Woman with arms up to gesture weighing options. Allergens hover above left hand, a stomach hovers above the right hand. She gazes at the stomach with curiosity.

Food Allergy vs. Food Intolerance: Which Is It?

As someone living with IBS, you know that the management is aimed at controlling symptoms through diet and lifestyle. IBS symptoms are often attributed to adverse food reactions.1 Research has suggested that 84 percent of people with IBS report food-related symptoms.2 You may feel that your body reacts negatively when you eat a particular food, and your symptoms flare. Are you wondering if the cause of such flare-ups is an allergy or food intolerance? Here is what you need to know!

Food allergies

Due to similarities in symptoms when certain foods are eaten, food allergy and food intolerance are often confused. Food allergy involves an immune response, more specifically, the activation of IgE antibodies to fight the protein in the food that you just consumed.3 A food allergy usually starts within minutes to one hour of consuming the food and can affect the skin, respiratory tract, and gastrointestinal tract.3

It is important to note that symptoms can first appear several hours after the food was eaten. Although some of these symptoms, especially the cramping, diarrhea, and abdominal pain, do occur in people with IBS, there is little evidence of a relationship between IBS symptoms and an IgE-mediated food allergy response.3 Less than three percent of adult cases with IBS have food allergies, so symptoms are more often than not a food intolerance.4 Other food allergy symptoms include skin rash, itching, hives, swelling of the tongue or throat, or difficulty breathing. Symptoms can range from mild to severe.

Food intolerances

In contrast to food allergies, food intolerances do not activate an immune response and do not produce antibodies. With food allergies, a little bit of the food can have a significant reaction, whereas food intolerances are more dose-dependent. Some of the symptoms of food intolerance can be similar to those of a food allergy, with the exception of shortness of breath or anaphylaxis. With my clients, I often see headaches, irritability, or heartburn with food intolerances. Food intolerances tend to take longer to appear and are mainly triggered by the digestive tract.

Symptoms due to food intolerance are often a result of food components not being digested or absorbed well.5 When food is not digested or absorbed well, the gut produces extra gas, or excess water is drawn into the bowel.5 These effects cause the typical IBS symptoms- abdominal pain, bloating, diarrhea, or constipation.5 One study revealed that more than 50 percent of IBS subjects reported food intolerances, a rate that was double the amount indicated by non-IBS subjects.6

Common food intolerances in people with IBS

Short-chain carbohydrates: there are several groups of short-chain carbohydrates that are known as FODMAPs. FODMAP stands for fermentable oligosaccharides, disaccharides, and polyols. They are fermented quickly in the gut and can be poorly absorbed. Most people with IBS are intolerant of at least one of these groups of FODMAPs and are unable to absorb them:7

  • Oligosaccharides (fructans and galacto-oligosaccharides [GOS]): wheat, rye, onions, garlic, legumes.
  • Lactose: dairy products (milk, cheese, yogurt). Many people with lactose intolerance can enjoy dairy spread out throughout the day.
  • Fructose (especially in excess of glucose): fruits, honey, high fructose corn syrups.
  • Polyols (sorbitol and mannitol): naturally occurring sugars found in some fruits and vegetables and used as an artificial sweetener.

To see a full list see the Low FODMAP Diet.

Pharmacologic agents (i.e, histamines, sulfites, caffeine)

All of these cause different reactions and symptoms. Caffeine intake should be considered on a case by case basis. In general, daily intake should be restricted to 400 mg caffeine, a safe limit for most people. Sources of caffeine not only include coffee, but also tea, energy drinks, soda, and even dark chocolate!15

Enzyme deficiency

This means lacking the enzymes that break down sugars. As a result, the sugars sit in the intestines and is broken down by gut bacteria, causing gas, pain, and bloating.8

Host-specific metabolic disorders (ie, alcohol intolerance)

Such disorders can irritate the gut and exacerbate symptoms like cramping and bloating. In a recent study of 330 adult subjects with IBS, one-third of the subjects complained that alcohol initiated their IBS symptoms. In general, alcohol can impact intestinal motility and absorption and many alcoholic beverages contain FODMAPs.14 In about a third of my clients, I’ve seen good after decreasing or cutting out alcohol.

Reactions to food additives or preservatives


This substance is considered a low-FODMAP item and is better absorbed compared to other sugar alcohols. However, recent studies have proven that it may interfere with fructose absorption, causing discomfort in the abdominal area.13

Sugar polyols (i.e, lactitol, xylitol, isomalt, maltitol)

These are also high in FODMAP, as noted above, and can lead to symptoms because they cause excess water to be drawn into the gut resulting in diarrhea. They are also poorly absorbed in the small intestine, resulting in excess gas production.12

Spicy food

Many people with IBS report that the intake of spicy food often results in abdominal pain and gastroesophageal reflux. A recent study in Iranian adults suggested that eating spicy food at least ten times a week greatly impacted IBS symptoms in women. 15 Capsaicin, the active ingredient in red chili, can trigger abdominal pain and a burning sensation in IBS patients.15 However, it should be known that studies reporting such data have used high doses of spices.15

Closing thoughts

As you can see, there are key differences between food allergies and food intolerances. Once you rule out any food allergies, it’s important to take a closer look at foods that are the potential causes of your discomfort. If you suspect that one or more of the groups of FODMAPs is triggering your symptoms, a Registered Dietitian who specializes in IBS can guide you through the right approach to identifying those foods. This will help you manage your symptoms in the long run with a reduced-stress and strategic approach.

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