You are what you eat: biting into seven common food myths.

Seven common food myths that we’re debunking.

Your mother has warned you the sniff test won’t tell you if leftovers are off. Your girlfriend spends hours trying to convince you that she craves chocolate because her body needs it. And the office ‘health nut‘ has told you your morning cuppa is going to dehydrate you. But are any of these people speaking the truth?

There’s no shortage of myths and misunderstandings about what’s safe or healthy when it comes to what we put into our mouths. So we’re taking a closer look at seven popular food beliefs to see where the evidence lies.

1. You can smell when food is off

Verdict: Your nose doesn’t necessarily know when food is off.

It’s the end of a long day and you’ve gone from hungry to hangry. In desperation you reach into the back of the fridge and pull out a bowl of leftovers. You lift the lid and give it a good sniff to see if it’s still edible.

But trusting your nose is not going to save you from a bout of gastro (or worse), says Lydia Buchtmann from the Food Safety Information Council.

“A lot of people rely on the sniff test, [but] that means nothing whatsoever,” says Buchtmann.

According to Food Standards Australia New Zealand, food poisoning bacteria don’t change the appearance, smell or taste of food. (Bacteria known to cause food poisoning include Salmonella, Campylobacter jejuni, Staphylococcus aureus, strains of E. coli and Listeria monocytogenes. For more see An A-Z of common types of food poisoning.)

When a plate of leftovers starts to pong, it means spoilage bacteria have taken hold. These are different from bacteria that cause food poisoning.

Spoilage bacteria won’t usually make you sick, though food contaminated with them won’t be particularly pleasant to chow down on, and Buchtmann says it’s not a good idea to put it in your mouth.

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2. Drinking coffee makes you dehydrated

Verdict: If you drink coffee regularly and don’t drink too much it shouldn’t dehydrate you.

If you regularly enjoy a few cups of coffee or tea a day, then you can rest assured the moderate amount of caffeine your favourite drinks contain isn’t going to cause you to lose more fluid than you ingest, says Lisa Renn, accredited practising dietitian and spokesperson for the Dietitians Association of Australia.

Nor will your cuppa be any more likely to send you off to the loo than any other drink.

One of the reasons that drinks containing caffeine, such as coffee, tea, chocolate, cola drinks and energy drinks, have been given such a bad rap over the years is because caffeine is a diuretic when consumed in large doses (more than 500mg). Diuretics make your body produce more urine, so not only do they have you running to the toilet more often, they also cause you to lose sodium and water. When you lose too much sodium and water you become dehydrated, and this can have an effect on a range of bodily functions – from temperature control to absorption of food.

However, the amount of caffeine you get in a cuppa is unlikely to have these effects and it can actually contribute to your overall daily fluid intake.

“If you have to have more than four cups of coffee a day, you may see a diuretic effect from that, but if your intake is less, then from a dehydration view you’re going to be okay,” says Renn.

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3. Cravings are a sign your body needs certain foods

Verdict: Not likely. Most of us crave foods that we’re better off without.

If you think your cravings are a sign that your body needs certain nutrients, ask yourself how often you crave vegetables.

While there is a school of thought that people crave certain foods because they have a nutritional deficiency, scientists, focusing more on the psychology and neuroscience behind food cravings, have largely debunked this myth.

“Let’s face it, foods like cake, pizza, ice-cream, and chocolate aren’t really foods that any of us need to eat, they are just nice foods to have and they tend to be the ones that we crave,” says Associate Professor Eva Kemps from the School of Psychology at the University of Flinders in Adelaide.

There are some rare situations where nutritional deficiencies cause cravings; for instance sometimes people who are iron deficient will crave – and even eat – strange things such as ice, dirt or sand. This is known as pica and sometimes occurs in pregnant women or children.

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4. A vegetarian diet reduces your risk of cancer

Verdict: A plant-based diet can protect against some cancers, but that doesn’t mean you have to avoid all meat.

While a plant-based diet, which includes a wide variety of fruits, vegetables and wholegrains, has been shown to be protective against some cancers, there isn’t definitive evidence that avoiding all meat reduces your overall cancer risk, says Kathy Chapman, chair of Cancer Council Australia’s nutrition and physical activity committee.

Eating a lot of red meat – particularly processed meats, such as sausages, salami and bacon – is strongly associated with an increased risk of bowel cancer.

“Certainly our advice at the Cancer Council would be eating plenty of fruits and vegetables is what people should aim for,” Chapman says.

“If you want to follow a vegetarian diet you need to make sure it is a healthy one, but to lower cancer risk you don’t [necessarily need to] think about going totally meat free.”

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5. 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.

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6. 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.

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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.

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This post originally appeared on ABC News. You can read the original post here.

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