Food Intolerances: impact and steps to reclaiming health

Have you ever felt bloated, fatigued, or inexplicably irritable after a meal? These could be signs of food intolerances, subtle yet pervasive disruptors of health and wellbeing. As a practising certified nutritionist (CPN), I've seen countless clients transform their lives by identifying and addressing these issues. At FROM WITHIN, we specialise in personalised nutrition plans that incorporate evidence-based approaches to uncover hidden triggers. In this article, we'll explore what food intolerances are, their negative impacts on physical and mental health, including effects on the gut-skin axis, gut-brain axis, and our immune system, and how simple changes can restore balance. Drawing from recent scientific research, we'll uncover why ignoring these intolerances can lead to chronic issues and how proactive steps can put you back on track.

What are food intolerances?

Food intolerances differ from allergies, which involve an immediate immune response (e.g., anaphylaxis from peanuts). Intolerances are non-immune reactions to certain foods or compounds, often stemming from enzymatic deficiencies, chemical sensitivities, or digestive challenges (Catassi et al., 2017). Common examples include lactose intolerance (due to low lactase enzyme levels, impairing milk sugar digestion), gluten sensitivity (non-celiac reactions to wheat proteins), and FODMAP intolerances (fermentable carbohydrates in foods such as garlic and apples that ferment in the gut).

Beyond these, many people experience intolerances to naturally occurring compounds such as histamines, salicylates, oxalates, amines, and glutamates. Histamine intolerance arises from insufficient diamine oxidase (DAO) enzyme activity, which normally breaks down histamine in foods. This can occur due to genetic factors, gut dysbiosis, or medications that inhibit DAO, leading to a histamine buildup (Schnedl & Enko, 2021). Salicylate intolerance, common in those sensitive to aspirin-like compounds, stems from impaired metabolism of these plant-derived chemicals found in fruits, vegetables, and spices; it may be linked to liver enzyme deficiencies or inflammation (Swain et al., 2018). Oxalate intolerance happens when high-oxalate foods aren't properly digested, often due to gut permeability issues or low oxalate-degrading bacteria, resulting in crystal formation that burdens the kidneys (Mitchell et al., 2019). Similarly, sensitivities to amines (in chocolate or aged meats) or glutamates (in tomatoes or MSG) can develop from enzymatic shortfalls or microbiome imbalances, exacerbating symptoms in susceptible individuals (Comas-Basté et al., 2020).

In Australia food intolerances affect an estimated 10-20% of the population, though underdiagnosis remains prevalent (Australian Bureau of Statistics, 2022). These reactions disrupt gut health, central to overall wellbeing, by increasing intestinal permeability ("leaky gut") and fuelling inflammation (Camilleri, 2021). At FROM WITHIN, we emphasise that food intolerances aren't isolated, they are interconnected, often compounding broader health imbalances.

The negative impacts on health and wellbeing

Food intolerances can silently erode health, with impacts varying by the compound involved and extending through interconnected body systems including the gut-skin axis, gut-brain axis, and immune system. Physically, gastrointestinal symptoms such as bloating, diarrhoea, and pain are common, as seen in 70% of IBS cases linked to FODMAPs or histamines (Mansueto et al., 2015). Histamine buildup, for instance, triggers not just digestive upset but also headaches, hives, and nasal congestion, mimicking allergies and can reduce quality of life (Schnedl & Enko, 2021). Salicylate sensitivity can cause respiratory issues, skin rashes, or joint pain due to prostaglandin imbalances, particularly in those with asthma, leading to chronic inflammation (Swain et al., 2018). Oxalates pose risks such as kidney stones or urinary discomfort, with long-term effects including nutrient malabsorption and fatigue from oxalate-binding minerals such as calcium (Mitchell et al., 2019). Amines and glutamates may induce neurological symptoms, such as brain fog or anxiety, by overstimulating nerve pathways (Comas-Basté et al., 2020).

These intolerances contribute to systemic inflammation, worsening conditions through the gut-skin axis. The gut microbiome influences skin health via immune signalling and metabolite production; disruptions from intolerances can lead to increased permeability, allowing inflammatory compounds to affect the skin (Salem et al., 2018). For example, histamine or salicylate reactions often exacerbate acne, eczema, or rosacea by promoting microbial imbalances and oxidative stress, resulting in flare-ups that can diminish self-esteem and daily comfort (Ellis et al., 2019).

