliac disease, ulcerative colitis, Crohn’s disease, and leaky gut, may also increase your risk of food intolerances. Leaky gut, for example, which occurs when the gut lining becomes damaged, can cause undigested food particles to enter the bloodstream – potentially triggering an immune response that leads to intolerance.
To learn more, you might like to read this comprehensive guide to the causes of food intolerances from Healthpath.
How are food intolerances diagnosed?
If you suspect you may have a food intolerance, it’s important to speak to your GP. If necessary, they may refer you to a food and nutrition specialist (dietitian) for tests.
Your dietician may recommend blood tests or a special diet where you avoid eating the food you may be intolerant to, to see if your symptoms improve. You may be asked to keep a food and symptoms diary to help identify triggers. Breath tests may also be used for suspected lactose intolerance.
It’s important not to cut our foods from your diet without the advice of a GP or dietitian. Elimination diets aren’t suitable for everyone and can increase the risk of vitamin and mineral deficiencies.
Note: There are various home tests available that claim to diagnose food intolerances. However, the NHS recommends avoiding these as there’s limited evidence of their accuracy, and they may encourage you to avoid multiple foods, which can be harmful.
8 of the most common food intolerances
You can be intolerant to almost any food. However, some food intolerances are more common than others. We’ll cover some of the most common food intolerances below.
1. Lactose
Lactose is a type of sugar found in milk and other dairy products. The body relies on lactase enzymes to digest lactose, and intolerance occurs when there’s a shortage of these.
Lactose intolerance is one of the most common food intolerances. Research estimates that 65% of the world’s population has trouble digesting lactose.
Common symptoms of lactose intolerance include abdominal pain, bloating, gas, diarrhoea, and nausea. Products high in lactose include milk, cheese, yoghurt, ice cream, and many baked goods. Aged cheeses and fermented dairy products, such as kefir, may be easier for people with lactose intolerance to tolerate because they contain less lactose than other dairy products.
2. Gluten
Gluten is a type of protein found in certain grains like wheat, barley, and rye.
Gluten intolerance, also known as non-coeliac gluten sensitivity, differs from coeliac disease, which is an autoimmune condition caused by an adverse reaction to gluten. People with gluten intolerance may experience similar symptoms to those caused by coeliac disease, such as gas, bloating, and abdominal pain, but without damage to the small intestine.
That said, both gluten intolerance and coeliac disease are managed by following a gluten-free diet. This involves avoiding gluten-rich foods, such as bread, pasta, beer, cereals, crackers, baked goods, and sauces – particularly soy sauce. Check out our article, 10 tasty gluten-free recipes, for inspiration.
3. Caffeine
Caffeine is a type of chemical found in various foods and drinks, including tea, coffee, chocolate, and energy drinks. As a stimulant, caffeine increases alertness by suppressing adenosine, a chemical that helps you sleep, and increasing adrenaline production, which boosts energy.
Most people can consume up to 400mg of caffeine (around four cups of coffee) per day without experiencing side effects. However, for those with caffeine sensitivity, the body’s response to these chemicals is heightened. You may experience symptoms like headaches, shakiness, heart palpitations, anxiety, irritability, diarrhoea, and other digestive issues, even after consuming very minimal amounts of caffeine.
Research suggests that caffeine intolerance may be caused by genetics, as well as a reduced ability to break down and remove it from the body.
4. FODMAPs
FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. These are short-chain carbohydrates that occur naturally in certain foods.
FODMAPs are difficult for the body to digest and are a common cause of digestive issues. Instead of being broken down by friendly gut bacteria in the small intestine and absorbed into the bloodstream, FODMAPs reach the colon, where they’re fermented by bacteria, causing gas, bloating, and abdominal discomfort.
High-FODMAP foods include mango, cauliflower, beans, onions, and fruit juices. For further reading, check out our article: The low-FODMAP diet – what is it and what are the benefits?
5. Salicylates
Salicylates are natural compounds found in certain fruits, vegetables, and spices, like prunes, cumin, and broccoli, as well as products and medications like toothpaste and aspirin.
Salicylate intolerance is less common than gluten or lactose intolerance. However, it’s a real issue for some people and can cause symptoms like sinus infections, blocked nose, diarrhoea, hives, and gut inflammation.
Research suggests that salicylate sensitivity may be caused by an overproduction of leukotrienes – molecules that help to regulate the body’s inflammatory response. Studies have also found that salicylate intolerance is more common in people with asthma, food allergies, and inflammatory bowel disease.
6. Fructose
Fructose is a type of sugar found in fruit and vegetables, as well as sweeteners like honey, agave, and high-fructose corn syrup. It’s also a type of FODMAP.
General consumption of fructose has increased significantly over the past four decades (particularly from sugar-sweetened drinks), which research has linked with a higher risk of conditions like obesity, liver disease, and heart disease.
Experts have also noted an increase in fructose malabsorption and intolerance. When the body can’t absorb fructose properly, it travels to the large intestine, where it’s fermented by gut bacteria, resulting in digestive issues like gas, reflux, nausea, and diarrhoea.
High-fructose foods include honey, apples, agave nectar, cherries, pears, watermelon, sugar snap peas, and foods containing high-fructose corn syrup.
Many people who are intolerant to fructose tend to be sensitive to other FODMAPs, and may benefit from the low-FODMAP diet.
7. Amines
Amines are organic compounds found in various foods and produced naturally by the body. There are various types, but histamine is most commonly associated with food-related intolerances.
Histamine plays a role in the digestive, immune, and nervous systems – helping to protect the body against infection. It does so by triggering immediate inflammatory responses, such as sneezing, itching, and watery eyes, to rid the body of potentially harmful molecules.
People with histamine intolerance are unable to break histamine down properly, causing it to build up in the body. This can result in symptoms like headaches, skin flushes, hives, itching, anxiety, and stomach cramps.
Foods high in histamine include cured meats, dried fruit, citrus fruits, avocados, smoked fish, vinegar, and fermented foods.
8. Sulfites
Sulfites are chemicals mainly used as preservatives in certain foods, drinks, and medications. For example, sulfites are added to dried fruit to slow browning and to wine to prevent spoilage caused by bacteria. They also occur naturally in foods like grapes and aged cheeses.
Common symptoms of sulfite intolerance include hives, skin swelling, blocked nose, flushing, diarrhoea, and wheezing. Anyone can develop an intolerance to sulfites, but research has found that it’s most common in people with asthma. In some cases, sulfites can cause airway obstruction in asthmatic patients with sulfite sensitivity, which can be potentially life-threatening.
Other sulfite-containing foods include apple cider, canned vegetables, condiments, pickled foods, tea, beer, and baked goods.
Final thoughts…
While rarely life-threatening, food intolerances can be frustrating to manage and impact daily life. However, the good news is that, with a bit of trial and error, most people can identify which foods they’re intolerant to and take the steps necessary to reduce symptoms.
For further reading, head over to our gut health section. Here, you’ll find information on everything from the gut-brain connection to the role of probiotics and prebiotics in gut health.
Are you intolerant to any foods? Do you have any experience or tips that you’d like to share? We’d be interested to hear from you in the comments below.
