BRITAIN??S fruit is becoming sweeter and its vegetables less healthy. A study has shown that modern farming methods and plant breeding are stripping produce of many of the nutrients essential for human health.

Over the past 60 years the levels of iron, magnesium and other minerals important for the body??s biochemical balance have declined by between a quarter and three-quarters in fruit and vegetables. The proportion of sugar has doubled in fruit such as apples and pears over the same period ?? partly to satisfy modern tastes.

The study comes amid increasing government concern at the degradation of the British diet and a surge in nutrition- related diseases such as obesity and diabetes, which some fear will overwhelm the National Health Service.

??What we found is that since 1940 the minerals and other nutrients that help to make fruit and vegetables good for you have been in startling decline,?? said David Thomas, the author of the paper.

He investigated how amounts of essential minerals such as iron, magnesium, potassium and copper had changed in 64 fruits and vegetables ?? and found that in almost every case they had fallen.

His research compared modern data with records taken from 1940, when government scientists began systematically analysing hundreds of foodstuffs, initially to work out the best diets for people with nutrition-related diseases such as diabetes.

It showed that, on average, vegetables had lost about half of their sodium and calcium content, a quarter of their iron and 76% of their copper content. The nutrient levels of fruits had also declined significantly with iron, copper and zinc all falling by up to 27%.

Thomas emphasised that fruit and vegetables were still far better than processed foods but warned that continued falls in nutrient levels ?? and rises in sugar ?? would be a problem.

Researchers have long suspected that dramatic changes in agriculture over the past 60 years could be changing the quality of the produce. However, the short-term benefits for farmers such as greater productivity, consistent quality and a wider range of varieties meant that these concerns attracted little attention.

Thomas, a mineralogist and fellow of the Geological Society, believed that the problem could be more serious because many essential nutrients such as selenium and molybdenum were not measured until quite recently.

His findings are supported by a study in the British Food Journal by Anne-Marie Mayer, a nutrition researcher at Cornell University, who found similar changes in the nutritional content of 20 fruits and 20 vegetables grown in Britain between the late 1930s and the 1990s.

??There were significant reductions in the levels of calcium, magnesium, copper and sodium in vegetables and in magnesium, iron, copper and potassium in fruits,?? Mayer said.

??The greatest change was the reduction in copper in vegetables to less than one-fifth of the old level.??

Both researchers link the decline to the intensification of farming. They suggest that agricultural chemicals and techniques could be depriving plants of the minerals.

Further evidence for the rising sweetness of fruit is provided by American government research, which found that apples can now comprise up to 15% sugar compared with 8%-10% three decades ago. Similar increases have been reported in a variety of other species including pineapples, pears and bananas.

Tom Sanders, professor of nutrition at King??s College London, said farming techniques had changed to meet consumer demand. ??For example, in apples this is partly due to new varieties and partly to how they are picked and stored ?? so that they retain more sugar,?? he said. ??As a rule, most fruit juice provides about 10 grams of sugar per 100 grams ?? about the same as Coca-Cola.??

Such trends have prompted the British Dental Association to reverse its health advice on apples. For years people were told that eating an apple was as good as brushing their teeth ?? until research found that fruit acids softened tooth enamel and the accompanying sugars promoted bacteria. Now dentists warn that consuming fruit and juice is a leading cause of tooth decay in adults.

The findings follow Food Standards Agency (FSA) research which shows that Britons are refusing to switch from diets high in fat, sugar and salt to more simple and natural foods.

The low levels of fruit and vegetables eaten by most British people make it all the more important that such foods should be as nutritious as possible, said Thomas.

The effects of poor diet were illustrated last week when the FSA published research into blood levels of vital nutrients.

Its National Diet and Nutrition Survey showed that the blood plasma of a quarter of British men and a third of women was iron-deficient and that many people may also be deficient in nutrients such as selenium and vitamins C and B12.

However, the FSA warns against drawing rapid conclusions on declining nutrient levels or on the need to take supplements. It suspects that figures collected 50 years ago cannot necessarily be compared with those of today because modern analytical techniques are different. It is about to conduct its own nutrient research.

An FSA spokesman said: ??Fruits and vegetables would not necessarily have been grown in similar conditions, soils or times of the year, or be the same varieties.

??A varied and balanced diet, with plenty of fruit and vegetables and starchy foods, will still provide all of the nutrients that a healthy individual requires.??

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