Food Intolerance Definition, Symptoms, Diet, Treatment

Although foods are important for sustaining life, sometimes it can be a problem and trigger a reaction. This may occur for different reasons and with various conditions. It can occur almost immediately after consuming the food or within minutes or even hours thereafter. Food intolerances are one type of reaction to eating specific foods and may affect only certain people.

Meaning of Food Intolerance

Food intolerance is a non-immune response to eating certain foods usually due to an inability to digest the specific food. One of the most commonly known food intolerances is lactose intolerance which is an intolerance to dairy. It can cause a host of symptoms, particularly digestive symptoms like nausea, bloating and diarrhea. This lasts for a few hours or even for a day or two but does not usually lead to any serious complications. In other words, a food intolerance is not life-threatening but can affect a person’s life in terms of their dietary choices.

Food Intolerance vs Food Allergy

It is important to stress that the response or reaction in a food intolerance is not related to the immune system. With a food allergy however, there is an immune response to the presence of certain foods in the gut. Here the immune system is hypersensitive and incorrectly reacts to these foods as it would to an invading threat. Therefore a food intolerance is also referred to as a non-allergic or non-IgE mediated food hypersenstivity.

Causes of Food Intolerance

Despite the strong stomach acid and powerful digestive enzymes that are secreted into the human gut, it is not able to digest every substance within food in order to absorb it. For example, fiber is indigestible but still plays an important role for digestive health within the gut until it is passed out with stool. This is not considered as a food intolerance. However, when certain foods that are digestible for most people cannot be digested by others or suddenly becomes indigestible then it is considered to be a food intolerance.

Lack of Enzymes

Digestive enzymes are specific for certain types of foods. If there is a lack of a certain digestive enzyme then a specific food may not be digested in the gut. This is one of the main causes of food intolerance and the reason for lactose intolerance. In this intolerance to dairy products, there is a deficiency of the enzyme known as lactase. It is needed to digest the milk sugar known as lactose which is present in dairy.

Substances in Foods

Sometimes the constituents of a specific food may irritate the digestive tract for various reasons or remain in the gut undigested despite the presence of digestive enzymes. It may vary with individual tolerance to these foods and is more likely to occur with certain foods. This may be seen with the following foods and substances:

  • Caffeine in coffee, tea, chocolates.
  • Amines in cheese.
  • Toxins in foods like aflatoxins (fungal) or bacterial toxins.
  • Histamine found in decomposing fish.
  • Salicylates found in most fruits, vegetables and herbs.
  • Additives including colorants, flavorants and preservatives, such as nitrates and MSG.


There are certain diseases where the ability to digest foods are impaired or certain foods tend to trigger digestive symptoms. This is seen in:

  • Irritable bowel syndrome (IBS) where certain foods trigger or aggravate symptoms.
  • Pancreatic exocrine insufficiency where the secretion of digestive enzymes from the pancreas is impaired.
  • Gallbladder disease where a lack of bile affects the emulsification and digestion of fats.

Although thesee reactions to foods are not actually a food intolerance, it may nevertheless cause similar symptoms and should be considered as a possible cause.

Symptoms of Food Intolerance

It is important to understand why the symptoms of a food intolerance may arise. The presence of undigested nutrients may have a host of effects even though these foods are harmless, as is seen with lactose in dairy and gluten in wheat. These substances can draw out water from the body into the gut by changing the osmotic gradient. It can also serve as additional nutrition for naturally-occurring microbes in the bowel thereby leading to an overgrowth.

With other substances, such as toxins and histamine, it may trigger inflammation of the gut. This can also cause water to pass out into the gut but also impair the digestion of other nutrients. Furthemore inflammation leads to symptoms like pain. Despite different reasons for these food intolerances, the common symptoms that tend to occur includes:

  • Bloating
  • Nausea and sometimes vomiting
  • Diarrhea
  • Stomach ache
  • Abdominal cramps
  • Excessive gas
  • Heartburn

Non-digestive symptoms like headaches and irritability may also arise with a food intolerance. Other symptoms like shortness of breath, itchy skin and so on may be more likely to occur with a food allergy rather than a food intolerance.

Read more on food allergy and food intolerance tests.

Diet for Food Intolerance

It is important to first identify the exact food or group of foods that are the problem. This can be done with a food diary and an elimination diet. Once the trigger food(s) are identified, then it should be avoided as far as possible. This is the main dietary approach to managing a food intolerance.

However, a food intolerance may not be a lifelong phenomenon. Eventually a person can develop a tolerance to the trigger food and this should be tested for occasionally. If the symptoms do not return after eating a small amount of the previously identified trigger food, it may be a sign of tolerance that has now developed.

Read more on foods to avoid for lactose intolerance.

Treatment of a Food Intolerance

Sincea food intolerance is not a serious condition in most instances, it can be conservatively managed by avoiding the trigger food. Most people with a food intolerance will have one or just a few trigger foods. Avoiding these foods will not usually lead to any nutritional deficiencies.

Enzyme supplements may be available which can help with management. By using these supplements, the deficient enzyme can now be replaced. Small quantities of the trigger food can then be consumed with little or no symptoms. However, this may not be a solution for all types of food intolerance.

Usually the symptoms of a food intolerance resolve after a few hours or a day or two at most. If they symptoms are severe, certain medication can be temporarily used for symptomatic relief. This includes anti-emetics to stop vomiting, antidiarrheal agents to stop diarrhea and anti-spasmodic agents to reduce abdominal cramps. These drugs should only be used after consulting with a medical professional.

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