5 nutrition myths that need busting

23 September 2015

1. Don’t fry with olive oil

Extra virgin olive oil, a classic ingredient of Mediterranean diets, can be used for frying because it has a high smoking point (210°C), well above the ideal temperature for frying food at 180°C.

Olive oil will not change its structure at these temperatures so it will keep its nutritional value. Extra virgin olive oil is rich in antioxidants (phenolics and vitamin E) and the monounsaturated fat oleic acid, which helps keep it stable when heated.

Studies have shown that adding olive oil to vegetables helps make compounds such as phenolic antioxidants and carotenoids more available for absorption, and may just make people eat more vegetables because they taste better.

The best tip is to buy good-quality extra virgin olive oil in dark glass to ensure freshness and highest levels of antioxidants.

2. Vitamin C prevents colds

Regular vitamin C supplementation doesn’t prevent the common cold; that was the finding of a 2013 Cochrane review of the available evidence.

Vitamin C may reduce the severity and duration of colds but trials have found no consistent effect. Interestingly though, in those who are heavy exercisers, for example endurance athletes and soldiers, vitamin C supplements reduce the risk of developing colds by 52%.

It appears no research has been done to prove that a diet rich in fruits and vegetables reduces colds.

The top 5 fruits for vitamin C content per 100g are guava, kiwifruit, lychees, oranges and persimmons, and the top 5 vegetables,  capsicum, kale, broccoli, brussels sprouts and cauliflower.

Vitamin C dissolves in water, so avoid soaking fruits and vegetables. It's fine to steam and microwave them or, if cooking in water, use the water for stocks, stews and soups.

3. Potatoes are fattening

Not many studies have been found that assess the effect of eating potatoes on body weight. When potatoes are eaten as part of a healthy diet, they do not appear to cause weight gain. High-fat potato chips and crisps are another story.

Potatoes do contain carbohydrate, but in terms of energy potatoes have only 280kJ per 100g (equivalent to about 2 small new potatoes), which is the same energy content as a large banana or a dinner bread roll.

Potatoes generally have a moderate to high glycaemic index (53-93). The GI can be lowered if the skins are kept on, if they are cooked, cooled then eaten, if vinegar dressing is added or if lower GI varieties are consumed.

As a plant food, potatoes are rich in a variety of nutrients including vitamin C, B group vitamins, potassium, antioxidants (if they have coloured skins) and fibre (if skins are left on).

4. Sea salt beats table salt

Both sea salt and table salt are high in sodium, so one is not healthier than the other.

Depending on the source, salts may contain trace quantities of other minerals giving the salt a distinct colour and/or flavour. Table salt may have iodine added which may be important for pregnant women or those with iodine deficiency.

The upper level of intake for sodium for adults is 2300mg a day, with a recommended dietary intake of just 920mg a day. It’s estimated that Australians aged two years and older eat an average of 2150mg of sodium per day.

About 80% comes from processed foods and 20% from salt used at the table or in home cooking. Look for low-sodium food products (less than 120mg sodium per 100g) and only add salt to favourite foods, for example, eggs or tomatoes, rather than routinely adding to all foods.

5. Raw nuts beat roast nuts

There are few significant nutritional differences between dry/oil-roasted nuts and raw nuts (unless they are salted).

Most nutrients become slightly more concentrated during the roasting process as the nuts lose more moisture.

B group vitamins are not heat stable so their levels are reduced after roasting. The natural high fat content of nuts prevents any significant absorption of other fats into nuts even if they are submerged in oil. Only about 2—5% is absorbed, depending on the nut variety.

Eating a 30g serve of nuts (either raw or roasted) 5 to 7 times a week can reduce heart disease risk by 30—50%.  Roasted nuts can still lower blood cholesterol and even salted nuts may reduce blood pressure.

Lisa Yates

Lisa Yates is an Advanced Accredited Practising Dietitian with a Masters in Nutrition and Dietetics, graduating in 1995. Lisa runs her own private practice in Frenchs Forest Sydney and has interests in cardiovascular disease, diabetes, weight management, gastroenterology and sports nutrition.

Disclosure: Lisa Yates works for the Australian Tree Nut Industry.

Last Reviewed: 23 September 2015
Reproduced with kind permission from Medical Observer Weekly.

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References

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Lisa Yates

Lisa Yates

Lisa Yates is an Advanced Accredited Practising Dietitian with a Masters in Nutrition and Dietetics, graduating in 1995. Lisa runs her own private practice in Frenchs Forest Sydney and has interests in cardiovascular disease, diabetes, weight management, gastroenterology and sports nutrition.