June 10, 2022 - Written By: Maria Arini Lopez, PT, DPT
Many people experience uncomfortable sensations or reactions after eating—from diarrhea, stomach pain, and abdominal bloating to lip, tongue, or facial swelling to skin rashes, a runny nose, and watery eyes to the more extreme and serious swelling of the throat and mouth accompanied by trouble breathing (anaphylaxis).1
So, how exactly can you tell the difference between a food allergy, sensitivity, and intolerance when so many symptoms seem to overlap?
Some of these symptoms are caused by an immune system response to the food, while others are caused more by a reaction of your digestive system.
A bit about the immune system…
The immune system produces white blood cells which protect and defend the human body against foreign substances like bacteria and viruses. Occasionally, the body mistakenly considers certain foods as foreign invaders and these white blood cells wage war against the food molecules. Plasma cells are white blood cells that produce antibodies, proteins known as immunoglobulins, which attack the food molecules.2
The 5 Immunoglobulin Classifications
There are 5 different types of immunoglobulins: immunoglobulin G (IgG), immunoglobulin M (IgM), immunoglobulin A (IgA), immunoglobulin D (IgD), and immunoglobulin E (IgE). Normally, IgG, IgM, and IgA antibodies are found most frequently in the human body. Various combinations of these antibodies circulate throughout your body with IgG accounting for 85%, IgA accounting for 15%, and IgM accounting for 13-15% of human antibodies. The rarer antibodies, IgD and IgE, account for 0.2% and 0.002% of human antibodies, respectively.3
Food allergies are the most serious category. Food allergies occur when your immune system responds immediately, sometimes in exaggerated ways, by sending in IgE antibodies to take care of the “foreign invader”—whatever specific food you ate.4
IgE antibodies can also release large amounts of histamine when they and the allergen bind to and activate cells called mast cells. Masts cells are white blood cells located throughout the digestive tract, skin, lungs, and all connective tissues.5,6,7
If you have severe food allergies (most often caused by peanuts, tree nuts, milk, eggs, wheat, soy products, fish, and shellfish among others), you may experience anaphylaxis. During anaphylactic shock, your throat constricts, resulting in trouble breathing, lightheadedness, confusion, rapid heartbeat, clamminess of the skin, and, if not immediately treated, loss of consciousness.1,4 Anaphylaxis is related to the systemic, multiorgan release of histamine by mast cells.7 When severe food allergies become known, doctors recommend that you always carry an EPI-pen (usually two in case one doesn’t work) to self-administer during anaphylaxis.
With milder food allergies that are IgE-mediated, you may experience oral allergy syndrome (localized swelling and symptoms of the lips, mouth, and throat), a runny nose, flushing, hives, asthma, acute vomiting, nausea, or diarrhea. These reactions usually occur immediately after eating the food.1,4,8
Doctors who are trained allergists/immunologists can determine if you have food allergies by running blood tests to detect IgE antibodies after you eat certain foods that cause reactions. They may also perform skin prick tests. Small amounts of the foods that are being assessed are placed in liquid on top of your skin which is then pricked, allowing entry of the food into the skin. A growing bump that turns red indicates a positive skin test.8
Two recent 2018 studies estimated that IgE-mediated food allergies affect 1 in 10 adults and 1 in 12 children in the US.9
Food sensitivities are often the result of IgG- or IgA-driven immune system responses which are more delayed compared to the immediate IgE response in true food allergies. These delayed responses may occur hours or even days after eating a food to which you are sensitive.10,11 Symptoms include brain fog, fatigue, headaches, joint pain, skin reactions (rashes), and stomach bloating or pain.1,10
One way to determine if you are sensitive to specific foods is to try an elimination diet. Common food sensitivities include gluten and dairy. During an elimination diet, you completely stop eating these common triggers or other foods that you suspect might contribute to your symptoms for at least a couple of months.1
It is important to be consistent with avoiding these foods for this long. This is because IgGs last longer in the body (between 21 and 28 days) compared to IgAs (3 days) and IgEs (2 days).11,12 You want to completely clear these circulating antibodies from your system to get an accurate idea of how you feel without any residual immune system response.
Then, reintroduce these foods one by one back into your diet while keeping notes on any symptoms or reactions your body has. This way, you can clearly identify the foods which are triggers.1
Food sensitivities usually provoke milder reactions than food allergies or intolerances. These responses may fluctuate depending on the changes that occur in the gut microbiome. This often allows people with food sensitivities to still consume these triggering foods in moderation.1
Food intolerance is caused by a person’s inability to digest specific foods or food components, most notably lactose (lactose intolerance) or gluten (Celiac disease).1,11 Food intolerances usually involve localized digestive system responses as opposed to immune system responses (with the unique exception of Celiac disease).
