Nature's Insights

Intolerance to foods - What is a food intolerance and the most common ones

What is a food intolerance?

Food intolerance refers to difficulty in digesting certain foods, this differs from a food allergy which involves the immune system and not the digestive system. Food intolerances are not life-threatening whereas food allergies can be fatal. 

In a healthy body, when food is eaten it is broken down by enzymes digest that makes it small enough to pass through the small intestines and into the blood. However, if the specific enzyme is not available, the proteins and sugars in the food cannot be broken down and cause some nasty effects to our bodies.

What are the symptoms?

Symptoms of a food intolerance usually start within a few hours of eating the food you are intolerant to, however, symptoms can be delayed. Common symptoms include diarrhoea, bloating, rashes, headaches, nausea, fatigue, abdominal pain, runny nose, reflux and flushing of the skin.

How can food intolerances be diagnosed?

Food intolerances can be and are commonly diagnosed by elimination diets which remove the most commonly associated foods for a period of time until symptoms subside. The foods are then reintroduced and monitored for symptoms.

Most common food intolerances in the UK


Dairy products such as milk contain a sugar called lactose. Lactose is broken down by lactase enzymes and they are required for lactose to be properly digested and absorbed. When there is a shortage of lactase enzymes, this causes lactose intolerance. Symptoms include; abdominal pain, bloating, diarrhoea, gas, and nausea.


Gluten is a protein found in wheat, barley, rye and triticale. There are a few conditions related to gluten intolerances, the most well-known being coeliac disease which involves the immune system attacking the small intestine and causing serious harm to the digestive system. Symptoms include bloating, abdominal pain, diarrhoea or constipation, headaches, fatigue, joint pain, skin rash, depression or anxiety and anaemia. This can be managed with a gluten-free diet and eating alternatives such as gluten-free bread.


Caffeine is a chemical and a stimulant (increases alertness and decreases fatigue) that is found in most beverages, including coffee, fizzy drinks, tea and energy drinks. If someone has difficulty consuming caffeine they may suffer from the following symptoms: rapid heartbeat, anxiety, jitters, insomnia, nervousness, restlessness.


Fructose is a sugar found in fruits and vegetables and sweeteners such as honey. In people with a fructose intolerance, fructose isn’t efficiently absorbed into the blood and instead remains in the intestines. Here it is fermented by gut bacteria which produce hydrogen, carbon dioxide and methane in the gut, and cause digestive problems such as reflux, gas, diarrhoea, nausea, abdominal pain, vomiting and bloating.


If you have an intolerance to nuts, your body produces an inflammatory response to one or more of the nut proteins. Be aware that a nut intolerance is different to a nut allergy, if you have an allergy, you may feel unwell immediately after consuming nuts, however, if you have an intolerance the reaction may be delayed and less severe. Symptoms may include stomach pain or cramps, flatulence, nausea, vomiting, diarrhoea.



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