From fresh fruit to ready meals, from baby formula to sausages, the food we eat is getting sweeter. Why? And should we be worried? Felicity Lawrence examines the sugaring of the British palate

Once, sugar was all delight: from the land of milk and honey to Shakespearean innocence - "white-handed mistress, one sweet word with thee ... honey, milk and sugar, there is three". But now it's the devil incarnate; or, at least, the new nicotine.

"Sugar is as dangerous as tobacco [and] should be classified as a hard drug, for it is harmful and addictive," according to a recent article in the British Medical Journal. Sugars in all forms are seen by many as dangerous to health and our food is packed full of them: not just sucrose (plain sugar as we know it) but other forms of refined sugars from cane, beet and corn.

Eat too much of them and you may become fat, sick and miserable. Sugars rot your teeth and encourage a calorie-rich but nutrient-low diet that contributes to obesity - and obesity is a high-risk factor for heart disease, diabetes and certain cancers.

The rhetoric from the government's food standards agency is more muted but the aim is the same: having waged a successful war against excess salt, next on the watchdog's agenda is shifting the balance of our diets away from processed sugars and fats to less energy-dense and more nutritious foods. It has begun the drawn-out process of consulting industry and health groups on what should be done and is expected to ratchet up the campaign over the next few months.

The watchdog is focusing on both sugar and fat because they are closely linked in food manufacturing: reduce one and the other has a tendency to go up. The health-conscious have been reducing their fat consumption for a while, but if they've been doing it by eating more reduced-fat products, such as low-fat yoghurts, or "lite" mayonnaise, or reduced-fat biscuits, then they will be eating more sugars instead.

But how have we become so devoted to sugar? And what has the sweetening of our diets done to our palates along the way?

At East Malling research station in Kent, Vicky Knight is a raspberry plant breeder, Dave Simpson a strawberry expert and Ken Tobutt an apple, cherry and rootstock man. I took them a bag of supermarket fruit and they used a Brix refractometer, an instrument used by industry to measure sweetness, to test the sugar content of my purchases.

Foods are definitely getting sweeter and our palates altering, say the East Malling plant breeders, but when it comes to fresh produce the change is more subtle than just upping the sugar content. "Our perception of fruit varieties and their taste is affected by acid levels. People tend to talk about things being sweeter but sometimes what's actually happened is they've become blander. You can eat blander fruit in larger quantities, you come back for more of it than of the richer varieties, and that can increase sales," Tobutt explains.

Apples and strawberries, for example, have been bred to taste sweeter by greatly reducing their acid levels. The problem is that if acidity is too low, the fruit is left with little flavour at all - just sweetness.

Many breeds of raspberries are also a lot sweeter. It used to be that it didn't matter that the fruit was sharp because sugar was added by consumers (and a third of the crop went for jam). But now most raspberries are sold fresh through supermarkets. "A new variety, the Canadian Tulameen, was released in 1989," says Knight. "It has a higher Brix score for sweetness than some older varieties, so all new varieties being tested for market are now compared with a sweeter standard than 10 years ago, and supermarkets will reject them if they are not sweet enough," Knight says. She crushes a handful of the raspberries I have brought in a pestle and mortar. "There's no smell at all, but a slightly bitter undertow to the taste as though you could be chewing the leaves of the plant." But they are sweet on the Brix measure, showing as 10% sugars - about the same sweetness as a milkshake.

Next Knight casts her experienced eye over some apples in a plastic, cling-wrapped tray: British Cox, grown in Kent, sell-by date January 31. "They'll be more than four months old now, picked mid-September, I guess, and kept in modified atmosphere storage to switch off the ripening mechanism." She sniffs. "Zero aroma." The new variety, Pink Lady, sell-by date January 30, has what breeders call good crunch, but it tastes unpleasantly sweet to me. According to the Brix measure it is 12.5% soluble sugars, high but not that high, but it probably tastes so sweet because there were few other flavours to counteract it. The Cox tastes much less sweet but has more depth and complexity of flavour. Its sugar levels are surprisingly higher on the Brix measure, at 16%, but are balanced by greater acidity.

