Food intolerance is a non-immunological response triggered by certain types of food or food components, even at doses normally tolerated by others, due to our digestive system’s inability to digest them. Approximately 15-20% of the population have a food intolerance.¹ Lactose intolerance is the most common food intolerance.

It is characterised by the inability to digest lactose, a sugar naturally found in milk and milk products, like cheese. The gut microbiome is a complex community of microorganisms that inhabit our digestive system. Recently, there has been an increasing interest in the role of gut microbiome in food intolerance.

The most common types of food intolerance and their associated symptoms

Lactose intolerance

Lactose intolerance arises from the malabsorption of lactose due to lactase deficiency, an enzyme that breaks down lactose. Symptoms of lactose intolerance include vomiting, bloating, tummy discomfort or pain, constipation or diarrhoea, cramps, and nausea. The severity of the symptoms can vary between individuals and depends on the amount of lactose consumed.

There are several known types of lactose intolerance, which are defined by their underlying causes. Primary lactose intolerance is the most common type. Patients with primary lactose intolerance produce enough lactase at the beginning of their life, but levels decline sharply when they start consuming whole foods.

This makes it difficult for them to digest milk and dairy products. Another type is secondary lactose intolerance, which occurs when lactase levels decrease after illness. Conditions thought to trigger secondary lactose intolerance include celiac disease, intestinal infection, Crohn’s disease, ulcerative colitis, inflammatory bowel disease (IBD), bowel infections, bowel surgery, and injury.

Chemotherapy may also contribute to the development of secondary lactose intolerance. The ability to digest lactose could be restored with proper treatment. However, secondary lactose intolerance may also be genetic - like in congenital or developmental lactose intolerance, in which babies are born lacking lactase.

Tests can be used to diagnose the condition. One such test is the hydrogen breath test, which measures the hydrogen gas in your breath and uses it as an indication of how well you digest lactose.

The common treatment approaches for lactose intolerance involve reducing or eliminating lactose completely or treating the other underlying causes like inflammatory bowel disease (IBD), bowel infections, bowel surgery, or injury.^2,3

Gluten intolerance

Gluten is a type of storage protein found in wheat, barley, and rye. It is associated with health conditions, like autoimmune celiac disease (CD) (wheat allergy) and non-celiac gluten sensitivity (NCGS). Non-immunological non-celiac gluten sensitivity (NCGS) has a worldwide prevalence of 0.5–13%. After ingesting gluten, patients with this condition may experience bloating, diarrhoea and constipation, stomach pain, headache, migraine, fatigue, abdominal pain, anxiety, brain fog, and depression.⁴

If a doctor has confirmed your diagnosis of gluten intolerance, you would need to follow a gluten-free diet.

Enteral histaminosis

Enteral histaminosis, also referred to as histamine intolerance, is a disorder associated with the impaired ability to process dietary histamine.⁵ Histamine is a biogenic amine (meaning that it is a compound made by a living thing that contains an amine group). It is formed from the amino acid histidine during a reaction catalysed by the enzyme L-histidine decarboxylase. Histamine can be found in many foods, which vary greatly in their histamine content. The following table shows the levels of histamine found in different foods:

Histamine intolerance varies from person to person. The following table illustrates the symptoms and diagnostic criteria of histamine intolerance:^6,7

Treating histamine intolerance starts by lowering histamine dietary intake through a three-step protocol.⁸

The first phase consists of a 4-6 week strict low histamine diet. The second phase allows the reintroduction of histamine-rich foods to determine the individual’s tolerance. Finally, in the third phase, a long-term diet is created for the individual depending on their histamine tolerance. 

FODMAPs intolerance

FODMAPs stand for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. They are short-chain carbohydrates (sugars) that the small intestine absorbs poorly. Some people experience digestive distress after eating them. Symptoms include bloating, gas, diarrhoea or constipation, and cramping. Research suggests that this specific group of carbohydrates may worsen the symptoms in individuals with functional gastrointestinal conditions like irritable bowel syndrome (IBS).

Two main mechanisms have been proposed to explain how FODMAPs might trigger symptoms. The first is the osmotic effect - as the FODMAPs are poorly absorbed short-chain carbohydrates, thus can draw water into the small intestine.⁹ Those findings were confirmed by studies of the output following a high FODMAP diet.^10,11

The rapidly fermentable FODMAPs cause increased gas production when they reach the colon due to their fast fermentation by the gut bacteria. This was confirmed to trigger symptoms of FODMAP intolerance via MRI scans.^10,11

To treat people with FODMAP intolerance, doctors usually suggest following a low FODMAP diet. It is a three-phase diet implemented by a dietitian. Similarly to the plan used to manage histamine intolerance, the plan starts with the short-term restriction of FODMAP-containing food for two to eight weeks, followed by the reintroduction of FODMAP-containing food phase to identify triggers, and in the last long-term maintenance phase, patients will only avoid FODMAPs identified as problematic in the reintroduction phase.

The gut microbiome: an innovative food intolerance treatment approach

Our gut is home to a vast and diverse community of microorganisms. This ecosystem, known as the gut microbiome, plays a crucial role in our health. The National Institute of Health (NIH) Human Microbiome Project identified more than 1014 microorganisms residing in our intestines, each with an important function.

The composition of this microorganism community is not random. It varies throughout the gut and is heavily influenced by what we eat.^12,13 Over time, humans and these microorganisms have developed a symbiotic relationship. We provide them with prebiotic fibres (found in fruits and vegetables), which they ferment to produce short-chain fatty acids (SCFAs).

These SCFAs, in turn, help regulate our immune system.¹⁴ However, modern practices, like the overuse of antibiotics, and high-sugar and low-fat diets disrupt this delicate balance. This disruption is linked to various health problems.¹⁵

A systematic review published in Critical Reviews in Food Science and Nutrition assessed fifteen randomised double-blind studies to determine the effects of probiotics on lactose intolerance results found a positive therapeutic relationship between probiotics and lactose intolerance.¹⁶ Another randomised, double-blind, cross-over study published in Nutrients studied the effects of Bifidobacterium longum and Lactobacillus rhamnosus bacteria on the gut microbiota in patients with lactose intolerance.

The study supported the correlation between the probiotic and vitamin B6 treatment and reduced symptoms via the positive modulation of gut microbial composition.¹⁷ Researchers have identified a strategy to combat gluten intolerance through exogenous enzymes as a supplement allowing them to to break down gluten effectively.¹⁸

Another crucial role of the gut microbiome is maintaining the integrity of the intestinal barrier. When healthy, the intestinal barrier acts as a gatekeeper and protects our gut. In contrast, a compromised barrier may allow partially digested food components and bacterial products to leak into the bloodstream, activating the immune system and leading to the symptoms associated with food intolerance.¹⁹

Summary

In conclusion, the gut microbiome plays a significant role in food intolerance. This crucial microorganism community is changeable depending on factors including diet, stress, and environmental factors. Understanding the gut-microbiome-food intolerance axis opens doors for potential therapeutic interventions in the future.