You're Reacting to Foods, But Nobody Knows Why. Your Genes Do.

HLA-DQ2 is an immune receptor that sits on the surface of your gut-associated immune cells. Its job is to present food proteins to your immune system so it can decide whether to attack or tolerate them. When HLA-DQ2 is present, it presents gluten peptides in a way that flags them as threats.

Roughly 25-30% of people with European ancestry carry HLA-DQ2. Carrying this gene doesn’t mean you have celiac disease, but it’s a prerequisite for developing it. If you have HLA-DQ2 and your immune system develops antibodies against gluten, your intestinal lining gets attacked and damaged, which prevents nutrient absorption and causes inflammation.

You might experience bloating after bread, fatigue after pasta, digestive distress after hidden gluten in sauces or processed foods, and a sense that your body is reacting to something you can’t quite name. If you have HLA-DQ2, you’re in the high-risk group for celiac disease, but you’re also more likely to have non-celiac gluten sensitivity, where you react to gluten without having the intestinal damage.

LCT regulates lactase, the enzyme that breaks down lactose, the main sugar in milk. In infants, everyone produces lactase because breast milk is their primary food. But for most humans, lactase production naturally declines after childhood as the body stops needing to drink milk. LCT controls whether your body continues making lactase into adulthood.

Approximately 65% of the global population has the C/C genotype at rs4988235, which means lactase production declines progressively after childhood. If you carry the C/C genotype, you’re lactose non-persistent, meaning your gut cannot efficiently digest milk sugar in adulthood. This is the normal human state, not a deficiency or disease.

You might notice bloating, gas, or digestive discomfort 30 minutes to 2 hours after consuming milk, cheese, ice cream, or cream-based foods. You may have thought this was a general food sensitivity or that something was wrong with you. The truth is simpler: your body stopped making the enzyme needed to digest that particular food, exactly as it was genetically programmed to do.

FUT2 encodes a fucosyltransferase enzyme that determines what antigens appear on the surface of your gut lining cells. This controls which bacteria can colonize your gut and how your immune system learns to recognize your microbial residents. FUT2 also affects how efficiently you absorb vitamin B12 from food.

Approximately 20% of people are non-secretors, meaning they carry the reduced-function variant at rs601338. Non-secretor status shifts your gut microbiome composition in ways that can make you more susceptible to certain food reactions and less able to absorb B12 from animal products. This affects the types of bacteria that thrive in your gut and alters your immune tolerance to food antigens.

You might experience unpredictable food reactions despite keeping your diet consistent, feel fatigued despite eating enough (due to B12 absorption issues), or notice that probiotics don’t seem to help because the beneficial bacteria can’t establish themselves in your microbiome. Your gut may also be more vulnerable to norovirus and other infections because your microbial community isn’t as well-established.

MTHFR encodes methylenetetrahydrofolate reductase, an enzyme that converts dietary folate into methylfolate, the form your cells can actually use. This enzyme is critical for converting B vitamins into energy, building neurotransmitters, and supporting your immune system’s ability to distinguish between self and non-self.

The MTHFR C677T variant, carried by approximately 40% of the population, reduces enzyme efficiency by 40-70%. If you carry one or two copies of this variant, you’re converting dietary folate into usable methylfolate at a fraction of the rate you should be, leaving your cells functionally depleted at the biochemical level. This affects your immune tolerance to food proteins and your ability to mount appropriate (not excessive) inflammatory responses.

You might experience food reactions that don’t correspond to any specific foods you can identify, feel tired despite eating well, have unexplained bloating or gas, or find that your food sensitivities seem to worsen during periods of high stress (when your body’s methylation demands increase). Your immune system may be unable to properly regulate its response to food antigens, leaving you vulnerable to developing new sensitivities.

TNF encodes tumor necrosis factor-alpha, a cytokine that signals immune cells to mount inflammatory responses. TNF is essential for fighting infections, but when it’s produced excessively, it damages your intestinal lining by increasing permeability (the spaces between cells in your gut wall get wider), allowing undigested food particles to leak into your bloodstream where they trigger immune reactions.

Approximately 30% of the population carries the A allele at rs1800629, which is associated with higher TNF-alpha production. If you carry this variant, your gut lining is genetically prone to leaking, which means food proteins that should stay in your digestive tract instead enter your bloodstream and trigger immune reactions. This is the mechanism behind “leaky gut” and is a major driver of food sensitivities.

You might experience seemingly random food reactions, bloating and gas after meals despite eating foods that usually don’t bother you, fatigue that worsens after eating, or a sense that your gut is increasingly reactive and unpredictable. You may also notice that your sensitivities develop gradually over time as your intestinal barrier becomes progressively more permeable.

IL6 encodes interleukin-6, a cytokine that coordinates immune responses and amplifies inflammation. While IL-6 is necessary for fighting infections and healing injuries, excessive IL-6 production keeps your immune system in a state of constant alert, making it hyperresponsive to food proteins and environmental triggers.

Variants in the IL6 promoter region affect how easily your immune cells turn on IL-6 production. If you carry a variant associated with higher IL-6 expression, your immune system mounts disproportionately large inflammatory responses to food antigens, turning minor exposures into major symptoms. Your food sensitivities aren’t due to the food itself; they’re due to your immune system’s excessive reaction to it.

You might experience severe reactions to small amounts of trigger foods while others can tolerate them easily, notice that your sensitivities worsen during stressful periods (when IL-6 is already elevated), or feel like your immune system is constantly activated. Your reactions might include not just digestive symptoms but also systemic inflammation: joint pain, brain fog, or skin reactions after eating certain foods.