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Common health stories: Fiction, fad or fact?

You’re happily enjoying what you’re eating when along comes a friend, or an email, stating your food is hazardous, or even – gulp – deadly! But what to believe? Senior nutritionist Rose Carr looks at the scientific evidence behind sensational food tales and delivers the truth of the matter.

Debbie, Tauranga

It’s easy to find websites which tell us if we keep eating microwaved food our hormone production will change, the electrical impulses in our brains will short out (causing permanent brain damage), and the microwaves cause various forms of cancer. But there’s no research to back up any of these claims.

The US Department of Agriculture tells us: “Microwave energy uses a wavelength similar to television, radio waves, electric shavers and radar. It does not make food ‘radioactive’. Nuclear radiation and X-rays are at the other end of the spectrum and are a million times more powerful.” People are also concerned about plastic containers and plastic wrap in the microwave. On this score it does pay to be cautious: using non- microwave-safe containers or  wrap could cause chemicals to leach into your food, which is clearly not ideal.

Our advice: There’s no evidence or reason to say microwaved food is unsafe or unhealthy. Microwaves have been safely used in homes for around 30 years. When cooking, use glass, ceramic or plastic containers marked ‘microwave safe’. When using plastic wrap, cover containers loosely, don’t let wrap touch the food and only use when cooking for less than one minute.

Janet, Papakura

The concern with non-stick coatings is about perfluorooctanoic acid (PFOA) which is used to produce them. The Environmental Protection Agency in the US has requested companies work towards eliminating the use PFOA by 2015. Laboratory studies with animals have shown PFOA to be toxic and carcinogenic in high doses. However, the concern is exposure by factory workers producing these products, and emissions from factories into their local environment, rather than the pans being used at home.

John Reeve, toxicologist at the NZFSA, tells us that at high temperatures (usually way above those normal for cooking) the non-stick coating can break down on pans, releasing strongly irritant fumes, but not PFOA. “Usually, the pan has to be red hot for this to happen so normal cooking temperatures are fine and no breakdown will occur, but avoid the high temperatures.”

Our advice: Non-stick pans are fine to use as long as you follow the pan instructions: to avoid damaging the non-stick surface, don’t overheat, and avoid scratching the non-stick surface with metal utensils or abrasive cleaners.

Ray, Takapuna

Many readers have been sent an email like this, which sternly warns never to save half an onion to use later, as it will attract bacteria and make you sick. It also credits onions with saving people from flu epidemics and diseases, when cut onions were strewn around the house.

The New Zealand Food Safety Authority (NZFSA) tells us they have had lots of enquiries about this, too, and they confirm what most of us suspect when we read this: these claims are not true.

Any food can be contaminated with bacteria, and any food can be cross-contaminated with harmful bugs as well, which is why good kitchen hygiene and food handling are important. But there’s no evidence that onions (cut or otherwise) are any more of a problem than other vegetables.

Our advice: Relax, and if you only want to use half an onion, you can safely save the other half, wrapped, in the fridge, for a few days.

Harry, Dunedin

We’ve heard this, too. There’s a view that because we humans are the only ones to drink milk from other animals, it must be wrong – drinking milk from cows or goats can be likened to drinking milk from our cats or dogs. And because some people can’t digest milk, as they don’t have the lactase enzyme needed to do so, it must mean we are not designed to drink milk.

That’s like saying the French should not eat frogs’ legs or Chinese people should not eat chicken feet, because some people think that’s gross. Or that we are not designed to eat nuts as they will kill people who are allergic. It is flawed logic.

Our advice: Milk is a nutritious food and an important source of calcium in many New Zealanders’ diets. Enjoy.

Danielle, Wellington

Raw food advocates say cooking diminishes the nutritional value and ‘life force’ of food.

While it’s true some compounds in some foods are more potent raw – like the cancer-fighting compounds in broccoli, which are best absorbed when it’s eaten raw – and some vitamins, like vitamin C, are destroyed by heat and light, it’s also true some foods are just inedible raw, like potatoes and chickpeas. Many antioxidant compounds are more readily absorbed when the food is cooked, such as beta-carotene (in carrots) and lycopene (in tomatoes). Eating only raw foods would make it difficult to get enough of many important nutrients.

Our advice: Cooking can make food taste better, kill food-borne bacteria, and some foods become more nutritious, not less. Eat a variety of foods, both raw and cooked, for maximum nutrition.

Sue, Blenheim

Dieters are often told to eat more frequently to help balance blood glucose levels, control hunger and boost metabolism. Researchers have tested this in many ways over the years and don’t seem to be able to come up with consistent conclusions. There’s little evidence to suggest meal frequency is in any way associated with weight or health. It seems any effect of meal patterns on body weight is likely to be the result of energy intake – how much you’re eating overall – rather than anything else.

Our advice: If frequent smaller meals work for your lifestyle, then go for it – just make sure they are smaller meals. If this doesn’t suit you, stick with three meals a day.

Sarah, Mosgiel

Some stories about plastic water bottles say you shouldn’t re-use them, some say you shouldn’t freeze them or leave them sitting in your car. All of these things are said to cause the breakdown of plastic and the release of toxic chemicals into the water. Food safety expert Caroline Gunn says: “Research presented in 2001 looked at water bottles made out of a common plastic, PET. It stated four chemicals were detected in the water in re-used plastic bottles exposed to certain conditions, like sunlight, heat, storage and time. These chemicals included the carcinogen DEHA. Since then there has been much debunking of the original thesis; further research has found concentrations of the chemicals were the same in blank water samples that had not been in contact with PET.

