Lactose is a naturally occurring sugar found in animal breastmilk, for example, cow, goat and human milk. Per 100 ml, breastmilk has about 7 mg of lactose. Most infant formulas also have about 7 mg, though they don t come packaged with compounds to help digest it. Cow milk has around 5 mg.
It appears that lactose may perform a special function in early childhood development, which is why production of lactase (the enzyme that digests lactose) drops off as our bodies begin to cease growing rapidly, settling down by around 4 years of age. So, while our ability to digest lactose reduces with age, lactose nonetheless performs a function in human nutrition.
What is lactose intolerance?
Lactase is produced in the small cells that line the intestinal canal. Hence, any condition that affects the health and integrity of these cells can impair lactase production.
Food entering the intestinal tract is broken down into smaller units that can then pass into the inner workings of the body for use. To digest food, we need a huge array of enzymes and factors; occasionally some may be low or even missing, and lactase is a good example. When lactase is low (or in rare extreme cases, not present), this impedes the body's ability to break lactose into smaller sugars (glucose and galactose). The undigested lactose continues to pass along the intestinal tract and as it progresses, bacteria works on it, causing a fermentation process that result in gas forming and water being drawn into the area. It is this process that leads to some of the symptoms of lactose intolerance (LI), including bloating, flatulence, diarrhoea and tummy pains.
Our production of lactase drops off markedly over our first four years. However, in some cultures where pastoral activity such as dairy farming has a long history, there appears to have been a genetic adaption over time that inhibits the slowing of lactase production. Interestingly, lactose intolerance genes are not dominant genes.
Even those with mild lactose intolerance can, it seems, up-regulate the enzymes involved in lactose digestion via continual small exposure to lactose. Basically, over time we can gain a tolerance to a certain level of lactose. Having said this, like so many things in nutrition, you can still have lactose intolerance and not show any symptoms.
Types of lactose intolerance
Genetic lactose deficiency in newborns is quite rare and in such cases urgent medical intervention is necessary. Most cases of lactose intolerance are due to a genetic disposition to low lactose and this is generally influenced by ethnic background.
Lactose intolerance can also be a secondary occurrence to gastric upsets, a bout of gastroenteritis or parasitic infection. While this is often a temporary issue in little ones, the younger the baby the longer they are likely to take to recover (up to eight weeks). In babies, lactose intolerance can lead to runny (more than normal), frothy stools, irritability and excessive wind. Keep in mind also that anyone suffering from conditions that affect the intestinal tract, for example coeliac disease, may also experience greater rates of lactose intolerance. Iron deficiency also appears to interfere with lactose digestion and absorption.
There appears to be an interesting phenomenon of lactose overload , which can mimic lactose intolerance in babies. Nursing mothers, who have an overly abundant supply of milk, can find the baby experiences symptoms similar to lactose intolerance. For more on this, visit the Australian Breastfeeding Association website
Who is at risk?
Generally those most affected are from cultures that haven t had a great deal of exposure to pastoral practices such as dairy farming.
Rates of LI:
- Indigenous Australians – about 70%
- Asians 93%
- Greeks about 50%
- Middle Eastern cultures around 40%
- Those whose family history originates in Northern Europe around 5-10%
Don t confuse lactose intolerance with cow milk protein allergy (CMP)
CMP involves the immune system, which reacts to protein molecules that have passed into the bloodstream. It is quite different from lactose intolerance, generally more severe, appears affected by the maternal diet, has a familial factor and can interfere more with the diet.
Being lactose intolerant doesn t mean you will never be able to cope with lactose-containing foods again. In fact, in many cases removing lactose altogether is not helpful, as it can reduce your production of the enzyme used to digest lactose. Some people can tolerate a certain amount of lactose before they get into any problems. For example, by using low-lactose foods such as yoghurt and cheddar cheese as a source of calcium, the intolerance can be managed or in some cases be outgrown over time.
Chat with a suitably qualified healthcare professional to help you find the right level of lactose-containing foods for you or your child.
The Australasian Society of Clinical Immunology and Allergy
This information has been provided by Leanne Cooper Director of Cadence Health and Food Coaching Courses, Leanne is a registered nutritionist and mother of two very active boys.
This fact sheet may be reproduced in whole or in part for education and non-profit purposes with acknowledgement of the source. It may not be reproduced for commercial use or sale.
The information presented is not intended to replace medical advice.
Updated November 28, 2014
Last Published* December, 2022
*Please note that the published date may not be the same as the date that the content was created and that information above may have changed since.