A Quick Guide To Understanding Food Intolerances

Latest Posts

Table of Contents

A Quick Guide To Understanding Food Intolerances

Date of Content:  November 23, 2023
Written by: Avanthika Nityanand
Reviewed by: Maarit Tiirikainen, PhD



What is Food Intolerance?

Food intolerance refers to difficulty in digesting certain foods, which can lead to uncomfortable gastrointestinal symptoms. Unlike food allergies, which involve the immune system and can be life-threatening, food intolerances generally result in less severe reactions that affect digestion.

Common symptoms of food intolerance include bloating, gas, diarrhea, constipation, cramping, and headaches. These symptoms often occur several hours after consuming the offending food. Some of the common intolerances are lactose (found in dairy), gluten (present in wheat and other grains), and histamine (in certain fermented foods). Unlike allergies, which start due to the consumption of tiny amounts of the allergen, food intolerances often depend on the quantity consumed and can vary over time.

Food Intolerances

How To Test For Food Intolerance?

Testing for food intolerance typically involves elimination diets and symptom tracking. An elimination diet requires removing suspected foods from the diet for a certain period, usually a few weeks, and then gradually reintroducing them while monitoring for symptoms. If symptoms reappear upon reintroducing a food, it might indicate an intolerance.

Additionally, specific medical tests can assist in identifying intolerances, such as lactose intolerance tests, breath tests for fructose malabsorption, and blood tests for celiac disease (which is an immune reaction to gluten but often grouped with food intolerances). However, it is essential to note that many commercial food intolerance tests that are available online lack scientific validation.

Can a Gastroenterologist Test for Food Intolerance?

A gastroenterologist can test for certain types of food intolerances. For example, they can administer breath tests to diagnose lactose or fructose intolerance and perform endoscopic procedures to diagnose conditions like celiac disease. However, for many food intolerances, there are no reliable clinical tests. So, a gastroenterologist may primarily focus on ruling out other gastrointestinal conditions and recommend dietary strategies for identifying intolerances.

What Happens if You Keep Eating Foods You are Intolerant to?

Consistently consuming food you are intolerant to can lead to chronic symptoms like diarrhea, constipation, and bloating. It can impact your overall quality of life. In some cases, it may also cause inflammation and irritation in the digestive system, potentially leading to more severe health issues, such as nutrient deficiencies or worsened gastrointestinal disorders.

What is The Difference Between Food Allergy and Food Intolerance?

Food allergies and food intolerances are often confused. But they are different. A food allergy triggers an immune system response that can affect multiple organs and be life-threatening (via anaphylaxis). In contrast, food intolerance is generally limited to digestive problems and is not life-threatening. Food allergies can start due to a tiny amount of the allergen and can develop at any age, whereas food intolerances often depend on the dose and may vary over time.

Can You Develop Food Intolerance Later in Life?

Yes, you can develop food intolerances later in life. It can be due to changes in your digestive system, such as a decrease in certain digestive enzymes (like lactase, which breaks down lactose). Age, changes in gut bacteria, and certain gastrointestinal diseases can also lead to the development of food intolerances.

Types Of Food Intolerances

Food intolerances come in various forms, each characterized by the inability to digest or react appropriately to specific food components. Unlike food allergies, which involve an immune response and can be severe or life-threatening, food intolerances typically cause uncomfortable digestive symptoms. Here are several common types:

  • Lactose Intolerance
  • Gluten Sensitivity
  • Hereditary Fructose Intolerance
  • Histamine Intolerance
  • FODMAP Intolerance
  • Additive Sensitivity
  • Amine Intolerance
  • Salicylate Sensitivity
  • Carbohydrate Intolerance
  • Alcohol Intolerance

Genetics Of Food Intolerances

Lactose Intolerance

Lactose intolerance is due to lactase deficiency.  Lactase is an enzyme needed to digest lactose, the sugar in milk and dairy products. Symptoms include bloating, gas, diarrhea, and abdominal pain.