When it comes to freezing water bottles, there’s an email attributed to Johns Hopkins University in the US that says dioxins are released into the plastic by freezing. This email – which has been going around for at least four years – did not come from the university. What the university does state on its website, is: “There are no dioxins in plastics… freezing actually works against the release of chemicals.”

Another concern is plastic baby bottles. These are usually made from a different plastic, poly-carbonate, which contains a chemical called bisphenol-A (BPA). The NZFSA says, based on an extensive range of studies, BPA is safe at the very low levels we’re exposed to. It doesn’t believe that using polycarbonate baby bottles is placing infants at any risk. But it is keeping a close watch on developments in case there’s any new data.

Our advice: If you like your water cold, popping it in the freezer won’t do any harm, and there’s no evidence leaving your water in the car will, either. As a precaution, we recommend not re-using a plastic water bottle for more than three or four weeks. And if you’re concerned about baby bottles, glass or BPA-free plastic bottles are available.

Glenda, Hamilton

There are many stories spread via the internet about canola oil. It is claimed that it is a synthetic oil that’s not fit for human consumption. But we can all relax – this is not true.

A 2009 British Nutrition Foundation review of culinary oils and their health benefits found canola oil (also known as rapeseed oil) to be high in healthy monounsaturates and unusually high in ALA (the plant form of omega-3). A number of small-scale studies suggest the oil has a beneficial effect on heart health.

Our advice: Don’t worry. Canola oil is an economical, healthy oil.

Sandra, Masterton

While there may not be any research to support some of the claims found on websites (that eating like this will cure everything from cancer to constipation), in fact, there are definitely benefits from a more alkaline-forming diet and a number of eminent scientists are now researching this.

It’s thought an acid-forming diet contributes to bone loss and osteoporosis, as well as loss of lean muscle. Vegetables and fruits (including lemons and grapefruit) are alkaline forming. Grains and meat are acid-forming, dairy is slightly acid-forming and legumes neutral. Nine serves of fruits and veges each day are recommended for a more alkaline- forming diet.

Our advice: Eating more vegetables and fruit enhances health by increasing intakes of vitamins and minerals, fibre, antioxidants and other phytochemicals. It also increases the alkaline-forming balance in our diet, which can help protect our bones and muscles as we age.

David, Whangarei

There are many scary stories about soy foods. Among other things, it’s claimed soy will stunt growth and promote breast cancer. So it’s reassuring to know there is a vast amount of research around soy foods to say they are safe, and soy has been safely consumed as a major part of Asian diets for many years. Consumption of soy has been associated with reduced risk for a number of cancers and diseases of old age.

Our advice: Soy foods and drinks are safe to eat.

“Should I only eat fruit on an empty stomach?”
There’s nothing wrong with doing this, but you will get benefits from fruit whenever you eat it.

“Do I need to drink eight glasses of water a day?”
You just need to get about five to seven cups of fluid, which can come from drinks including water, tea, coffee, milk and juice. Needs increase with heat or exercise.

“Should I be eating for my blood type?”
No, there’s no scientific evidence to support the ‘blood type diet’.

“Should I switch back to butter, because it’s more ‘natural’?”
No, reduced-fat spread is still better for your health.

“Is food combining a healthier way to eat?”
No, there’s no scientific evidence to back this diet, and in practice, it’s really difficult to do.

“Are artificial sweeteners dangerous?”
Not according to current scientific evidence. They’re safe to consume as part of a healthy diet.

“Does drinking milk increase mucus?”
No, scientists have found no link between the two.

Goji berries

Goji berries are available as a dried fruit (which look like a red sultana) or juice. Marketers claim an endless list of health benefits such as promoting longevity, improving metabolism, treating impotence, preventing cancer and cleansing the blood. A study published in the Journal of Nutrition found that daily consumption of 120ml of goji juice was able to improve antioxidant markers in healthy adults.

Our advice: Goji berries appear to be rich in antioxidants, but claims about their benefits are not proven.


This naturally occurring no-kilojoule sweetener from plants (approved for use as a food additive in New Zealand in October 2008) is popular among those not keen on alternative sweeteners like aspartame. Stevia is 250-300 times sweeter than sugar and has a slower onset and longer duration of taste than sugar.

Our advice: Stevia is a no-kilojoule naturally occurring sweetener from plants that is totally safe to use.

Chia seeds

Chia seeds look a bit like tiny sesame seeds and come in black or white. Along with flaxseed, they are one of the richest sources of plant-based omega-3 known as ALA (alpha linolenic acid). They are also very high in soluble fibre. Chia seeds contain a variety of vitamins and minerals including iron, calcium, magnesium and potassium.

Our advice: Chia seeds are a rich source of plant-based omega-3 fats but are more expensive than other sources.


Acai berry is said to be a super antioxidant. While the juice or pulp of acai berries does exhibit antioxidant activity, a Brazilian study found it to be less potent than a number of other fruit including mango, strawberry, and grapes. And when Choice magazine (Australia) analysed nine different exotic juices made with goji, noni, acai or mangosteen, in all cases they found the total antioxidant activity of a 25-30ml serving of juice was less than that of a Red Delicious apple.

Our advice: Acai juice seems to be an expensive way to get antioxidants that could be obtained from other fruits or juices.