Why can I suddenly not tolerate foods I used to eat?

Sudden reactions to familiar foods usually signal a shift in the gut and immune system. Common drivers include increased intestinal permeability, gut microbiome imbalance, digestive enzyme deficiency, and stress that slows or alters digestion. Infections, antibiotics, or hormone changes can also tip this balance.

What changed, and why now?

Your digestive system is an ecosystem. When the gut lining gets irritated or the microbiome shifts, foods that were once neutral can start “pinging” your immune system. Stress alone also diverts blood flow from digestion and can loosen tight junctions in the gut lining, creating more contact between food particles and immune cells. As a functional medicine practitioner, I look upstream to see which domino fell first and what combination of dominos might be involved!

Common root causes of new food reactions

  • Leaky gut, also called increased intestinal permeability. A compromised barrier lets undigested food fragments slip through, which can provoke symptoms like bloating, rashes, headaches, or fatigue, and immune reactions
  • Dysbiosis. After antibiotics, illness, or major dietary shifts, an overgrowth of certain microbes can ferment foods, generate gas, or produce histamine, making previously easy foods tough to tolerate.
  • Post-infection or after high stress. A stomach bug, travel illness, or a high-stress season can reset digestion. Some people develop post-infectious IBS, which often pairs with new food sensitivities.
  • Hormones and enzymes. Perimenopause, thyroid shifts, or declining enzymes like lactase can make dairy or other foods problematic, even if they were fine before.
  • Motility changes. Slower transit means more fermentation time and more symptoms from otherwise healthy foods.

Why simply avoiding more foods can backfire

Short-term relief is fine, but long-term restriction shrinks diet diversity, which can further narrow the microbiome and immune tolerance. The goal is not a tiny safe list. It is to calm inflammation, repair the barrier, and retrain digestion so you can bring foods back methodically without flare ups. Food sensitivities are often not a lifelong sentence! I tell my patients it’s “often not the foods fault”. At Dr. Kenny’s clinic we combine data with practical steps, so you are not stuck playing food roulette.

How I help you rebuild tolerance

1) Test, do not guess. We start with a deep history, a food and symptom timeline, and, when appropriate, targeted labs. Examples include:

  • Functional GI testing to assess inflammation, digestion, and dysbiosis.
  • Organic Acids Testing for mitochondrial stress, B-vitamin needs, and microbial byproducts.
  • Expanded thyroid and adrenal assessment if energy, questionable stress tolerance or burden, temperature sensitivity, or menstrual shifts accompany your symptoms.

2) Stabilize digestion first. Simple wins matter. Eat in a relaxed state, chew thoroughly, and balance blood sugar with protein and fiber each meal. We support stomach acid or enzymes if testing or history suggests they are low.

3) Repair and rebalance. We restore the gut barrier with the right nutrition and targeted supplements matched to your labs and story. If stress is a major trigger, we address nervous-system tone, sleep, and realistic pacing because stress chemistry changes the gut.

4) Reintroduce methodically. Once the gut is calmer, we bring foods back in a stepwise plan, starting with easiest wins. As a functional medicine practitioner, I guide this process so you can enjoy variety again with confidence.]

Additional Resources:

Ready to stop shrinking your food list and start rebuilding tolerance with a plan that fits your life?

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Answered by Dr. Kenny Mittelstadt, DACM, DC, IFMCP
Certified functional medicine practitioner specializing in advanced lab testing and personalized healing protocols to uncover root causes of health roadblocks.

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