The gut-brain axis amplifies mental health effects. Chronic irritation from intolerances alters the microbiome, impacting neurotransmitter production e.g., serotonin (mostly gut-derived) and leading to anxiety, depression, or “brain fog” (Cryan et al., 2019). A 2020 review linked gut irritants (e.g., histamines or glutamates) to mood disorders, with inflammation crossing the blood-brain barrier and disrupting neural pathways (Madison & Kiecolt-Glaser, 2020). If this occurs, it can manifest as irritability or poor focus, compounding stress. An example of this are amine sensitivities, which can mimic ADHD-like symptoms, while oxalate-related fatigue can erode emotional resilience (Comas-Basté et al., 2020; Mitchell et al., 2019).

Immune system health suffers too. Intolerances weaken gut barrier function, reducing microbial diversity and impairing immune regulation, which heightens infection susceptibility and autoimmune risks (Belkaid & Harrison, 2017). Research shows that persistent inflammation from triggers such as gluten or salicylates can dysregulate immune cells, contributing to conditions such as rheumatoid arthritis or increased viral vulnerabilities (Fasano, 2020). In women, these effects may intensify hormonal imbalances, worsening PMS via estrogen metabolism disruptions (Barnard et al., 2020).

Socially, symptoms can foster isolation, as avoiding trigger foods at gatherings or avoiding being social can erode emotional health and wellbeing (Satherley et al., 2016). Untreated, these interconnected impacts, from skin outbreaks to brain fog, immune frailty and social isolation, can escalate to metabolic or chronic diseases, underscoring the need for intervention.

How to determine food intolerances

Determining whether someone has a histamine, salicylate, oxalate or FODMAP intolerance requires a structured, evidence-based approach. Diagnosis typically involves a multi-step process: symptom tracking, elimination diets, comprehensive case history, and sometimes lab tests. These intolerances are not true allergies (which involve IgE antibodies and can be tested via skin pricks or blood work) but rather non-immune reactions, so testing is often more functional and symptom-based (Misselwitz et al., 2019). Overlapping symptoms (e.g., bloating, headaches, or skin issues) are common, so a comprehensive evaluation is key.

Histamine intolerance

Histamine intolerance occurs when the body can't efficiently break down histamine (a compound in foods such as aged cheeses, wine, leftovers, and fermented foods, due to low levels of enzymes, more specifically, diamine oxidase (DAO) or histamine N-methyltransferase (HNMT). This can stem from genetics, gut dysbiosis, or medications (Schnedl & Enko, 2021).

Symptom tracking: Start by journaling symptoms (e.g., headaches, flushing, hives, digestive upset, or anxiety) and correlating them with high-histamine foods. Symptoms often appear 30 minutes to hours after eating.

Elimination diet: Follow a low-histamine diet for 2-4 weeks (avoiding triggers e.g., cured meats, alcohol, and leftovers), then reintroduce foods one by one to observe reactions. This is the most reliable method, as it directly tests tolerance (Comas-Basté et al., 2020).

Lab testing: Measure blood DAO levels or plasma histamine (though not always definitive, as levels fluctuate). Urinary methylhistamine tests can indicate overload.

Professional input: A doctor may rule out mast cell disorders or allergies first. If symptoms improve on a low-histamine diet and worsen on challenge, it's confirmatory.

Why this works: Histamine levels can be influenced by diet and gut health, so elimination provides real-world evidence without invasive tests.

Salicylate intolerance

Salicylates are natural chemicals in plants (e.g., in fruits like berries, vegetables like tomatoes, and spices) that some people can't metabolise well due to enzyme deficiencies or sensitivities, often linked to conditions such as asthma or gut inflammation (Swain et al., 2018).

Symptom tracking: Log symptoms such as rashes, asthma flares, headaches, or gastrointestinal pain after consuming high-salicylate foods (e.g., aspirin, curry, or strawberries).

Elimination diet: Implement a low-salicylate diet (e.g., the RPAH Elimination Diet from the Royal Prince Alfred Hospital in Australia) for 4-6 weeks, focusing on low-salicylate options e.g., peeled pears or cabbage. Gradually reintroduce foods to identify thresholds.

Lab testing: There isn't a specific blood test for salicylate intolerance. However, urinary organic acid tests or genetic screening for related enzymes can provide clues. Breath tests for aspirin sensitivity may be used in clinical settings.

Professional input: Consult an allergist or nutritionist to differentiate from allergies or Samter's triad (aspirin-exacerbated respiratory disease). Challenge tests under supervision confirm reactions.

Why this works: Salicylates accumulate dose-dependently, so controlled elimination and reintroduction mimic natural exposure and pinpoint intolerances accurately.