The critical genetic aspect of lactose intolerance revolves around lactase persistence and non-persistence. Lactase persistence refers to the continued activity of the lactase enzyme into adulthood, allowing for the digestion of lactose.

Lactase non-persistence leads to lactose intolerance. The LCT gene encodes the lactase enzyme, and variations in this gene, particularly in the regulatory region upstream of the LCT gene, regulate lactase expression. The persistence or non-persistence trait depends on which alleles (gene variants) one inherits.

We have gone into much more detail about this gene and several other genes in our article, “Genetics of Lactose Intolerance.” You can read it here.

What Foods To Avoid if You Are Lactose Intolerant?

If you are lactose intolerant, it is essential to avoid foods containing lactose. It primarily includes dairy products like milk, cheese, yogurt, and ice cream. Some processed foods may also contain lactose as an additive, so reading labels is crucial. Lactase enzyme supplements are available to help digest lactose and may allow for small amounts of dairy in the diet.

Gluten Sensitivity

Non-celiac gluten sensitivity is different from celiac disease (an autoimmune disorder). Non-celiac gluten sensitivity causes bloating, abdominal discomfort, and fatigue due to consumption of gluten. Gluten is a protein found in wheat, barley, and rye.

While not as strongly genetically linked as in celiac disease, specific human leukocyte antigen (HLA) genes may play a role in gluten sensitivity. These genes are involved in immune system regulation and could contribute to our reaction to gluten. 

Hereditary Fructose Intolerance

Hereditary Fructose Intolerance (HFI) is a severe genetic disorder affecting the body’s ability to metabolize fructose, a sugar found in fruits, some vegetables, and honey. HFI follows an autosomal recessive pattern of inheritance.

In cases where both parents are carriers of a pathogenic ALDOB gene variant (heterozygous), there is a 25% chance that a child will have HFI, a 50% chance of being an asymptomatic carrier (having one pathogenic variant), and a 25% chance of not inheriting any pathogenic variant from the parents. It means that while each child has a risk of developing HFI, they also may be a carrier or completely unaffected genetically.

Histamine Intolerance

It occurs when the body cannot break down histamine, a compound in aged and fermented foods. It gives way to symptoms such as headaches, hives, digestive issues, and a runny nose.

The genetics of histamine intolerance are complex and involve multiple genes that influence the body’s ability to metabolize and respond to histamine. A few genes are responsible for producing enzymes involved in histamine metabolism.

For example, diamine oxidase (DAO), an enzyme synthesized in the intestines, helps metabolize histamine in foods. The AOC1 gene influences its production. Variations within the AOC1 gene can lead to differences in DAO production levels, affecting the efficiency of the enzyme in breaking down histamine.

FODMAP Intolerance

FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) are specific carbohydrates in some fruits, vegetables, grains, and dairy products. People with IBS (Irritable Bowel Syndrome) often find relief by following a low-FODMAP diet.

While no specific gene causes FODMAP intolerance, it may influence an individual’s susceptibility to IBS and similar gastrointestinal conditions, which affects how one tolerates FODMAPs. 

Twin and family studies have shown that IBS has a heritable component, with heritability estimates ranging from 0 to 57%. A notable study by the Mayo Clinic involving sequencing of the SCN5A gene in 584 IBS patients and 1,380 controls revealed that 2.2% of IBS patients had functionally harmful mutations in the SCN5A gene, which were absent in controls. This gene encodes the NaV1.5 ion channel crucial for gut function. The mutations, mainly resulting in loss of function and often linked to constipation-predominant IBS, highlight the genetic basis of IBS.

A severe case of IBS-C, with an SCN5A loss-of-function mutation, was effectively treated with mexiletine, which is a drug that restores NaV1.5 channel function. These findings suggest that both rare mutations and common variants could contribute to IBS. However, more large-scale genetic research on IBS is needed to uncover more genetic factors.

