“Go for gold” may not be a piece of health advice that you’re familiar with but it’s one that we’re supposed to be following. Rather than alluding to our sporting efforts, it refers to the colour that our food should be after we’ve toasted, baked, fried, grilled or roasted it.

Is burnt toast a health risk?

The worry is that scorched food – particularly bread and vegetables – contains acrylamide.

The nasty chemical is not something naturally present in what we eat. Instead, it forms in these starchy foods when cooked at temperatures higher than 120C. This is due to a reaction between the sugar it contains and a naturally occurring amino acid called asparagine. Boiling and steaming don’t produce acrylamide.

Acrylamide has been declared a “probable human carcinogen” by the International Agency for Research on Cancer (IARC). In essence, it means there’s strong evidence to show that the chemical can cause cancer in humans but there’s no conclusive proof.

Scientists believe the link may be down to glycidamide – a compound formed when the body breaks down acrylamide, says Oliver Jones, a professor of chemistry at RMIT University in Melbourne. Glycidamide can damage DNA, which is thought to contribute to cancer.

How much can I eat?

“I would stress that there is no evidence that the amounts of acrylamide that you are exposed to via burnt food are enough to cause cancer,” says Professor Jones.

The average slice of toast has about 4.8 micrograms of acrylamide, while a slice of burnt toast will have around double that (9.6 micrograms), he says.

Research suggests that it’s safe for people to eat up to 2.6 micrograms of acrylamide per kilogram of body weight per day. This means that the average man in the UK (85.4kg) could eat 23 slices of burnt toast every day, while the average woman (72.1kg) could eat 19.

“Eating that much bread would be far worse than the acrylamide,” says Professor Jones. “The question we should ask is not, ‘does something cause cancer?’ but ‘does it cause cancer at the level we are exposed to it at’? In the case of burnt food, the best evidence we have says that it does not.”

“There are other things like smoking and alcohol that are far more risky. So if you want to reduce cancer risk, burnt food is not where you should be starting,” he adds.

However, Andrew Sharrocks, a professor of molecular biology at University of Manchester is more cautious.

Studies show that damage caused by acrylamide is cumulative (meaning it can build up over time), he explains. This means that eating burnt food is “like Russian roulette”, and “the more you do this, then the worse the chances” of developing cancer, Professor Sharrocks says.

“Even small amounts of carcinogens are potentially dangerous if they cause damage in the wrong genes, maybe in cells that have already accumulated mutations over time,” he adds.

Are there other reasons to avoid burnt food?

As well as an unpleasant taste, burning toast – or cooking vegetables until they are blackened – can break down vitamins and other beneficial molecules, Professor Jones explains.

This means that burnt food “is not likely to be good for you”, says Professor Jones.

Research also shows that high exposure to acrylamide has been linked to poor brain health, reproductive problems among men and a lower birth weight among newborns.

How can you reduce your risk?

“We always recommend keeping the amount of acrylamide in our diets as low as possible,” says Mark Willis from the Food Standards Agency. Aim for a golden yellow colour or lighter when frying, baking, toasting or roasting starchy foods and following cooking instructions for packaged foods such as chips and roast potatoes, he says.

However, your overall diet is more important than acrylamide exposure when it comes to your cancer risk, says Maxine Lenza, a health information manager at Cancer Research UK.

“Some foods with acrylamide are high in calories, and being overweight or obese increases the risk of 13 types of cancer,” she explains. “So, aim to eat a healthy, balanced diet, with more fruit, vegetables and whole grains, and cut back on red and processed meats and foods high in fat, sugar and salt.”

The Telegraph, London