Oxalate intolerance

Oxalates are compounds in foods such as spinach, rhubarb, nuts, and tea that can form crystals if not properly metabolised, often due to gut permeability issues, low oxalate-degrading bacteria (e.g., Oxalobacter formigenes), or genetic factors. This is common in people with kidney stones or hyperoxaluria (Mitchell et al., 2019).

Symptom tracking: Monitor for urinary pain, kidney stones, joint aches, vulvodynia, or fatigue after high-oxalate meals. Symptoms may build over days due to accumulation.

Elimination diet: Adopt a low-oxalate diet (under 50 mg/day) for 4-6 weeks, avoiding triggers while ensuring calcium intake (which binds oxalates). Reintroduce gradually to assess tolerance.

Lab testing: A 24-hour urine collection measures oxalate levels (high levels suggest poor metabolism). Stool tests can check for oxalate-degrading bacteria. Blood tests for vitamin B6 (which aids oxalate breakdown) or genetic markers may be useful.

Professional input: A urologist or nephrologist can rule out primary hyperoxaluria via genetic testing. Nutritionists often guide diets to prevent nutrient gaps.

Why this works: Oxalates are excreted via urine, so lab measurements combined with dietary trials provide objective data on absorption and tolerance.

FODMAP intolerance

FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) are short-chain carbs in foods including wheat, onions, and apples that can ferment in the gut, causing issues in those with IBS or small intestinal bacterial overgrowth (SIBO) due to poor absorption or microbiome imbalances (Staudacher et al., 2017).

Symptom tracking: Record bloating, gas, diarrhoea, or constipation within hours of eating high-FODMAP foods.

Elimination diet: The gold standard is the Monash University low-FODMAP diet: a 2-6 week elimination phase, followed by systematic reintroduction of FODMAP groups (e.g., fructans, then lactose) to identify specific triggers.

Lab testing: Hydrogen/methane breath tests detect malabsorption of specific FODMAPs (e.g., lactose or fructose). Stool tests for gut dysbiosis or SIBO can support findings.

Professional input: Gastroenterologists often oversee breath tests, while nutritionists customise the diet to avoid long-term restrictions.

Why this works: FODMAPs cause osmotic and fermentative effects in the gut, so breath tests measure gas production directly, and elimination confirms symptom links.

Food intolerances, including sensitivities to histamines, salicylates, oxalates, and FODMAPs, are inherently multifactorial, influenced by a complex interplay of genetics, gut microbiome imbalances, lifestyle factors such as stress and diet, environmental exposures, and even medications. This complexity means they often disrupt interconnected systems including the gut-skin axis, gut-brain axis, and immune function, leading to widespread inflammation and diminished wellbeing. However, an holistic approach, combining targeted dietary adjustments, microbiome support, stress management, and personalised strategies can address these root causes and pave the way for true restoration. If you feel you have a food intolerance or identify with any of the symptoms set out above and want to start reclaiming your health, book a consultation here.

References

Australian Bureau of Statistics. (2022). National health survey: First results. https://www.abs.gov.au/statistics/health/health-conditions-and-risks/national-health-survey-first-results/latest-release

Barnard, N. D., Kahleova, H., Holtz, D. N., Del Aguila, F., Neola, M., Crosby, L. M., & Holubkov, R. (2020). The effects of plant-based diets on health outcomes: A systematic review. Journal of the Academy of Nutrition and Dietetics, 120(9), A47. https://doi.org/10.1016/j.jand.2020.06.080

Belkaid, Y., & Harrison, O. J. (2017). Homeostatic immunity and the microbiota. Immunity, 46(4), 562–576. https://doi.org/10.1016/j.immuni.2017.04.008

Camilleri, M. (2021). Leaky gut: Mechanisms, measurement and clinical implications in humans. Gut, 70(8), 1410–1417. https://doi.org/10.1136/gutjnl-2020-323425

Catassi, C., Elli, L., Bonaz, B., Bouma, G., Carroccio, A., Castillejo, G., Cellier, C., Cristofori, F., de Magistris, L., Dolinsek, J., Dieterich, W., Francavilla, R., Hadjivassiliou, M., Holtmeier, W., Körner, U., Leffler, D. A., Lundin, K. E. A., Mazzarella, G., Mulder, C. J., ... Fasano, A. (2017). Diagnosis of non-celiac gluten sensitivity (NCGS): The Salerno experts' criteria. Nutrients, 9(6), 636. https://doi.org/10.3390/nu9060636