Alcohol Intolerance

Alcohol intolerance happens due to a genetic condition where the body cannot break down alcohol efficiently, leading to flushing, nausea, and rapid heartbeat.

Alcohol intolerance is predominantly influenced by genetic factors, particularly by variations in enzymes involved in alcohol breakdown. The key enzymes (entities that help speed up chemical reactions) are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH).

Genetic variations, especially in the ALDH2 gene, can lead to an inefficient breakdown of acetaldehyde, a toxic byproduct of alcohol metabolism. This inefficiency, associated with certain genetic variants,  is prevalent in East Asian populations and results in symptoms like flushing, nausea, and rapid heartbeat after alcohol consumption.

Can Genetic Testing Predict Food Intolerances?

Genetic testing for food intolerances involves analyzing specific genes that influence the body’s ability to process and tolerate certain foods. This type of testing can be helpful for conditions with a known genetic basis, such as lactose intolerance and alcohol intolerance. In the case of lactose intolerance, testing can identify variants in the LCT gene responsible for lactase enzyme production.

However, it is essential to note that the genetic component for many food intolerances is complex and not fully understood, making genetic testing less definitive. We should interpret the test results cautiously and in conjunction with clinical assessments and dietary trials.

Non-Genetic Factors Influencing Food Intolerance

Non-genetic factors play a significant role in the development and severity of food intolerances. These factors include:

  • Gut Microbiome: The composition of gut bacteria can influence the digestion and absorption of certain foods. Imbalances in the gut microbiota may exacerbate food intolerances.
  • Enzyme Deficiencies: Deficiencies in digestive enzymes, not caused by genetic factors, can lead to intolerances. For example, temporary lactase deficiency can occur due to a gastrointestinal infection.
  • Age: The body’s ability to digest certain foods can change due to age. It often leads to increased food intolerances in older adults.
  • Dietary Habits: Frequent consumption of certain foods can sometimes overwhelm the digestive system, leading to intolerance.
  • Gastrointestinal Diseases: Conditions like IBS can affect how the body processes certain foods, leading to intolerances.
  • Stress and Psychological Factors: Stress and emotional well-being can impact gut health and digestion, potentially contributing to food intolerances.
  • Food Processing and Additives: Certain food processing methods and additives can make foods difficult to digest or trigger intolerances.
  • Environmental Factors: Factors like pollution and exposure to toxins can impact gut health and digestion.


Customer Reviews

Christopher Devlin
Christopher Devlin
LifeDNA Customer
Read More
I am so impressed with this service. I have even discussed these recommendations with my health care providers and they are all impressed too! I can’t compare it with other services as I have only tried this but I recommend. Also I think I pulled my genetics in from ancestry too which was super convenient.
LifeDNA Customer
Read More
Great source of information I was looking for a platform to make use of my existing raw data from Ancestry. I’m glad I found LifeDNA. I originally took a DNA test to learn about my roots and it’s great to know that my DNA could also play a big role in my health, diet, and even my skin. Overall, all the reports are incredible.
Shiraz Dole
Shiraz Dole
LifeDNA Customer
Read More
It is crazy how I felt that I had a strong understanding of my bodies needs, but after having my DNA analyzed by the LifeDNA team, I realized that there was so much I still did not know.
Doc Sheila Lim
Doc Sheila Lim
LifeDNA Customer
Read More
I got some pretty useful insight that helped me with my diet.

*Understanding your genetics can offer valuable insights into your well-being, but it is not deterministic. Your traits can be influenced by the complex interplay involving nature, lifestyle, family history, and others.

Our reports have not been evaluated by the Food and Drug Administration. The contents on our website and our reports are for informational purposes only, and are not intended to diagnose any medical condition, replace the advice of a healthcare professional, or provide any medical advice, diagnosis, or treatment. Consult with a healthcare professional before making any major lifestyle changes or if you have any other concerns about your results. The testimonials featured may have used more than one LifeDNA or LifeDNA vendors’ product or reports.