The primary reason for the decline in nutrient content and quality of several foods is the way the food is grown, processed and prepared, according to Donald Davis, a biochemist at the University of Texas.
"High-yield crops grow bigger or faster, but are not necessarily able to make or uptake sufficient nutrients to maintain their nutritional value," said Davis at a recent meeting of the American Association for the Advancement of Science (AAAS) in St Louis.
Recent studies of vegetables, fruits and wheat have revealed a 5 to 35 percent decline in concentrations of some vitamins, minerals and protein over the last half-century, a phenomenon that has come to be known as 'the dilution effect.'
And according to Davis, an important research goal would now be to find ways to maintain yield levels while reversing dilution effects.
Other changes in agriculture during the last 50 years include the widespread use of pesticides, plant growth regulators, and highly soluble sources of plant nutrients, along with decreased use of humus-containing fertilizers.
Recent studies, which have tested the effects on antioxidant levels of reversing these changes, have revealed that several organic growing methods can increase the broad antioxidant content of produce.
"On average, antioxidant levels increased by about 30 percent in carefully designed comparative trials," said Davis. "Organically grown produce offers significantly enhanced health-promoting qualities, contributing to the achievement of important national public health goals."
But fruits and vegetables are not the only products becoming less nutritious. Dr David Thomas, a primary healthcare practitioner and independent researcher recently made a comparison of government nutritional tables published in the UK in 1940, and again in 2002. His findings, which were published by the Food Commission last month, certainly make for alarming reading.
For example, the iron content in 15 different varieties of meat had decreased on average by 47 percent, with some products showing a fall as high as 80 per cent, while the iron content of milk had dropped by over 60 per cent.
Copper and magnesium, essential for enzyme functioning, also showed losses in meat products. Magnesium levels have typically fallen by 10 per cent while copper levels have fallen by 60 per cent.
Thomas argues that the gradual degradation of the micronutrient value of food must be tackled by industry, consumers and regulators.
And perhaps the most immediate way to overcome this deficiency is through the use of functional food ingredients.
Indeed, the market for functional food has soared in recent years, on the back of a growth in demand for vitamin-fortified, heart-healthy and organic food. Increasingly, companies are developing healthier products and using health messages in their marketing campaigns.
The recent AAAS symposium highlighted how consumers need to select foods naturally high in antioxidants and vitamins, and learn how to prepare and store them in ways that retain antioxidants.