Lactose and Gluten Intolerance: Are they real?


It has become common practice to blame lactose (the main sugar or disaccharide in dairy) and gluten (a selection of proteins in grains like wheat) for IBS symptoms.

This practice is then ‘verified’ by mild symptom improvement when these foods are taken out. It’s not that simple, and these two components of foods, that lets face it make up core components of many peoples diet, may be getting a bum wrap. Not to mention cutting them out completely, and unnecessarily can limit a persons ability to absorb key nutrients, like (Calcium) and essential fibre.

So let’s tackle the key points. What is considered an intolerance or allergy. How it arises, how to test for the intolerance and could it be anything else? Finally what can be done about it.

What is an intolerance and an allergy?

According to FSANZ (Food Standards Australia New Zealand).

Food Intolerances: a reaction to food, that causes
  • rashes and swelling of the skin, asthma, and stuffy or runny nose
  • irritable bowel symptoms, colic, bloating, and diarrhea
  • migraines, headaches, lethargy, and irritability.

These reactions are NOT allergic reactions. Once you read through this post you’ll see that lactose is correctly labelled a food intolerance. However if you produce lactose there is nothing wrong with having dairy in your diet.

Food Allergies: can be fatal, involve anaphylaxis where the persons immune system reacts to the food.

Common foods that can cause an allergic reaction include:


Dairy first! What is lactose?

It is a disaccharide meaning it is a sugar made up of 2 units. 1 galactose, bound to one glucose unit. It is found in milk from mammals, and in varying levels, the products made from milk. When we consume dairy, the lactose travels to our small intestine, where the enzyme lactase should be produced, in reaction to the presence of lactose. If you want more info check out this useful Kahn academy video.

A simple picture showing enzymes, breaking bonds between 2 units of sugar, represented as different shapes connected by a line

Lactase, the enzyme, specific to lactose, is considered a brush border enzyme as it is made by part of the villi, and they look like brushes (it’s a bit more complex than that, if you want more check out the linked Kahn Video). The lactase comes and snips the bond between galactose and glucose units. They are now just sachharides or mono-saccharides, meaning 1 unit. This means transporters specifically made for single glucose and galactose can absorb the single units into the blood stream. These single sugar units are then carted off to for use in many places (muscles, liver, brain). They are important in the production of energy and can also, if needed be made into other things.

So what is lactose intolerance?

When someone doesn’t produce enough lactase or any lactase, this causes lactose intolerance. When this happens, the disaccharide isn’t snipped into 2 units. The transporters cannot absorb the disaccharide, it’s too big and the wrong shape.

What does this mean?

As the disaccharide stays in it’s original form, it is considered osmotically active. In the small intestine it draws in water to the bowel, as well as the large intestine. This is the main cause of diarrhea in lactose intolerance.

The lactose disaccharide then travels all the way to the large intestine, drawing water into the bowel as it goes (this is quite a long way). Where our guts natural bacteria, use it for food. The gut bacteria eat the 2 unit sugar and produce waste products. These waste products are: hydrogen, methane, and short chain fatty acids which can have other other effects on the intestine.

The gasses cause bloating and flatulence. While the short chain fatty acids can cause changes in the gut motility. This means it changes how the smooth muscle of the intestine acts. Our intestines are made of smooth muscle which contracts subconsciously, we have no control over it. However it can be stimulated by other things, for instance caffeine. This is called peristalsis.


I tried to write an explanation but really kahn academy explains it better, and visually! In this video, imagine the area of higher solutes is the small intestine - where large units of lactose sit in the small intestine, not being able to cross to the blood stream. While the blood is the area with less large units, the solutes in the blood small enough to cross are water molecules. 

What else can cause osmotic diarrhea, bloating and gas?

A few different things.

Causes discomfort but not a disease

  • Other carbohydrates the body cannot digest (known as FODMAPs)

Cause discomfort and considered a disease

  • Un-diagnosed coeliac disease (more on this on our gluten intolerance blog post)
  • Endometriosis
  • Inflammatory Bowel Disease (IBD) like Crohns Disease & Ulcerative Colitis.
Image showing a visual of a bowel with normal lactose digestion as well as abnormal digestion where the 2 unit disaccharide isn't cut in half and there is water drawn into the bowel and fermentation. Showing how lactose intolerance works

What tests can be done to confirm lactose intolerance?

The gold standard test for lactose intolerance is a trial low lactose diet then reintroduction. A breath test can be done for lactose malabsorption. However the breath test only tests for malabsorption it cannot test for lactose intolerance. The breath test is also in larger amounts to what someone would consume in one sitting, as such it can be misleading. A person could potentially tolerate lactose at lower levels but test positive for a breath test.

Many people find a low lactose diet is a quick and effective way to find symptom relief. If not then a  low FODMAP diet should be considered under the supervision of a dietitian. The dietitian will also cover all ground, and make sure there isn’t a differential diagnosis that requires more focus (such as coeliac disease and IBD).

Take care!

Depending on your life stage, suddenly eating a lower lactose diet can have a knock on effect on long term health outcomes. Lactose is usually a key component to high calcium containing foods. This is especially important for children, adolescents and post-menopausal women and older adults. Potentially also fertility and if you get bad PMS.

If a low lactose diet is the only way to control symptoms, focus on other high calcium containing foods, as well as a calcium supplement. Lactose free milk is also a good option.

Is there a quick fix?

Over the counter lactase preparations can be bought and consumed around the same time as lactose. These may work for some people, may not for others. Trialing these lactase preparations, controlled environment (home, near a loo!) is the best option.

It’s also important to note lactose intolerance can change over time, so it’s important for people to re-challenge themselves on a regular basis (say every 6 months). This way you may be pleasantly surprised, that milky flat white or creamy bree may be back on the cards.

Lactose in Summary

So yes lactose intolerance is very much real, and does affect a proportion of the population . It can depend on ethnicity, and family history. However it is important to trial a low lactose diet, exploring other options (coeliac disease) and potentially a breath test before deciding dairy is the cause of all issues. As it may be other FODMAPs as discussed or even IBD. Check out the Monash University website for more information on FODMAPs. Contact your GP or an Accredited Practicing Dietitian for help with food intolerances.


to be continued in our next blog post! Is Gluten naughty or nice. Is coeliac disease an intolerance or an allergy and is non-coeliac gluten sensitivity real?

Happiness is the smell of freshly baked bread

Share on facebook
Share on google
Share on twitter
Share on linkedin
Share This Article
Share on facebook
Share on google
Share on twitter
Share on linkedin
Don’t Stop Here

More To Explore

Scroll to Top