why you probably don’t need that food sensitivity test
meet Emma
Emma walked into my office clutching a thick packet of lab results from an at-home food sensitivity test she'd ordered after getting ads for it on Instagram. The test showed reactions to 18 different foods - spinach, sesame seeds, almonds, eggs, salmon... the list went on and on.
She'd been dealing with uncomfortable bloating for years and was ready to do anything to make it stop. She been following the elimination diet for three weeks and felt more restricted and anxious about food than ever. "I don't know what to eat anymore," she told me. "I'm afraid everything is making me sick."
Sound familiar?
the science behind IgG food testing
To understand why IgG food testing is problematic, we need to look at what's actually happening in your immune system when you eat. Your body has several different types of antibodies, which basically function as your immune system's security guards. Each type has a different job.
IgE antibodies are the ones involved in true food allergies - the immediate, sometimes life-threatening reactions like swelling, hives, or anaphylaxis. These responses happen within minutes and are what we test for when diagnosing genuine food allergies. The classic example of this is a peanut allergy.
IgG antibodies, on the other hand, have a completely different role. They're part of your body's normal, healthy immune response to ANY protein you eat regularly. When you consume food proteins (whether it's salmon, spinach, or almonds) small amounts of these proteins naturally cross through your gut lining into your bloodstream. This is normal and expected.
Your immune system recognizes these food proteins as foreign substances and creates IgG antibodies as a memory response. This is actually a sign of immune tolerance, not reactivity. The more frequently you eat a particular food, the higher your IgG levels will be for that food. It's your immune system saying "I recognize this, it's safe."
So, here's the problem with IgG testing: the foods showing the highest IgG levels are typically the foods you eat most often. If you have eggs for breakfast every single morning, your IgG levels to eggs will be elevated. If you eat salmon twice a week, you'll could have detectable IgG antibodies to salmon. This doesn't mean these foods are causing inflammation or health problems! It means your immune system is doing exactly what it should be doing.
This is why IgG tests often show the strongest reactions to whatever foods dominate your diet. Which can mean that you're showing an IgG response to food that is NOT necessarily a "problem food." The less varied your eating habits, the more concentrated your IgG responses will be to those repeated foods.
Someone eating the same rotation of meals week after week will show higher IgG levels to those specific foods simply because of the repetitive exposure, not because those foods are problematic.
What's particularly concerning is how this normal immune function gets misinterpreted. Companies marketing these tests suggest that IgG positivity indicates inflammation, food sensitivity, or the need for elimination. But research shows that people without any digestive symptoms have the same IgG patterns as those with symptoms (PMID 36147305). In fact, a 2025 study suggests that higher IgG levels to foods may actually be protective and associated with better immune tolerance.
So, here's the deal: IgG testing is measuring your body's normal, healthy response to the foods you eat regularly. If you come back with an elevated IgG to a specific food, I probably won't tell you to cut it out entirely. Instead, we'll focus on what else you can include, NOT what you need to take away.
variety > restriction
Your body thrives on diversity, and eating the same foods repeatedly can actually create the very sensitivities we're trying to avoid. When you have oatmeal every morning and rotate between the same three dinners, you're putting constant pressure on your digestive system to handle the same proteins over and over. With this repetitive exposure, your digestive system becomes overworked. What once was well-tolerated can start triggering symptoms. Food rotation gives your gut a break and feeds your microbiome the variety it needs to maintain the diverse bacterial ecosystem that's so very important for health and longevity.
the restriction/fear cycle
Food restriction has a way of snowballing that's both physiologically and psychologically destructive. When someone like Emma gets a test showing reactions to 18 foods and eliminates them all at once, several problematic things happen simultaneously.
Physical impact: suddenly removing multiple foods creates nutritional gaps. Maybe she's eliminated her main sources of omega-3 fatty acids (salmon!), or her primary vegetables, or her go-to proteins. Her body is now running on a limited fuel mix, often leading to increased cravings, energy crashes, and actually more digestive upset as her system tries to adapt to the dramatic change.
Digestive issues: when you stop eating certain foods completely, your body stops producing the specific enzymes needed to break them down efficiently. It can be a"use it or lose it" situation. So when Emma eventually tries to reintroduce salmon after months of avoidance, she might actually experience digestive discomfort - not because salmon is inherently problematic for her, but because her digestive system is out of practice.
Microbiome disruption: remember those beneficial bacteria that thrive on variety? When you eliminate multiple food groups, you can starve certain populations of gut bacteria. This can actually create more digestive sensitivity, not less. You might eliminate tomatoes to "heal your gut," but in the process, you lose the bacteria that help you digest the compounds in nightshade vegetables.
The psychological impact: This is perhaps the most damaging. Food becomes the enemy. When you're anxious about food, you're in sympathetic overdrive ("fight or flight"). In this state, your digestion actually shuts down. Stomach acid production decreases, digestive enzymes drop, and gut motility slows. Every meal becomes a source of anxiety rather than nourishment and pleasure.
I've had clients who started carrying lists of "safe" foods, who stopped eating at restaurants, who declined social invitations because they were afraid of the food that might be served. Unfortunately, this isn't really healing anything. Cutting everything out of your diet and having your symptoms go away is. not. healing.
This is actually the opposite of what your body needs. Your gut wants to be resilient and adaptable. It wants to handle a wide variety of nourishing foods with ease. But resilience comes from gentle, gradual exposure to diversity, not from restriction and avoidance.
True gut healing means cultivating a robust and diverse microbiome that can handle the beautiful variety of foods this world offers. A truly healthy gut should be able to enjoy the occasional slice of pizza or bowl of ice cream without sending your body into chaos - that's resilience, not restriction.
what I recommend instead
Instead of asking "what foods are you reacting to," I prefer to ask "what's actually happening in your gut?" This is where comprehensive gut microbiome testing becomes invaluable. I use the GI MAP in my practice to find out:
Do you have leaky gut or compromised intestinal barrier integrity?
Is your immune function impaired due to gut inflammation?
Are you missing key beneficial bacteria like Akkermansia muciniphila that maintains your gut lining?
Do you have enough of the good gut bacteria (like Faecalibacterium and Roseburia) that turn fiber into anti-inflammatory compounds to keep your gut and body healthy?
What pathogens, fungi, or parasites might be creating inflammation?
How well are you actually digesting and absorbing nutrients?
This approach gives us actionable information about what actually needs healing, rather than just creating a long list of foods to avoid.
back to Emma's story:
When I ran Emma's GI MAP, we discovered she had virtually no Akkermansia, very low beneficial bacteria diversity, elevated inflammatory markers, and signs of leaky gut. No wonder she was reacting to so many foods! Instead of restricting more foods, we focused on decreasing inflammation in her gut, healing her intestinal lining, and rebuilding her microbiome diversity. Four months later, she was eating a varied, colorful diet again (including all of those "reactive" foods from her sensitivity test) - and, most importantly, she was feeling better than she had in years. We love to see this!
