People toss around words like food sensitivities, food intolerances, and food allergies. Unfortunately, there’s not much accuracy to how they’re used in the public sphere. But all three represent real conditions that affect a lot of people. Sometimes our bodies don’t respond well to certain foods.

If you’ve been struggling with symptoms you can’t seem to address, it’s time to look at your food.

You may know that a food intolerance can cause uncomfortable digestive symptoms (like gas and diarrhea). Lactose intolerance is fairly common and has made the concept familiar. But food sensitivities involve an immune response that may show up in less expected ways, such as fatigue or headaches.

What is a food sensitivity?

A food sensitivity (also called food IgG hyperreactivity or hypersensitivity) occurs when the body’s immune system produces antibodies to a food. The specific type of antibody involved in food sensitivities is called an IgG antibody. It has a delayed response time, making food sensitivities sometimes hard to pinpoint. Your food sensitivity symptoms could occur an hour, a day, or even 48 hours later.

Food sensitivities, food intolerances, and food allergies

Food sensitivity vs. food allergy

A food sensitivity is not the same as a food allergy. A food allergy is an immune response involving IgE antibodies. This antibody causes immediate symptoms, such as:

  • Hives
  • Itching
  • Digestive distress
  • A swollen airway, also known as anaphylaxis 

Anaphylaxis is a life-threatening emergency. If you have a food allergy, it is not safe for you to consume the allergen in any amount.

While a food sensitivity is also an immune response, it involves different antibodies (IgG antibodies) than allergy. These antibodies are present in all people toward a broad range of foods and do not trigger allergic reactions. However, sometimes your body overproduces them toward a certain food. It is not life-threatening, and the symptoms generally are not immediate.

Food sensitivity vs. food intolerance

While people throw around the terms “food sensitivity” and “food intolerance” interchangeably, they are also not the same thing. A food intolerance means your body is unable to digest a certain food. For example, if you have lactose intolerance, you are unable to digest lactose (the sugar in cow’s milk), because you’re missing an important enzyme called lactase. A food intolerance causes digestive symptoms, not generalized symptoms.

In a food sensitivity, your digestive system is not the problem. You can digest the food, but your immune system overproduces IgG antibodies to it. This triggers an immune system reaction that can cause symptoms in the digestive tract and throughout your body. 

Comparing all three: food sensitivity, food intolerance, and food allergy

  Allergy Sensitivity Intolerance
Cause IgE antibodies IgG antibodies Inability to digest certain food (structural problems or lack of enzymes)
Symptoms Immediate problems swallowing or breathing, vomiting, itching, hives. Possibility of anaphylactic shock. Delayed and varied symptoms: digestive problems, fatigue, brain fog, sinus congestion, headaches, joint pain, sleep and mood changes, acne, and skin rashes. Relatively short delay. Digestive symptoms: gas, bloating, diarrhea or constipation, vomiting, and abdominal pain.

A note on gluten: celiac disease, wheat allergies, and gluten sensitivities

Gluten gets a lot of attention right now, with gluten-free products advertised in nearly every aisle of the grocery store. There are clearly a lot of people avoiding gluten.

Gluten is a protein that occurs naturally in some grains, like wheat, rye, and barley. However, it’s also added to many other products, from toothpaste to skin products.

So what’s the big deal with gluten?

Celiac disease

Some people have a condition called celiac disease. It’s a serious autoimmune disorder. When they eat gluten, their body’s immune system attacks and damages their small intestines. Some people with celiac disease experience significant gastrointestinal symptoms, while others don’t. Fatigue, joint pain, and even a general irritableness are all also common symptoms.

In fact, some people have what is commonly called “silent celiac disease,” or asymptomatic celiac disease. That is to say, even though antibodies are attacking and damaging their small intestines every time they eat gluten, they experience no symptoms. They’re still at-risk for long-term complications from celiac disease, and either a blood test or intestinal biopsy will be positive for celiac disease.

For some, the only reason they discover celiac disease is because a family member has celiac disease, and they decide to get tested too “just in case.” This is important, since you can cause irreversible intestinal damage by eating gluten when you have celiac disease.

I recommend always testing for celiac disease when a person thinks they may have a reaction to gluten, has any of the signs of celiac disease, or has a family history of celiac disease. Importantly, we always test before starting a gluten-free diet. It’s much easier to test when there’s still gluten in your system.

If you have celiac disease, regardless of how serious the symptoms feel, no amount of gluten is safe for your intestines.

Wheat allergy

A wheat allergy is a food allergy. Like with other food allergies, symptoms occur immediately or within minutes of eating wheat products. Symptoms include nausea, hives, difficulty focusing, and breathing problems. Food allergies, including wheat allergies, can lead to a life-threatening condition called anaphylaxis. 

If you have a wheat allergy, no amount of wheat is safe for you.

Gluten sensitivity

A gluten sensitivity is not the same as celiac disease or a wheat allergy, nor does it typically require the same level of vigilance. A gluten sensitivity can also be called non-celiac wheat sensitivity (NCWS) or non-celiac gluten sensitivity (NCGS). 

The biological mechanism of a gluten sensitivity remains unclear. It does not involve an autoimmune reaction (as in the case of celiac disease) or IgE antibodies (as in the case of a wheat allergy). But, up to 50% of individuals with non-celiac gluten sensitivity present with elevated IgG antibodies for gluten.

The symptoms of a person with a gluten sensitivity will vary. Some will have primarily gastrointestinal symptoms. Others may have headaches, skin conditions, joint pain, fatigue, or brain fog.

