10 Food Myths Put to the Test

1. Eating chocolate gives you pimples

Not so, says Dr Pam Brown, fellow of the Australasian College of Dermatologists. "There is no good data that support that theory, although it used to be in a lot of dermatology textbooks. It's a myth that has a long history; it was originally touted in the early 1930s. There were a couple of studies in the 1960s and '70s, but these studies were poorly designed and not well done.

We do know that food is possibly one of a great number of factors, including genetics and the structure of the diet, that lead to acne." There is, she says, some evidence that high glycemic load may affect the body's production of the hormone androgen, "and androgen is one of the things that, in a genetically susceptible person, drives the development of acne lesions. But chocolate itself hasn't been implicated."

2. An apple a day keeps the doctor away

"It's obviously not literally true," says Dr Ronald McCoy, senior medical educator and spokesperson for the Royal Australian College of General Practitioners, "but as a metaphor there's a lot of truth to it. It recognizes that fruit is an important part of the diet and needs to be included on a regular basis. But you notice it's 'an' apple, not 50 apples a day. It should be part of a balanced diet. And while apples are full of antioxidants, it doesn't have to be an apple; it's symbolic of fruit in general. So the gist of it is quite sound: moderate amounts of fruit as part of a balanced diet are an important factor in improving longevity."

3. Drinking cranberry juice can cure a urinary tract infection

"There is no evidence that cranberry juice or cranberry tablets will treat an established infection," says Dr David Malouf, president of the Urological Society of Australia and New Zealand. "A bladder infection should be managed with antibiotics prescribed by a doctor. An untreated infection can spread to the kidneys (called pyelonephritis), which can make the patient very unwell.

"However, there is evidence that regular cranberry juice or cranberry tablets may reduce the risk of developing a urinary tract infection (UTI) in the first place. The current thinking is that cranberry stops the bacteria – the germs that cause UTIs – from adhering to the bladder wall. It's one of several strategies a patient with recurrent UTIs might try to reduce the chance of re-infection."

4. Fish is brain food

This one's true. Eating fish has numerous health benefits, including a significant decrease in the risk of heart disease and stroke (because fish oils are rich in the unsaturated fatty acids known as omega-3s, and these decrease the stickiness of blood platelets and increase the flexibility of red blood cells). But it also has specific benefits for the brain, especially in later life, and again it's a result of those omega-3s.

A study from Rush University Medical Center in Chicago found that eating fish once a week led to a 60% drop in cognitive decline in older people, and significantly reduced the risk of developing conditions such as Alzheimer's. In her book 100 Simple Things You Can Do to Prevent Alzheimer's, Jean Carper quotes Dr Emiliano Albanese, who studied the diets of 15,000 people aged over 65 from seven countries: "The fact is, the more fish you eat, the less likely you are to get dementia." Those who ate it a few times a week had 20% less chance of dementia, and those who ate it every day reduced their risk by 40%.

5. Avoid milk, especially when you have a cold, because it makes mucus

This incredibly persistent belief is completely false, says Dr McCoy. "Milk is a really important source of calcium, particularly in children, so it's important to allay this fear totally. There is good, scientific evidence – it's been looked at so closely – and the evidence is incontrovertible: there is absolutely no relationship between the two. But people don't believe that. The fact that they have a virus, which is causing them to produce mucus, seems irrelevant! People have fears around health and it takes a big grown-up to face their fears and say, 'Well, the evidence shows there's no connection'. If people persist in believing otherwise, they're being irrational."

There is, he adds, "no connection between lactose intolerance, which is about bloating and diarrhea, and mucus production. (It's also quite uncommon for people raised on a Western diet to be completely lactose-intolerant.) People need the courage not to pander to those fears." This means saying to well-intentioned relatives and friends who push the myth, No, that's not true. "Look at it this way, if you're a parent, do you want to pander to a fear or have a child who develops osteoporosis later in life? It's a no-brainer."

6. Eating carrots improves your eyesight

This one has some truth in it. Eating carrots won't prevent or fix problems such as being short- or long-sighted, but eating even a single carrot every few days can be enough to prevent certain kinds of night-blindness. That's because some night-blindness, a condition in which the eye cannot adjust to dim light, is caused by a lack of vitamin A, and carrots are rich in betacarotene, which the body converts into vitamin A.

7. Spicy food gives you ulcers

"It does not," says Professor Bolin. "There was a wonderful study done some years ago, feeding an extraordinary amount of chilli to people and that didn't cause any problems. What spices do is disturb a potential irritable bowel. So if they do give you pain, you're likely to say, 'Oh, that's ulcer pain', but it's really not. It's pain from your bowel.

"We now know that a bacteria called Helicobacter pylori is the cause of almost all ulcers, except those caused by arthritis medication and aspirin. You wouldn't know if you had Helicobacter. Most people who do – that we see – have had it since they were a child or a teenager. We presume it's related to nutrition and water supply, because it's extraordinarily common in places such as Asia, but is disappearing in places like Australia."

8. Feed a cold, starve a fever

"This is absolutely wrong," says Dr McCoy. "People with a fever need their nutrition. They can find it harder to eat, but it's important they have small amounts regularly. They need to eat what they can tolerate. When people are sick, their nutritional needs increase; the metabolic rate goes up. People with fevers can lose weight very, very quickly. I once saw a patient with fever who lost 17 pounds in four days, and it wasn't fluid loss – he was on a drip – it was probably muscle wasting. So if you have someone with a fever, give them fever reducer and half an hour later when it has kicked in, that's the time to feed them. They'll probably be more able to eat then."

9. Eat yogurt to cure a yeast infection

"The jury's still out on this one," says gynecologist Dr Kristine Barnden. "The rationale is very plausible." Normally, "friendly" bacteria called lactobacilli in the vagina make the environment very acidic, which suppresses yeast organisms such as candida. But if something suppresses the lactobacilli, such as taking a course of antibiotics for an unrelated condition, the yeasts will flourish. "It's thought that eating yogurt that contains bacteria such as acidophilus, or even plain, ordinary yogurt, will restore the proper balance.

The trouble is there are no large, well-designed studies that prove yogurt works in this way, yet there are a few that showed no effect at all. We also hear a lot about probiotics (bacteria such as acidophilus that are consumed with a medicinal purpose in mind), but, says Dr Barnden, "all of the trials that have looked at this have shown a very strong placebo effect." In other words, it may only work because people believe it will work. "Still," she says, "there's no harm in eating yogurt."

What will cure thrush is over-the-counter antifungal medication, but if you're not sure it's thrush, or if it persists, "it's important to see a doctor".

10. Ginger taken in tea will cure an upset stomach

"There are lots of these herbal remedies about that have a reputation for being good, and I think sometimes it's because the problem that you're taking it for doesn't last too long. So, whatever you take, you're going to feel better the next day," says Professor Bolin. 

"There's no evidence that things like ginger will help. Peppermint will, particularly for reflux, and that can be taken as tea or as capsules containing peppermint." He makes the point that this pertains to the herb, not to peppermint candies.