Food Intolerance Word Cloud

It has been estimated that 20% of the population reports being affected by adverse reactions to certain foods. Because many individuals, (even medical professionals) may confuse or use the terms food allergy, food intolerance and food sensitivity interchangeably, I’m going to take a quick minute to define the difference.

Food Allergies vs. Food Intolerances

Simply put, food allergies stimulate an immune response that creates immediate symptoms, often within 30 minutes to 2 hours, where food intolerances may not show up for hours and are not driven by the immune system. Confusion happens when the allergies and intolerances have symptoms that overlap.

Example: Cow's Milk Allergy vs. Lactose Intolerance

A cow’s milk allergy is an allergy to the protein found in milk. It can cause gastrointestinal symptoms of abdominal pain, nausea, vomiting, diarrhea and blood or mucus in stools. It can also cause oral symptoms like swelling of the lips and tongue, and symptoms outside the GI tract, like respiratory symptoms, skin rashes or eczema and even anaphylaxis.

Lactose intolerance refers to a condition that results in symptoms occurring after ingestion of foods containing lactose - the main digestible carbohydrate (sugar) found in milk and other dairy products. A person with lactose intolerance does not produce enough lactase, an enzyme found in the small intestine responsible for digesting lactose. When lactose is unable to be digested, gut bacteria go to town feeding on it (gut bacteria LOVE carbohydrates!) and ferment it. Fermentation creates gas, which then produces abdominal pain, bloating, nausea, flatulence and diarrhea.[i]

Because both lactose intolerance and milk allergy may display overlapping symptoms of abdominal pain, diarrhea and nausea, lactose intolerance can be mislabeled as a “milk allergy”. It is important to know the clear distinctions between the two conditions, however, and the different approaches to management.

First, as I mentioned, a true milk allergy creates an immune response, where a lactose intolerance does not involve the immune system—it is simply an enzyme deficiency.

Secondly, a milk allergy generally occurs in the first year of life and can lead to malabsorption and poor weight gain. The onset of symptoms with lactose intolerance most often occurs around 5-6 years of age, however different health conditions can set the stage for enzyme deficiency later in life.

The exception to this is when we see lactose intolerance in premature infants. The intestinal cells that express the enzyme lactase are formed in the third trimester, so infants born in the second trimester may experience what is called developmental lactose intolerance; frequently detected in the first few days after birth when they begin breastfeeding or consume formula containing lactose.

Treatment also differs for a milk allergy versus lactose intolerance. With a milk allergy, complete removal of any foods containing cow’s milk is necessary, while treatment for lactose intolerance is simply a low/no lactose diet or supplementation with lactase.

Food Sensitivities

Animated woman considering food groups

That leads us to food sensitivities, a term that refers to adverse reactions to food that may involve gastrointestinal symptoms but can also include numerous other symptoms, including neurological, respiratory or musculoskeletal symptoms, behavioral and psychological symptoms, skin concerns, fatigue and headaches or migraines. That’s a BIG list!

Rather than being immediate, reactions in food sensitivities can occur hours or days later and can persist for days. Because of their delayed onset and the fact that they can share symptoms with other medical conditions, food sensitivities can be overlooked, difficult to diagnose or be misdiagnosed.

To add more to the mix, the terms food sensitivities and food intolerances are sometimes used interchangeably, as seen with the verbiage gluten intolerance or gluten sensitivity, or histamine intolerance.

Another kicker? If we go back to lactose intolerance for a second, symptoms seen in a simple lactose intolerance can vary widely between individuals and sometimes show up not only as the tell-tale gastrointestinal symptoms but also extraintestinally as headaches, vertigo, difficulty with memory and fatigue–very much like symptoms that may be seen in a sensitivity.


The diagnostic tests used to confirm a food allergy are different than those used to confirm a food intolerance or sensitivity. If your physician suspects a true food allergy, he or she will likely order a blood test to measure levels of the antibody immunoglobulin E, or IgE, which is produced in high amounts when the body has an allergic response to a food.

A second method of narrowing down food allergies is the skin prick test. For suspected lactose intolerance, a simple breath test is used to confirm a diagnosis.

Even though a food sensitivity can produce a myriad of symptoms, it is not considered an official diagnosis.

Testing for Antibodies Called IgG, IgA or IgM

Antibodies Graphic

In spite of this, testing does exist, and some companies offer diagnostic tests that look for other antibodies called IgG, IgA or IgM. My caution against relying heavily on these tests is that the body can produce some of these antibodies (especially IgG) upon simple exposure to a food. Presence of the antibodies does not necessarily indicate a sensitivity to that food. These tests can produce false-positive and false-negative results and I have yet to see consistent clinical results that support their reliability.

Even though results are not always consistent some practitioners will use these tests to stay out of the weeds and avoid the long road of a guessing game. Some of the tests rank a person’s sensitivity to a particular food by color—red (high sensitivity), yellow (moderate to mild sensitivity) and green (little to no sensitivity). Avoiding foods in the red may be a good starting point for some patients.

The "Gold Standard" to Determine Possible Food Sensitivities

The “gold standard” to determine possible food sensitivities, however, is not an expensive test at all. It is simply 100% elimination of a suspected food.

All sources of a suspect food or ingredient are avoided for a period of time and then reintroduced. For example: If dairy is the suspected culprit, all sources of dairy would be removed from the diet for approximately 4-6 weeks. After the elimination period, the person then “challenges” the body by loading up on dairy by having 3-4 servings of it in one 24-hour period, and then monitoring the response in their body over the next 3-5 days.

Completely eliminating a common food is often difficult for most people as it takes planning and seeking out alternate foods. When my patients are in the elimination phase, I encourage them to track their food intake and monitor their energy, mood, sleep and other symptoms they came to me with. Sometimes the changes are profound, sometimes they are small and incremental as the body begins to heal from no longer being insulted by the offending food. The keys are to totally eliminate a food (no cheating) and track your symptoms. If you cheat, you have to start all over again.

It may be challenging, but the discovery of your body’s relationship to a particular food can be life-changing and a big step toward healing and wellness.

If you feel that you have food allergies, food sensitivies or food intolerances, but don't know where to start, contact me for a consultation.

[i]Di Costanzo M and Canani RB. Lactose Intolerance: Common Misunderstandings.  Ann Nutr Metab.  2018. Suppl 4: 30-37. Doi: 10.1150/000493669.