Skip to: Main Navigation | Main Content

or try the A-Z Library


8 common food beliefs: fact or fiction?

by ABC Health and Wellbeing

Does milk cause mucus? Is it safe to salvage mouldy cheese? Can eating a lot of lollies give you diabetes? Here's what the science has to say on some common points of confusion surrounding the food we eat.


There's no denying what we eat can have a profound impact our health. But there's plenty of myths and misunderstandings about what's safe or healthy and what's not. Here's where the evidence lies on eight popular beliefs.

1. Eating burnt toast gives you cancer

Verdict: Maybe. Some chemicals in burnt toast have been linked to cancer.

No-one has ever investigated whether people who eat a lot of burnt toast have higher cancer rates. And lab rats have never been fed burnt toast to see whether it causes tumours, says Dr Paul Brent, the chief scientist of Food Standards Australia and New Zealand (FSANZ).

But there are chemicals in burnt toast that have been linked with cancers in both animals and humans. So it's certainly not the healthiest snack and is probably better avoided.

Brent's advice? Don't be tempted to eat charred toast. And while it might feel wasteful, don't try to salvage it by scraping the burnt part either. You're better off just trying again.

More info: Can eating burnt toast give you cancer?

2. Drinking milk makes mucus worse

Verdict: No, it might feel like it, but milk does not increase mucus production.

While many people swear milk produces more mucus – making their nose run and their throat clag up – the effect can't be explained by science, says allergy specialist Dr Ray Mullins.

This doesn't mean people don't experience the sensation, says Mullins, but rather that there is no actual increase in mucus production.

He puts the sensation down to the texture and viscosity of milk, and notes that most people do not report similar effects with other dairy products such as cheese.

While many people call the mucus-milk phenomena an allergy, it's not, he says. And he warns against elimination diets as they can have serious nutritional consequences. And in any case, the results, in his experience, have almost always been disappointing.

More info: Does milk make mucus worse?

3. Eating a lot of sugar gives you diabetes

Verdict: Maybe, but most experts say there's nothing special about sugar. Over-eating any food can make you fat, which can cause diabetes.

It's true that diabetes is a disease where there's too much glucose – a type of sugar – in your blood. But just because you have high blood sugar doesn't mean eating a lot of sugar is what got you there, says Ian Caterson, Boden Professor of Human Nutrition at the University of Sydney.

In fact, the notion there's a direct link between eating sugar and developing diabetes is a myth, Caterson says.

However, eating too many sugary foods can lead to weight gain, a key trigger for the most common form of diabetes: type 2. But so can eating too much of many other unhealthy foods, not just those high in sugar.

"It is more being overweight – particularly around the waist – that is linked with type 2 diabetes than any particular food you eat," he says.

More info: Can eating a lot of sugar give you diabetes?

4. Swallowing chewing gum clogs up your gut

Verdict: It's pretty rare, but it can happen.

Chewing gum isn't intended to be swallowed, but if it is, the gum base remains largely undigested. In most people, this doesn't cause any problems. It passes through the intestines and out into the toilet.

But If you swallow a lot of gum over a long period of time, you can develop a non-digestible lump called a bezoar that sometimes doesn't pass out of your body: "If it starts off as a small lump and you keep on swallowing, the gum can stick and it can grow like a snowball," says Dr Nitin Gupta, a paediatric gastroenterologist at Sydney's Children's Hospital.

That's what happened to one 18-year-old woman with tummy pains whose case made it into a medical journal. She had been swallowing at least five pieces of gum a day for several years and her stomach was jam packed with a gum ball.

It's more likely (but still rare) for kids to have problems after swallowing gum because of their tendency to swallow other small objects like say, coins, which combine with the gum to form an even bigger bezoar. And their intestines are narrower than adults, so a bezoar is more likely to get stuck.

To be on the safe side, try not to swallow gum.

More info: Can swallowing chewing gum really clog up your gut?

