Do food sensitivity blood tests work?

salad with beets, goat cheese, walnuts, oranges, greens

If you’ve been curious about food sensitivities, you’ve probably found many options while searching online. There’s everything from blood tests to hair and fingernail analysis to facial thermography. 

The most popular in recent years has been IgG blood tests. This is a test used commonly by functional medicine practitioners, and people are now able to self-order them, which has made them more prevalent than ever. 

These tests claim to measure IgG antibodies in response to specific foods. The idea is that if you are sensitive to a food, you’ll have higher IgG levels to it. But does the science back these up, and are they an accurate way of assessing food sensitivities? Let’s dive in.

Is IgG Testing Validated?

Unfortunately, IgG testing is not validated in the scientific literature as a reliable way of showing food sensitivities. Many major organizations agree. For instance, the American Academy of Allergy, Asthma and Immunology, European Academy of Allergy and Clinical Immunology, and Canadian Society of Allergy and Clinical Immunology all advise against taking these tests. 

The very few clinical studies that do exist on IgG testing show weak associations between symptom improvement and IgG food eliminations. Even in one study looking at food elimination based on IgG tests across patients with Irritable Bowel Syndrome, it’s difficult to draw solid conclusions. The people on the IgG elimination diet may have had more symptom relief compared to the placebo group because the placebo group was still eating common IBS triggers, such as dairy and gluten. This alone cannot clearly point to IgG testing as a valuable tool.

The most worrisome part about these tests is that they often give false positives. This means people tend to eliminate more foods than is actually necessary. When we already have to eliminate gluten for a medical reason, layering extra and unnecessary food restrictions can further compromise physical health and emotional well-being.

Is it Food Sensitivities, or is it Leaky Gut?

Furthermore, when a test comes back with a long list of flagged foods, it may be more a sign of leaky gut than anything else. Leaky gut is when your gut lining becomes permeable to the point where undigested food particles can get out into your bloodstream. Because these food particles shouldn’t normally access your circulation, your immune system “tags” the foods as foreign and may create antibodies against them.

Leaky gut is very common in those with functional gut disorders and dysbiosis (a fancy word for when your gut is “out-of-whack”). If someone is having chronic digestive issues, there is a very high chance they also have leaky gut. Leaky gut causes people to be far more reactive to food than they should be. Correcting the dysbiosis can heal up the leaky gut, which can help one tolerate more foods.

Bottom line: Currently, there are not enough strong studies to support IgG testing as a reliable way to find food sensitivities. We simply cannot conclude that elevated IgG levels have a pathological basis. In many cases, they can actually cause more restriction that puts people at greater risk for nutrient deficiencies and food fear/stress. In my practice, I do not regard them as a relevant way of determining food sensitivities, nor are they a sound basis on which people should eliminate more foods.

shakshuka with bread

What to Do Instead:

The current gold standard for food sensitivities is to follow an elimination/reintroduction challenge under guidance. That way you can assess one food at a time and how it affects your body. It takes longer than a blood test, but your results are more accurate and can make the difference between, for example, thinking you have a sensitivity to 10 foods versus knowing you’re sensitive to 2.

Different types of elimination/reintroduction diets can also tell you MORE than a food sensitivity blood test can. That’s because they can isolate different parts of food, such as histamine, salicylates, fermentable fibers (FODMAPs), fructose, and other components that can trigger reactions. Elimination/reintroduction challenges are one tool I use in my practice, as needed.

Finally, it’s important to remember that there are so many other reasons for digestive issues beyond true food sensitivities. Sometimes gut issues are completely unrelated to any specific food. 

For instance, some symptoms that may appear as food sensitivities are actually a sign of gut dysbiosis (and leaky gut, as mentioned). When the gut gets overrun by “bad” guys, it becomes more reactive in general, and it may seem that anything you eat gives you trouble. In this very common case, it’s necessary to re-balance the gut to start tolerating more foods. 

Sometimes, gut issues are caused by food AND another underlying issue. When food sensitivities are part of the picture, they are often only one piece. To get a better glimpse into other factors that cause persistent gut issues, make sure to grab my free guide of 15 Reasons for Continued Gut Issues.

Note: Food sensitivities are different than true food allergies. Allergies are overseen by completely different antibodies, called IgE antibodies. They typically have immediate, severe reactions. They can be diagnosed by getting a skin prick test and/or IgE test from your doctor, who may have you do an elimination diet as well.

Ironically, there is some research showing that one subset of IgG antibodies can actually protect against true IgE allergy. In fact, infants with high levels of IgG to certain foods appear to tolerate those foods better later in childhood. Research like this suggests that IgG levels on food sensitivity tests may indicate tolerance, not sensitivity!

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