Red grapes turn out to be the sweetest of the fruits I take. A new trademarked variety called Absolutely Pink from South Africa, these were indeed very more-ish, little explosions in the mouth of sweet liquid with no clearly identifiable flavour, more like a sweetened drink than a fruit. "Ooh, they are absolutely tasteless," Knight says, handing me the refractor for inspection. "But look, they are staggeringly high on the Brix. Twenty per cent soluble sugars. Exactly what we said, all sugar and no real flavour." That 20% compares with an average of 16% sugars recorded in red grapes in 1940 in the official bible of food analysis, The Composition of Foods.

We are born with an attraction to sweetness, taking our first gulps of it in the womb, when we swallow amniotic fluid. The evolutionary explanation is that this is how we learned to distinguish foods that are generally safe - since there is nothing in nature that is sweet and poisonous - from bitter edibles that may contain toxins.

Breast milk, too, is sweet. But flavours from the mother's diet during pregnancy and after birth are transmitted both to the amniotic fluid and to breast milk, so that breast-fed babies experience not only sweetness but a wide range of tastes from sour to spicy. This early exposure to a varied diet makes them more likely than bottle-fed babies to try a range of new flavours later.

Sugar, say its fans, helps make new foods palatable. East Malling Research's chief executive, Colin Gutteridge, worked for Cadbury Schweppes for 23 years before joining the research station and can see a "taste evolution". "I remember being presented with yoghurt for the first time when I was nine. It was acidic and I thought it was repulsive. If there is a trend over the past 100 years it is taking products that are marginal in taste and making them more acceptable to a wider range of people by adding in sweetness. Does any of this matter? Personally, I don't think so. Without it I would never have enjoyed yoghurt."

A whole science has grown up to try to understand how our early taste preferences are formed and how these may affect the way we eat later, with much of the cutting-edge research being conducted at The Monell Chemical Senses Center in Philadelphia, a research establishment that is part-sponsored by the food and drink industry. "Babies around the world can detect sweet tastes at birth and can distinguish between different types of sugar," says researcher Dr Julie Mennella. Mennella has also shown that sweet tastes can act as analgesics and reduce the sensation of pain in children. "The heightened taste for sweetness occurs during periods of maximum growth and doesn't diminish until after adolescence, suggesting we crave sweetness when we have the greatest need for density of calories."

Bitter tastes, on the other hand, are learned. Before mass industrialisation of the diet, culinary traditions helped in the process of getting young children used to foods that are not sweet but are valuable sources of vitamins and minerals.The problem now is that there is a mismatch between our food supply and our biology. Weaning on manufactured baby foods means that we take our palates in a different direction. Before the 1970s few parents used processed baby foods, but now they are regularly served up by a large numbers of parents as their confidence in what is wholesome and safe has disappeared. Although few baby-food manufacturers supplying Europe add sucrose to their products these days, they are often very sweet, making use of concentrated fruits such as apple and sweet vegetables such as sweet potato. A 213ml jar of junior baby food apple and blueberry has 33g of sugars, for example - that's the equivalnent of 11 sugar cubes. Baby vegetable purees are noticeably sweet - 12g of sugars in a 213ml jar of sweet potato, for example; meat dishes have an underlying sweetness too: beef and spaghetti has 4g of sugar per jar.

The way baby foods are processed plays a part too, according to Gerrie Hawes, who used to work for a leading baby-food maufacturer and now runs her own baby-food company, Fresh Daisy. "Nearly all are long-life products. The process involves cooking the food once, putting it in jars and then cooking it again in the jar under pressure to 121C or more for up to 40 minutes. The high temperature achieves the desired sterilisation of the food but also changes the taste, texture and colour; it caramelises the sugars in fruit and vegetables. Babies acquire a taste for that caramelised flavour. Home-cooked food is different, it has a graininess and mix of flavours even when pureed that manufactured food does not."

The food industry, of course, is reluctant to surrender the power this sweetness has over its young customers. Global standards for foods are set by the international Codex Alimentarius Commission and these are increasingly used as benchmarks in World Trade organisation meetings. At the last meeting of Codex in November 2006, the Thai government introduced a proposal to reduce the levels of sugars in baby foods from the existing maximum of 30% to 10%, as part of the global fight against obesity. The proposal was blocked by the US and the EU.