How much gluten a person with a gluten sensitivity can tolerate will vary. If you have a gluten sensitivity, you can largely gauge your dietary choices based on symptoms. While your body reacts to gluten, it is not life-threatening, nor does it cause lasting permanent damage.

How to test for food sensitivities and intolerances

The elimination diet

If you looked at the list of food sensitivity symptoms and couldn’t find a common denominator, you’re not alone. Researchers have found connections between IgG hyperreactivity and major depressive disordermigraines, and irritable bowel syndrome. The diversity of symptoms makes diagnosing a food sensitivity challenging.

If you have symptoms that seem to be worse after certain meals, or come and go, then it’s worth exploring.    

The most reliable way to test for food sensitivities is to follow an elimination diet. In an elimination diet, you remove all potential food triggers for a certain amount of time. Then you slowly add one food back in at a time, in a systematic fashion. The goal is to see which foods you react to and exactly which symptoms they’re causing.

Elimination diets are not easy to do on your own. You need knowledge and guidance for which foods to cut out and how to gradually reintroduce them. Moreover, it’s hard to cut out a long list of potential food triggers. You’ll need to figure what you can eat and how to get adequate nutrition during the elimination diet.

That’s why I don’t recommend patients do this alone. You want someone who can guide you every step of the way. They’ll help you figure out what to avoid and for how long. They’ll also provide guidance on what to eat during the elimination diet. The most important and challenging part is the reintroduction of foods. A skilled practitioner can guide you through this process.

Food sensitivity test

In certain cases, it can be helpful to complete a food sensitivity test. It will measure your levels of IgG antibodies for up to 80-90 different foods. Along with your symptoms and history, testing provides more information to be able to individualize your elimination and reintroduction diet. You will still need to follow an elimination diet, but it can help guide the process.

It’s important to have your lab results interpreted by a knowledgeable healthcare provider. Sometimes your IgG antibodies levels will suggest intestinal hyperpermeability, or “leaky gut syndrome.” This is when there is damage in the lining of the digestive tract. A leaky gut might occur with chronic stress, poor diet, drugs, alcohol, or infections.

Lactose intolerance

Among food intolerances, few have reliable tests. Practitioners may use a hydrogen breath test, if they are uncertain of lactose intolerance. Most of the time, doctors will diagnose lactose intolerance based on your symptoms, though. Most other food intolerances do not have an available test.

Allergy tests

Sometimes your symptoms of an intolerance or sensitivity will warrant further investigation. Your doctor may want to rule out that you do not have a food allergy. There are both skin tests and blood tests available to test for food allergens. If you do have a food allergen, you will need to drop the problematic food entirely from your diet.

Celiac disease testing

If you show signs of a poor reaction to gluten, your doctor may want to rule out celiac disease. If you have celiac disease, your immune system attacks the small intestines every time you eat gluten. Because this can cause irreversible damage on your intestines, testing is critical. The gold standard for testing celiac disease is small intestinal biopsy, because it will also determine the degree of damage caused by the disease. Considering how invasive a biopsy is, there are also two other types of tests: a blood test and a genetic test. Depending on your situation, your doctor may consider antibody testing adequate.

The most common food intolerances and food sensitivities

Common Food Intolerances

  • Lactose – Lactose is a sugar found in dairy products.
  • Histamine – The chemical your body produces in allergic reactions, but also present in many foods and drinks, particularly fermented foods like yogurt, cheese, wine, and sauerkraut.
  • Sulphites – A common preservative in processed foods.
  • Fructose – A simple sugar found in many fruits and some vegetables. In the Western diet, high fructose corn syrup has caused a dramatic increase of this sugar.
  • FODMAPsFermentable oligo-, di-, mono-saccharides and polyols. A cluster of fibers and sugars that can trigger GI symptoms in individuals with intolerances. People with FODMAP intolerances will also have fructose intolerance.

Common Food Sensitivities

  • Gluten
  • Dairy — whey and casein sensitivity
  • Chicken eggs 
  • Soy 
  • Corn 
  • Baker’s and brewer’s yeast 
  • Almond 

Food intolerance or irritable bowel syndrome (IBS)?

In most cases, it’s not necessarily one or the other. Food sensitivities and food intolerances (especially FODMAPs) often cause or co-occur with irritable bowel syndrome.

In my practice, I like to ask questions about the timing of symptoms. You may want to record your eating habits and see if there are a few common denominators. In my experience if you notice dairy, gluten, or eggs as your most common trigger, or if you’re totally unsure, IgG testing is useful. I’ve seen all the common food sensitivities with IBS. They often come with signs of a leaky gut as well.

A FODMAP intolerance is also common in people with IBS or small intestinal bacterial overgrowth (SIBO). If I hear a patient discuss common FODMAP triggers (“I’m eating really healthy foods, with lots of fruits and vegetables, but I’m still getting sick!”), I may suggest trying a low FODMAP diet.

Why you shouldn’t ignore a food sensitivity

If getting this through this article overwhelmed you, that’s not surprising. There may be more potential food sensitivities and food intolerances than you imagined. Moreover, there’s not one single step that will illuminate all your gastrointestinal problems. There’s a lot of trial and error.

But there’s good news too: You can see dramatic shifts in your health when you figure out the right diet for you.

My best advice to you is to work with someone who can recommend the correct testing and guide you through the process. A skilled practitioner will guide you through both the elimination diet and a therapeutic diet, as you work to restore your gut’s health.

Remember, many non-digestive symptoms (headaches, for example) start with food sensitivities. Taking the time to care for your body’s gut benefits your entire body.