5. Eating soy foods increases your risk of breast cancer

Verdict: Not likely. Research is limited but there's more evidence soy is helpful to health than harmful.

Soy contains large amounts of phyto-oestrogens (or isoflavones), plant chemicals that mimic the hormone oestrogen, although on a much weaker scale.

Since one risk factor for breast cancer is high levels of oestrogen, concerns were raised when research found phyto-oestrogens increased the risk of breast cancer in rats. But no studies on humans have found that eating soy as part of a healthy diet can be harmful. In fact, research on Asian women has found soy may actually help prevent breast cancer.

Dietitan and breast cancer researcher Dr Kellie Bilinski says the rats in the studies were given huge doses that we'd never actually consume and differences in metabolism mean the results can't be directly extrapolated to humans anyway.

Our national dietary guidelines still recommend we eat one to two serves of soy a day as part of a healthy diet.

The bottom line is that soy foods don't just contain isoflavones, they also contain hundreds of other beneficial ingredients like protein, fibre, iron, omega-3 fatty acids and calcium.

If you're eating a fair amount of these foods, then you're probably putting less chips and pies in your mouth – and that's going to be good for your health.

More info: Do soy foods increase your risk of cancer?

6. Yoghurt can cure thrush

Verdict: No, neither yoghurts containing live bacteria, nor isolated supplements of the 'good' bacteria found in these yoghurts seems to help.

Thrush occurs when there's an overgrowth of yeast in the vagina. For years the idea yoghurt containing live or active cultures could prevent or cure thrush has been popular. The idea is that 'good bacteria' known as Lactobacillus in the yoghurt can fight off the yeast. You can use the yoghurt topically, inserting it into the vagina using a tampon, or you can boost your Lactobacillus more broadly in the body by eating the yoghurt.

But GP and academic Marie Pirotta spent five years researching vaginal thrush and says neither yoghurt nor supplements of Lactobacillus help prevent or cure thrush.

If you get thrush regularly – especially after antibiotics – get a treatment from your chemist and use it at the first sign of symptoms. If these symptoms continue after treatment, see your GP.

More info: Will yoghurt cure thrush?

7. You can cut mould off cheese but not bread

Verdict: Yes, it's generally safe to eat cheese after mould's been cut off but don't try to save mouldy bread or most other mouldy foods.

From a mould perspective, hard cheese is one of the few foods where what you see is what you get, says Dr Ailsa Hocking, of CSIRO Food and Nutritional Sciences.

The low moisture content of hard cheese and its dense structure mean there's unlikely to be mould beyond what the eye can see. In other words, mould will usually survive only on the surface, rather than spreading invisibly into the cheese. So it should be safe to cut around the affected area and eat the rest of the block.

But in porous foods (like bread and cake) and foods with a high moisture content (like soft fruit and veg and soft cheeses), it's much more feasible mould is growing beyond the areas you can see, and this can make you sick.

So when these foods are mouldy, you're better off throwing the lot away.

More info: If you cut mould off food, is it then safe to eat?

8. Eating carrots improves your night vision

Verdict: Maybe. Carrots will help only if you're lacking vitamin A in your diet (which most Australians aren't).

A diet deficient in vitamin A can lead to night blindness and other eye problems. Since carrots (along with broccoli, sweet potatoes, pumpkin and dark-green leafy vegetables) contain a substance that is converted to vitamin A in the body, eating these vegetables can help if you have poor night vision caused by a dietary deficiency in vitamin A. You'll also need to be getting enough iron and zinc.

But vitamin A deficiency is rare in Australia. No amount of carrots will improve your eyesight if you already have a well balanced diet, says Professor Algis Vingrys, from the University of Melbourne's Department of Optometry and Vision Services.

Also poor night vision can have other causes, such as ageing, and carrots or other food sources of vitamin A won't help that.

More info: Can eating carrots improve your eyesight?

Published 15/07/2014