Patti Rundall, policy director of Baby Milk Action group, is convinced such early exposure to refined sugars is how babies get hooked on sweetness at the point at which they would otherwise be weaned off it. "You are altering the taste profile and palate of babies. Follow-on formulas are often incredibly sweet, and can contain 60% more sugars than regular milk." She points out that several research studies have shown correlations between bottle feeding and subsequent obesity. "A bottle-fed baby consumes 30,000 more calories over its first eight months than a breast-fed one. That's the calorie equivalent of 120 average chocolate bars. It's hugely important to obesity."

For a palate trained this way it is only a short step to sweetened snack foods and to foods claiming to be healthy that are anything but. Fruit-flavoured yoghurts have not simply had their sourness reduced, they can be sweeter than a chocolate mousse and be up to a fifth sugar. A "light" strawberry yoghurt may be virtually fat-free but it is 7% sugars, with not only added fructose but extra artificial sweetening too.

Even salty snacks are sweetened - Pringles Originals are flavoured with dextrose; some children's crisps are sweetened with aspartame; while upmarket crisps may be sugared with "sea salt and black pepper flavouring" that contains the milk sugar lactose, or with "sea salt and west country cider flavouring" that contains not a hint of west country cider but milk sugar, sugar and flavouring instead. A whole new marketing language has been created to signal sweetness in supposedly savoury foods: spicy Moroccan, Thai sweet chilli, caramelised onion, balsamic vinegar.

The staples are not immune either. Look at the nutritional label on a traditionally-made cheese and the line for sugars will read zero. Pick up a cheese spread or processed children's cheese and you can find it contains 6% sugars, thanks to the milk sugars in the skimmed milks powders from which it is manufactured. Pizzas, buns for burgers, sausages and ready meals all get sweetened. Beer is the same: learning to like the bitter taste of ale is no longer an adult rite of passage. "Industrial global beer brands are being dumbed down. They are not necessarily sweeter but they are less bitter and blander. Manufacturers use fewer hops and rather than using malt, bulk them out with brewing sugars," says the Campaign for Real Ale's research manager, Iain Loe.

Campaigners think it does matter. "We are raising our current generation in the sweet shop," says Neville Rigby, director of policy at the International Obesity Taskforce. "Sweets themselves are ubiquitous but the food industry also has some 30,000 varieties of chemical powder to tweak their artificial ingredients in other products to make them sweet. Why do they add sugars to savoury products? Presumably because their research tells them children like it, and it sells."

The reason all these sugars are both attractive and pernicious is that our physiology is geared to eating food in its whole, natural state rather than concentrated form. Refined sugars, and highly refined carbohydrates generally, are converted very rapidly to blood sugar which gives you a burst of energy and a high - rapidly followed by a low as the pancreas releases insulin to reduce blood-sugar levels, leaving you hungry for yet more sugars. Moreover, if up to a quarter of your calories are coming from the empty calories of refined sugars, the sugars inevitably displace fresh food with vitamins and minerals. You simply don't get enough nutrition.

"The blood sugar curves are quite different with whole foods. They give you a feeling of satiety and fullness and are metabolised slowly so that energy is released steadily over a longer period," says Aubrey Sheiham, emeritus professor of public health at University College, London. "But as you expose yourself to sugar, your liking for it increases, and your taste threshold changes. You start needing more. Manufacturers have exploited that." Intriguing evidence is also beginning to emerge that explains why high sugar consumption becomes quite so addictive. In animal experiments at Princeton University, Carlo Colantuoni has shown that rats that have been fed large amounts of sugar in their food and then have it removed show signs of opioid withdrawal. "The indices of anxiety and other symptoms were similar to withdrawal from morphine or nicotine," he reports in the journal Obesity.

The industry will have none of this. It still maintains through its trade organisations such as the Food and Drink Federation that all calories are equal; the developed world's obesity epidemic is, it says, the result of too many calories consumed compared with the number of calories expended through physical activity. British Sugar, which controls 60% of the UK domestic market, follows the typical line on its website: "Sugar is a natural carbohydrate ... a source of glucose, the vital fuel for the brain and body ... an essential part of an active lifestyle."

