Lactose Intolerance (also known as Lactose Malabsorption)

Which FODMAP is involved?


Lactose is a disaccharide comprising one molecule of glucose and one molecule of galactose. It has the chemical formula C12H22O11 and makes up anywhere between 2-8% of milk (by weight). The word lactose literally means “milk sugar;” this is appropriate, as it is found only in dairy-based products. Not all dairy products contain large amounts of lactose, however; some processing methods reduce or even eliminate its presence in foods – including cheesemaking, fermentation and enzymatic reactions.

The mechanism behind lactose intolerance/malabsorption

How should your body process lactose?

The villi in the duodenum of the small intestines of mammalian infants, as well as some children and adults, secrete the enzyme lactase (B-D-galactosidase); this cleaves the glycosidic bond that connects lactose together, splitting it into its two sub-units, glucose and galactose.

What happens in lactose malabsorbers?

The condition by which lactase production is reduced or nonexistent is called lactase deficiency. There are two main causes of lactase deficiency, genetic and environmental.

Many people now retain the ability to produce lactase into adulthood, this is thought to be a mutation of the MCM6 gene, which controls the whether the LCT gene for lactase production is switched on or off. Some people, however, do not continue to produce lactase – these people are typically from areas of South-East Asia and parts of Africa, or of Jewish or Mexican heritage, hinting at the strong genetic ties to lactose tolerance.

Another form is congenital lactase deficiency (CLD), in which the lactase production is reduced from birth. CLD was especially dangerous in the past, as an infant’s reliance on breast milk, without the option to supplement with formula, meant that they would be severely malnourished and often would not survive.

Not all people cease to produce lactase due to their genetics; in some cases, injury or prolonged insult to the gut from the environment will damage the villi such that they can no longer produce the enzyme. An example of this group are individuals with untreated Coeliac Disease (CD), who commonly become lactose intolerant as their condition goes untreated. It is possible that this form of lactase deficiency could be reversible, if the insult is removed however this is not guaranteed and it can take a long time for the required healing to occur.

In individuals with lactase deficiency, lactose (once consumed) will continue through the small intestine undigested and, therefore, be unavailable for absorption into the blood stream. The malabsorbed lactose then passes through the small intestine and into the colon, where it feeds the resident gut flora, resulting in the production, of hydrogencarbon dioxide and methane gas as well as short chain fatty acids and increased water retention.

What are the symptoms of lactose malabsorption?

The short list:

  • Altered bowel function/movements
  • Bloating
  • Cramps
  • Fatigue
  • Flatulence
  • Stomach/abdominal pain
  • Nausea
  • Peristaltic sound
  • Vomiting (if +++ amounts are consumed)

How is lactose malabsorption diagnosed?

There are two main methods to test for lactose malabsorption, the breath test and an elimination diet.

Hydrogen/methane breath test

Breath tests are non-invasive and simple ways to investigate whether a certain carbohydrate is being malabsorbed. The subject must follow a restricted diet before the exam (check with your testing centre).

A baseline reading of both gases is taken before the subject drinks a concentrated solution containing 50 g of lactose. After waiting for thirty minutes, the subject will then proceed to exhale into the collection bag at specific intervals, until hydrogen gas production either increases by 20 ppm, or 3 hours has passed (whichever comes first). An increase in hydrogen by 20 ppm is considered a positive diagnosis.

Elimination diet

Either individually or as part of the entire low FODMAP elimination diet, as per your dietitian’s discretion, lactose will be removed from you diet for a set period of time before being reintroduced in increasing amounts to test for tolerance.

Elimination diets are good for those who either don’t have access to the breath test or for those who feel that they still might have an issue with dairy, regardless of the breath test result. If you are part of the latter group, speak to your health practitioner, as other components of dairy can cause similar symptoms as lactose intolerance (see differential diagnoses bellow).

How do you manage lactose malabsorption?

Similar to fructose malabsorption, the symptoms associated with lactose malabsorption stem from the body’s inability to digest and thus absorb the lactose that is consumed. The amount of lactose required to trigger symptoms varies from person to person – some people can’t tolerate any at all but some can still put a little milk in their coffee, they just can’t drink a full glass.

To prevent the symptoms mentioned above, you will need to monitor your intake of lactose.

What do you need to avoid?

To control the symptoms associated with lactose intolerance, you must avoid consuming lactose above your tolerance threshold. For some, this might mean that a drop of milk in their cup of tea is safe but a glass of milk is not, for others, they must stay away from even the smallest amounts.

In general, foods that should be avoided are:

  • Cow/goat/sheep milk
  • Cream (full fat and light)
  • Buttermilk
  • Custard
  • Large amounts of chocolate
  • Certain cheeses (ricotta cheese, cottage cheese, cream cheese etc)
  • Ice cream
  • Some yoghurts

Safer, low lactose options include:

  • Lactose free/dairy free milk
  • Lactose free/dairy free cream
  • Lactose free/dairy free ice cream
  • Butter or ghee
  • Custard made with lactose free/dairy free products
  • Dark or dairy free chocolate
  • Hard or aged cheeses (cheddar, Parmesan, Feta etc)

Strategies to deal with accidental or unavoidable lactose consumption

Sometimes, either by accident or intentionally, lactose may be consumed in amounts that your gut cannot digest. If this is the case, you could try one of the below options:

  • Take a lactase tablet asap – this contains the enzyme your body is deficient in, which should help to digest the lactose you just consumed.
  • Take activated charcoal, which helps to absorb gas (as well as certain poisons). If you choose activated charcoal, be careful about timing it around taking important medicines, such as the contraceptive pill.
  • Soothing teas – ginger and mint both have gut soothing properties and may help to relieve symptoms.
  • Long term, taking a probiotic supplement (whether that be in tablet or food form, such as lactofermented sauerkraut, kefir or kombucha) can help to improve gut health and rebalance the flora in your colon, leading to less severe reactions if a lactose overdose does occur.

Differential diagnoses…

Other FODMAP intolerances

  • Fructose/fructan malabsorption.
  • Sorbitol malabsorption.
  • Coeliac disease – often, untreated coeliac sufferers will be lactose intolerant as well, due to the damage to the epithelial lining of the small intestine, caused by their body’s autoimmune reaction to gluten. Often, once gluten has been eliminated from their diet and adequate time has passed to allow for the gut to recover, the lactose intolerance may improve, or even disappear. The longer a coeliac has been left undiagnosed and untreated, the more time is required for their gut to heal.

Dairy protein allergy or intolerance

  • If you switch to a lactose free dairy milk and still suffer from digestive distress, you might be sensitive to one of the dairy proteins, such as casein or whey, rather than, or in addition to, the carbohydrate lactose. In this case, you must stay dairy free, rather than simply lactose free, to alleviate symptoms.
  • People can also have allergies to dairy proteins – if you notice reactions such as a rash, itchy skin or mouth, any swelling or difficulties breathing, please discontinue dairy consumption and visit your doctor as soon as possible for assessment.

Check out the FODMAP friendly food list and online resources pages for more information.