What is lactose and what role does it play in the gut?

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You’ve probably heard the word lactose before.

It’s likely you have at least one friend who is lactose intolerant.

But you might not fully understand what lactose is and how it actually works in your body.

To help you out, Mamamia spoke to Dr Jane Bowen, a Research Dietitian/Scientist at the CSIRO Health and Biosecurity unit.

Dr Bowen explained that lactose is essentially an energy source – like carbohydrates, it’s processed in the body to give you energy. Lactose is a disaccharide, a sugar that’s made up of two units called glucose and galactose.

The problem with lactose is that not everyone is able to digest it easily.

“In order to be able to use it as a form of energy, it needs to be digested from that joined up combination of two units into single sugar units,” Dr Bowen explained.

Lactose is digested by using a very specific enzyme called the lactase enzyme, which lines the inside of your small intestine.

“So imagine the small intestine is a small pipe, like a hose, and in the inside there are a whole range of different things,” Dr Bowen explained. “One of the things that lines the inside of it are the enzymes that digest food. Each enzyme digests a particular thing and the lactase enzyme digests lactose.”

symptoms of lactose intolerance
Image: Getty.

"It's common in children to have that enzyme there, but as people get older, that lactase enzyme is no longer produced or is produced in smaller and smaller amounts."

That's when people begin to experience difficulty digesting lactose and they might experience some uncomfortable symptoms.

"If you can't digest lactose then it can enter the bowel, where there's bacteria. And those bacteria can ferment that carbohydrate," said Dr Bowen.

"So that fermentation from the bugs in your lower gut produces gas, which can cause bloating, flatulence, abdominal pain and cramping."


However, not everyone will experience symptoms. Some people's guts may have difficulty digesting lactose but it won't result in any noticeable symptoms.

"If you eat it and you don't experience any tummy pains or bloating, then that's fine," Dr Bowen added.

When people do encounter symptoms like bloating, gas and tummy pains after consuming dairy products, they might be experiencing lactose intolerance.

"The difference between not digesting the lactose and not tolerating it is when there is excessive gas that's produced, or excessive bloating, or excessive abdominal pain, that causes unpleasant symptoms.

"So that's when we say you're lactose intolerant - because you can't tolerate the consequence of the bacteria digesting that lactose. And that usually happens within 30 minutes to two hours of consuming the lactose."

Dr Bowen says it's important to get a proper diagnosis, even if you experience symptoms, because it could be something else that's causing them.

"Lots of people will think they're lactose intolerant but it's actually not caused by the lactose itself," she says. "It's caused by some other aspect of the milk or it might be a learned or anticipated response that you almost talk yourself into if you've had one quite unpleasant experience."

"For people who suspect they have a lactose intolerance, it's really valuable for them to get an accurate diagnosis. It may not be the lactose that's causing the problem, it could be something else. So you may continue to experience symptoms that you're not getting relief from."


Your GP or an Accredited Practising Dietitian will be able to help you figure out whether you actually have an intolerance and exactly how much lactose you can tolerate.

symptoms of lactose intolerance
Image: Getty.

"So working with your GP or an Accredited Practising Dietitian is a very useful thing to get to the bottom of your tummy troubles so you can still maintain a diet that's as healthy and varied as possible," Dr Bowen said.


"When you avoid dairy, you're missing a really good source of calcium and a good source protein."

Dr Bowen explained that being lactose intolerant doesn't necessarily mean you have to give up dairy completely.

"Your tolerance level can actually vary," she said. "So some people can cope with a small amount of yoghurt that might be mixed into a cake, but they couldn't drink a large milkshake in one hit."

How you consume dairy will impact how you tolerate it. If you eat it with other foods, it will pass through the gut more slowly, and therefore you will have a higher tolerance to it. For example, a milkshake as a snack would be harder to tolerate than a glass of milk that's eaten with a meal.

It's also important to remember that different dairy foods contain different amounts of lactose.

"So hard cheese tends to be very low in lactose and therefore more easily tolerated," Dr Bowen explained.

"Softer cheeses tend to be a little bit higher in lactose. Milk is quite high, but people will tolerate it a little better if they choose full fat milk. Because, again, that slows the rate that the milk goes through the gut."

You can find out more about lactose and how it works with your body at Dairy Australia's website.

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