If our palates have indeed been sweetened, you would expect to see it in consumption figures. But the Department for Environment, Food and Rural Affairs cheerfully announced last month that the latest statistics from the official Expenditure on Food and Drink survey show that fruit and vegetable intake was 7% up year on year for 2005-6, while confectionery purchased for the household was down 6%, and our total intake of added sugars also fell, albeit only a fraction of a per cent.

Sadly, it looks as though we may all be telling something less than the truth. The EFS data is collected from self-reported diaries. Research at the Medical Research Council's human nutrition unit in Cambridge has shown that people under-report their consumption by up to 34%. Market analysts Taylor Nelson Sofres, by contrast, collects its statistics from till receipts of what has actually been sold. Their figures for the year to December 2006 shows that sales of small bottles and cans of drink were up 34%, cakes were up 2%, chilled juices and juice drinks were up 30%, and chocolate biscuit bars were down 9%, but that fall was made up more than three times over by a rise in chocolate confectionery sales, which were up 5%, from £1.6bn in 2005 to £1.7bn in 2006.

Sales of sweetened soft drinks overall have fallen slightly in the past couple of years, as fresh fruit juice sales have risen, but they remain far higher than a decade ago. In 1992 we drank 1.5l of soft drinks per person per week; that rose to about 1.8l in 2003/4, and dipped down to about 1.7l in 2004/5. (Most of this, 1.4l, is sugared, not low-calorie.) And even the fruit juice seems to be getting sweeter. Sainsbury's has started selling a fresh pressed, not from concentrate, red merlot grape juice that is delicious but contains a breathtaking 44g of sugars per modest serving. That is more than in a can of cola, albeit in a different form. A traditional pressed apple juice next to it on the shelf has 27g of sugars per serving.

Accurate figures on how consumption patterns have changed over a longer period are hard to come by, because the way data is collected has been changed. But Barry Popkin at the University of Carolina has looked at more than 100 countries going back to 1962. In his report The Sweetening of the World's Diet, he shows that as the gross national income per capita of a country goes up with industrialisation, so too does consumption of sugars. As populations have become urbanised and dependent on processed foods, the number of calories they get from sugars has increased by a third.

It has been on the increase for some time. At the beginning of the 18th century, per capita consumption of sugar in England was still only about 4lbs - less than two of today's packets of sugar; by the beginning of the 19th century consumption had soared to 18lbs per person per year. Sugar, produced by slaves and imported from the colonies, fuelled the industrial revolution. In the form of sweetened tea and jam, it fed the factory workers of the 19th century. By the 1890s, the price greatly reduced after the abolition of slavery by the removal of free-trade barriers, it had become a necessity in the labouring diet: consumption touched 90lbs per person per year.

Today, boys and girls in this country get 16-17% of their daily calories from processed sugars when the maximum recommended by experts, if you want to avoid diet-related diseases, is 10%. (There is no physiological need to eat any refined sugars at all.) By the age of seven children are eating an average of half a kilo of sugary foods a day. By the age of 15 boys typically have a habit of nearly 80lbs per year, the equivalent of 1,000 cans of cola or 11,800 sugar cubes, and that's only counting what gets owned up to in food diaries. Taking into account under-reporting, they are matching or exceeding the consumption of impoverished manual workers of the 19th century whose requirement for calories was determined by 14 hours or more of physical labour a day.

For the food industry, cutting back on sugar is far tougher than dealing with salt. Sugars have so many functions, quite apart from sweetening. They add cheap bulk. They draw off moisture, prolonging shelf life. They are so valuable to the economics of the business, in fact, that far from reducing sugars, a new class of additives has been developed to disguise them. "Sweetness modifiers", which may be labelled as "flavouring", prevent the taste receptors in the mouth registering sweetness. They are recommended in trade catalogues for processed foods such as cheese, meat and salad dressings where sugars are being added at levels that "taste wrong", even to our bamboozled senses.

The guilt associated with the pleasure of sugar used to arise from slavery - "When we work in the sugar mills and catch our finger in the millstone, they cut off our hand; when we try to run away, they cut off our leg ... it is at this price that you eat sugar in Europe," says the native of Surinam in Voltaire's Candide. Today there is a different kind of guilt, at the possibility that we might be harming ourselves - without knowing how.