Fergus Walsh Medical correspondent
Media captionExperts say bread should be cooked to a golden yellow colour to reduce our intake of a harmful chemical
Bread, chips and potatoes should be cooked to a golden yellow colour, rather than brown, to reduce our intake of a chemical which could cause cancer, government food scientists are warning.
Acrylamide is produced when starchy foods are roasted, fried or grilled for too long at high temperatures.
The Food Standards Agency (FSA) recommends carefully following cooking instructions and avoiding browning.
However, Cancer Research UK said the link was not proven in humans.
The FSA also says potatoes and parsnips should not be kept in the fridge.
This is because sugar levels rise in the vegetables at low temperatures, potentially increasing the amount of acrylamide produced during cooking.
Acrylamide is present in many different types of food and is a natural by-product of the cooking process.
The highest levels of the substance are found in foods with high starch content which have been cooked above 120C, such as crisps, bread, breakfast cereals, biscuits, crackers, cakes and coffee, as a result of the roasted beans.
It can also be produced during home cooking, when high-starch foods - such as potatoes, chips, bread and parsnips - are baked, roasted, grilled or fried at high temperatures.
When bread is grilled to make toast, for example, this causes more acrylamide to be produced. The darker the colour of the toast, the more acrylamide is present.
During the browning process, the sugar, amino acids and water present in the bread combine to create colour and acrylamide - as well as flavour and aromas.
The Food Standards Agency says it is not clear exactly how much acrylamide can be tolerated by people, but it does believe that we are eating too much of it.
So, as a part of a new campaign, it is advising people to make small changes to the way they cook and prepare food, including:
- Go for a golden yellow colour when toasting, frying, baking, or roasting starchy foods such as potatoes, bread and root vegetables
- Don't keep raw potatoes in the fridge - store them in a cool, dark place above 6C instead
- Follow the cooking instructions carefully when heating oven chips, pizzas, roast potatoes and parsnips
- Eat a healthy, balanced diet that includes five portions of vegetables and fruit per day as well as starchy carbohydrates
What's the risk?
Research in animals has shown that the chemical is toxic to DNA and causes cancer - so scientists assume the same is true in people, although as yet there is no conclusive evidence.
The possible effects of acrylamide exposure include an increased lifetime risk of cancer and effects on the nervous and reproductive systems.
But whether or not acrylamide causes these effects in humans depends upon the level of exposure - and some are not convinced that there is any real danger to public health.
David Spiegelhalter, professor for the public understanding of risk at Cambridge University, said he was not sure the advice was appropriate.
He said: "Even adults with the highest consumption of acrylamide would need to consume 160 times as much to reach a level that might cause increased tumours in mice.
"The FSA provide no estimate of the current harm caused by acrylamide, nor the benefit from any reduction due to people following their advice."
Image copyright Thinkstock Image caption Cancer Research UK says crisps, chips and biscuits are major sources of acrylamide
Smoking exposes people to three to four times more acrylamide than non-smokers because the chemical is present in tobacco smoke.
As well as advising the public, the Food Standards Agency is also working with industry to reduce acrylamide in processed food.
And there has been some progress - between 2007 and 2015, it found evidence of an average 30% reduction in acrylamide across all products in the UK.
Steve Wearne, director of policy at the Food Standards Agency, said most people were not aware that acrylamide even existed.
"We want our campaign to highlight the issue so that consumers know how to make the small changes that may reduce their acrylamide consumption whilst still eating plenty of starchy carbohydrates and vegetables as recommended in government healthy eating advice.
"Although there is more to know about the true extent of the acrylamide risk, there is an important job for government, industry and others to do to help reduce acrylamide intake."
Emma Shields, health information officer from Cancer Research UK, acknowledges that acrylamide in food could be linked to cancer - but she says the link is not clear and consistent in humans.
"To be on the safe side, people can reduce their exposure by following a normal healthy, balanced diet - which includes eating fewer high calorie foods like crisps, chips and biscuits, which are the major sources of acrylamide."
She said there was many other well-established risk factors for cancer "like smoking, obesity and alcohol which all have a big impact on the number of cancer cases in the UK".
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