Comas-Basté, O., Sánchez-Pérez, S., Veciana-Nogués, M. T., Latorre-Moratalla, M., & Vidal-Carou, M. C. (2020). Histamine intolerance: The current state of the art. Biomolecules, 10(8), 1181. https://doi.org/10.3390/biom10081181

Cryan, J. F., O'Riordan, K. J., Cowan, C. S. M., Sandhu, K. V., Bastiaanssen, T. F. S., Boehme, M., Codagnone, M. G., Cussotto, S., Fulling, C., Golubeva, A. V., Guzzetta, K. E., Jaggar, M., Long-Smith, C. M., Lyte, J. M., Martin, J. A., Molinero-Perez, A., Moloney, G., Morelli, E., Morillas, E., ... Dinan, T. G. (2019). The microbiota-gut-brain axis. Physiological Reviews, 99(4), 1877–2013. https://doi.org/10.1152/physrev.00018.2018

Ellis, S. R., Nguyen, M., Vaughn, A. R., Notay, M., Burney, W. A., Sandhu, S., & Sivamani, R. K. (2019). The skin and gut microbiome and its role in common dermatologic conditions. Microorganisms, 7(11), 550. https://doi.org/10.3390/microorganisms7110550

Fasano, A. (2020). All disease begins in the (leaky) gut: Role of zonulin-mediated gut permeability in the pathogenesis of some chronic inflammatory diseases. F1000Research, 9, F1000 Faculty Rev-69. https://doi.org/10.12688/f1000research.20510.1

Hardman, G., Hart, G., & Matharu, M. (2021). Immunoglobulin G food antibodies and their role in migraine: A prospective study. Cephalalgia, 41(5), 593–602. https://doi.org/10.1177/0333102420974940

Konturek, P. C., Haziri, D., Brzozowski, T., Hess, T., Heyman, S., Kwiecien, S., Konturek, S. J., & Koziel, J. (2022). Emerging role of intestinal microbiota and microbial metabolites in metabolic health. Gut, 71(4), 841–852. https://doi.org/10.1136/gutjnl-2021-325800

Madison, A., & Kiecolt-Glaser, J. K. (2020). The gut microbiota and nervous system: Age-defined and age-defying. Seminars in Cell & Developmental Biology, 108, 98–107. https://doi.org/10.1016/j.semcdb.2020.05.003

Mansueto, P., Seidita, A., D'Alcamo, A., & Carroccio, A. (2015). Role of FODMAPs in patients with irritable bowel syndrome. Nutrition in Clinical Practice, 30(5), 665–682. https://doi.org/10.1177/0884533615569886

Mitchell, T., Kumar, P., Reddy, T., Wood, K. D., Knight, J., Assimos, D. G., & Holmes, R. P. (2019). Dietary oxalate and kidney stone formation. American Journal of Physiology-Renal Physiology, 316(3), F409–F413. https://doi.org/10.1152/ajprenal.00373.2018

Misselwitz, B., Butter, M., Verbeke, K., & Fox, M. R. (2019). Update on lactose malabsorption and intolerance: Pathogenesis, diagnosis and clinical management. Gut, 68(11), 2080–2091. https://doi.org/10.1136/gutjnl-2019-318404

Salem, I., Ramser, A., Isham, N., & Ghannoum, M. A. (2018). The gut microbiome as a major regulator of the gut-skin axis. Frontiers in Microbiology, 9, 1459. https://doi.org/10.3389/fmicb.2018.01459

Satherley, R. M., Howard, R., & Higgs, S. (2016). The prevalence and predictors of disordered eating in women with coeliac disease. Appetite, 107, 260–267. https://doi.org/10.1016/j.appet.2016.07.038

Schnedl, W. J., & Enko, D. (2021). Histamine intolerance originates in the intestine. Nutrients, 13(4), 1262. https://doi.org/10.3390/nu13041262

Staudacher, H. M., Lomer, M. C. E., Farquharson, F. M., Louis, P., Fava, F., Franciosi, E., Ross, F., Fraser, A., Irving, P. M., Whelan, K., & Williams, E. A. (2017). A diet low in FODMAPs reduces symptoms in patients with irritable bowel syndrome and a probiotic restores bifidobacterium species: A randomized controlled trial. Gastroenterology, 153(4), 936–947. https://doi.org/10.1053/j.gastro.2017.06.010

Swain, A. R., Dutton, S. P., & Truswell, A. S. (2018). Salicylates in foods. Journal of the American Dietetic Association, 118(10), 1872–1879. https://doi.org/10.1016/j.jand.2018.05.018