The food industry's biggest con trick is one you're probably falling for every day of the week. Even worse, the victims are your children.

Visit any supermarket and wander down the aisle of breakfast cereals. The message from the packets couldn't be more encouraging.

This one is 'the sunshine breakfast'. That one is made from 'wholesome corn, oats, rice and wheat'. Pretty much all are 'fortified with vitamins and minerals'. The contents of the attractive colourful boxes can form 'part of a balanced diet'.

© Unknown
Health hazard? According to Which? many breakfast products are laden with so much sugar they ought to be sold alongside chocolate biscuits.

For decades, we have been sold the story that a bowl of cereal is one of the healthiest things a caring mother could feed her children every morning.

But many cereals hide a horrible secret: the large amounts of sugar the manufacturers have pumped into them.

The research group Which? recently investigated the sugar content of 50 breakfast cereals. The results should shock you.

Products we are led to believe are healthy are, in fact, laden with so much sugar they ought to be sold alongside chocolate biscuits, said Which?, not marketed as a recipe for a healthy life.

The worst offenders in the Which? report were Kellogg's Frosties, with 37 per cent sugar; Tesco Choco Snaps, with 36 per cent; and Sugar Puffs, with 35 per cent. According to the Food Standards Agency, a sugar content above 15 per cent is considered to be high - these cereals have double this.

Perhaps it's not such a surprise that Frosties are sugary - after all, the sugar is visible on every flake. However, even Rice Krispies contain 10 per cent sugar, while Kellogg's Corn Flakes have 8 per cent.

Does it matter? The answer is 'Yes'. It is now accepted scientific fact that eating too much sugar increases your chances of suffering from obesity, diabetes, heart disease, cancer and liver problems.

A recent article in the highly respected journal Nature claimed that an excess of sugar contributes to 35 million deaths a year worldwide.

It not only makes people fat, but also changes the body's metabolism, raises blood pressure, throws hormones off balance and harms the liver, said the authors of the report, The Toxic Truth About Sugar.

'A little is not a problem, but a lot kills - slowly,' they said. They have called for sugar to be regulated like cigarettes.

The biggest risk of a high-sugar diet is obesity. This is not only because sugar is high in calories, but also because it acts like a drug on your system. Eating too much sugar leaves you craving more sugar. It becomes a vicious circle.

You've probably heard about the glycaemic index. This is a measure of how quickly foods release their sugars into your bloodstream.

Breakfast cereals have a high GI, which means they break down quickly during digestion and your blood sugar level surges. Then it quickly recedes - leaving you hungrier, sooner.

That's why people who have had cereal for breakfast can feel tired and hungry by 11am and unable to hold out for lunch.

Eating a bowl of Frosties is like throwing a newspaper into a fire. Whoosh, and then you need more fuel. The problem is that once the fuel has been used up, you need something sweet. Something right now. If you're not careful, you're soon into a spiral of obesity.

A breakfast consisting of an unsweetened yoghurt and a handful of fruit and nuts is like putting slow-burning coal on a fire: it will sustain you for longer and you won't crave the hit of a sugar fix.

Comment: Actually, a breakfast consisting of proteins and fats will sustain you much longer than any combination of sugar, fiber, dairy or carbohydrates.

So, if sugar is so bad for us, why do the cereal manufacturers pack their products with it?

To understand that, you need to know the economics of the industry. Breakfast cereals are a miracle of modern capitalism.

You take ultra-cheap ingredients - corn or rice, for example - put them through a simple manufacturing process and then sell them to the public at a huge mark-up. A 750g box of Kellogg's Frosties will cost you around £2.70. The corn will have cost Kellogg's just a few pennies.

However, there are two problems with this manufacturing process. It removes much of the nutritional benefits from the raw ingredients; and stripping grains of rice or pieces of corn, crushing them or puffing air into them leaves you with a product that is about as appealing in taste terms as eating newspaper.

This is where sugar comes in (and salt, but that's another story). Adding it in large amounts is the only way people can be encouraged to eat the end product.

Comment: Salt has also been demonized by the media. It is beneficial if unprocessed. The healthiest varieties are Celtic and Himalayan.

But this poses another problem for the manufacturers. How can you get away with marketing a product at children - the core customers for many breakfast cereals - if it's packed with all this sugar? The answer is as simple as it is dishonest: bestow the cereals with the illusory gift of health.

Enter the word 'fortified'. Emblazoned on pretty much every cereal packet, it's a subliminal and sneaky message to the consumer. This food may taste sweet, and sweet foods may seem unhealthy - but not this one!

By adding synthetic vitamins to your flakes, krispies or loops, the manufacturer can shout about the fact that a bowl of Kellogg's Coco Pops contains thiamin, riboflavin, niacin, vitamin B6, folic acid, vitamin B12, iron and calcium, without drawing attention to the fact 35 per cent of what you are eating is sugar.

That's around 3½ teaspoons of sugar in one 40g serving (assuming you measure out a serving, unlike most people, who pour until the bowl is full).

And if you add 125ml of semi-skimmed milk, which packs its own carbohydrate punch, that's a total of 5¼ teaspoons of sugar in your breakfast bowl. Marketing breakfast cereals as 'fortified with vitamins' is not against the law.

No outright lies are being told - those vitamins are there (though all the vitamins and minerals in fortified cereals are found in greater quantities in other foods, such as eggs and meat). But they're a smokescreen to distract attention from the real story.

Another ruse, which is used for cereals aimed at adults, is to label them as low-fat (the Special K packet declares: 'Less than 2 per cent fat').

Yes, cereal grains are by their very nature low in fat. But it's another red herring to distract you from the salt and sugar content. (And anyway, contrary to what we have been led to believe, there is scant evidence to support the nutritional mantra that fat is automatically bad for you.)

So there is nothing illegal in this marketing, but in my opinion it's dishonest. What's worse is when manufacturers plaster packets with cartoon characters and use cuddly creatures - the Honey Monster, Tony the Tiger, the Coco Pops monkey - to appeal directly to children.

The problem is that most of us don't understand the nutritional information on food packets. I have been a food investigative journalist for more than 20 years and it took me a while to get the hang of it.

When it comes to sugar, the key is to ignore the 'per serving' figure - the food company's bowl size probably will not equate to your children's portion - and look instead at the table marked 'typical values per 100g'.

Then look down to the figure next to 'sugars'. More than 15 per cent is deemed to be a high-sugar product - even Special K, which claims on its website 'you can be sure you are helping yourself look good and feel special' consists of 17 per cent sugar.

What should be done to end the scandal of sugary cereals? I think the Government should impose a sugar tax to discourage firms from lacing their products with the stuff.

But it would take a very brave government to pick a fight with the corporations that have built such lucrative businesses on the back of our addiction to sugar.

So, if you care about your children's health, you need to serve them something else for breakfast. I never gave my children sugary breakfast cereals: they had Weetabix served with a spoonful of fruit.

Other healthy starts to the day include a poached, boiled or sometimes fried egg, which provides every major vitamin you need apart from vitamin C; porridge, which is delicious and healthy; or a slice or two of wholemeal toast plus unsweetened yogurt mixed with fresh fruit and a handful of nuts.

Now grown up, my daughters won't touch foods that are packed with sugar - they find snacks and treats such as cupcakes to be too sickeningly sweet for their liking.

Thanks to a healthier breakfast, you can put your new-found energy to good use.

Read nutritional labels and learn how to understand them. And then get angry about the great cereal swindle.

Joanna Blythman is author of What To Eat: Food That's Good For Your Health, Pocket And Plate