Someone who is lactose intolerant does not produce enough of the enzyme, lactase, which is needed to digest lactose, a sugar found in milk products.13 Lactose intolerance can be diagnosed following a lactose breath test, lactose-tolerance test, or a stool PH test.1
Celiac disease is unique in that it is a food intolerance that provokes an autoimmune response every time someone with Celiac disease eats gluten-containing substances such as barley, wheat, or rye. During the autoimmune reaction, the immune system targets and locally damages the inner lining of the person’s small intestine, which then interferes with absorption of other nutrients.14 Celiac disease is diagnosed following blood tests to detect antibody levels, biopsies of the small intestinal lining, or genetic testing.15
Symptoms of a food intolerance often appear 30 minutes to 2 hours after eating or drinking because this is the estimated time it takes for the substance to reach the stomach and small intestine. However, sometimes these symptoms may appear a few days later. Symptoms of a food intolerance are generally localized to the digestive system, including diarrhea, indigestion, stomach pain or bloating, abdominal distension, nausea, vomiting, or gas.13,14
It is estimated that 75% of the global population is lactose intolerant.16 Celiac disease is less common, occurring in 1.4% of every 275,818 people. Increasing prevalence of Celiac disease is found in children compared with adults.17
It is important to differentiate between food allergies, food sensitivities, and food intolerances. Consultations with an allergist/immunologist and a gastroenterologist (digestive system specialist) may help you to figure out exactly why you are having the symptoms you do after consuming certain foods. They can also help you to implement a treatment plan to manage or completely avoid these reactions. If you can’t eat certain foods, consulting with a nutritionist might be helpful to figure out ways in which you can still get adequate amounts of the nutrients you need while avoiding food triggers.
It has been said that the gut is the “second brain,” so it is vital to take good care of it.
References and Resources
Food Sensitivity vs Allergy vs Intolerance: Understand the Differences Between Uncomfortable Symptoms Following Meals. Westside Head and Neck. Accessed May 27, 2022.
Introduction to immunoglobulins. ThermoFisher Scientific. Accessed May 27, 2022.
Beck K. What are the five classes of immunoglobulins? Sciencing. Accessed May 27, 2022.
Gargano D, Appanna R, Santonicola A, et al. Food Allergy and Intolerance: A Narrative Review on Nutritional Concerns. Nutrients. 2021;13(5):1638. doi:10.3390/nu13051638
Mast cell activation syndrome (MCAS). American Academy of Allergy Asthma and Immunology. Accessed May 27, 2022.
Definition of mast cell. National Cancer Institute. Accessed May 27, 2022.
Kanagaratham C, El Ansari YS, Lewis OL, Oettgen HC. IgE and IgG Antibodies as Regulators of Mast Cell and Basophil Functions in Food Allergy. Front Immunol. 2020;11:603050. doi:10.3389/fimmu.2020.603050
Testing for food allergies. WebMD. Accessed May 27, 2022.
Warren CM, Jiang J, Gupta RS. Epidemiology and burden of food allergy. Curr Allergy Asthma Rep. 2020;20(2):6. doi:10.1007/s11882-020-0898-7
Understanding Food Allergy and Food Sensitivity (IgA vs IgG vs IgE reactions). Naturopathic Pediatrics. Accessed June 1, 2022.
Missimer A. Are you suffering from food intolerances? The Movement Paradigm. Published March 14, 2022. Accessed May 27, 2022.
Halflife of Antibodies - Molecular Immunology. Arthritis Research. Accessed June 1, 2022.
Lactose intolerance - symptoms and causes. Mayo Clinic. Accessed June 1, 2022.
Celiac disease - symptoms and causes. Mayo Clinic. Accessed June 1, 2022.
Diagnosis of Celiac Disease. National Institute of Diabetes and Digestive and Kidney Diseases - National Institutes of Health. Accessed June 1, 2022.
What is the global prevalence of lactose intolerance? Medscape. Accessed June 1, 2022.
Singh P, Arora A, Strand TA, et al. Global Prevalence of Celiac Disease: Systematic Review and Meta-analysis. Clin Gastroenterol Hepatol. 2018;16(6):823-836.e2. doi:10.1016/j.cgh.2017.06.037
Maria Arini Lopez, PT, DPT
Maria Arini Lopez, PT, DPT, CSCS, CIMT, CMTPT is a freelance medical writer and Doctor of Physical Therapy from Maryland. She has expertise in the therapeutic areas of orthopedics, neurology, chronic pain, gastrointestinal dysfunctions, and rare diseases, especially Ehlers Danlos Syndrome.