Do You Know the Nutritional Content of the Food You Eat?

Do you know the nutritional content of the food you eat?

For many years, the nutritional content of the food we eat has been carefully measured and published in a series of editions of the nutritionists, bible, McCance and Widdowson's Composition of Foods. It was recently noticed that the mineral content of a wide range of fruits and vegetables declined very substantially between the first edition, published in 1940, and the most recent edition, the sixth, published in 2002.

Some suggested that this was not a real decline but an artifact, caused by our modern and, it was claimed, more accurate measur­ing techniques. This theory was disproved when the older tech­niques were dusted off and found to produce the same lower values as the modern methods. Something else had to have caused the drop in mineral levels, and two plausible mechanisms have been identified.

First, there has been an evolutionary change in the fruits and vege­tables we eat, resulting from the use of intensive breeding pro­grammes to produce higher yields and enhanced disease resistance. It may be that the new varieties simply aren't as good at accumulat­ing minerals from the soil they are grown in. And second, agricul­tural techniques have changed. The routine use of deep ploughing and NPK (nitrogen, phosphorus and potassium) fertilizers has altered the micro-ecology of the soil in a way that many experts think has been damaging for the plants.

There is a particular group of micro-organisms in the soil called mycorrhiza (from myco = fungus and rhiza = root), which grow in very close association with the root systems of plants, in a rela­tionship which is probably symbiotic. It has been suggested that these micro-organisms assist the plant roots to take up mineral salts from the soil. Recent work by Dr Neil Ward at the University of Surrey and by others at Wareham has shown that deep plough­ing and the use of NPK fertilizers leads to a dramatic decline in the numbers of mycorrhiza, and a parallel decline in the mineral content of a number of food plants.

NPK fertilizers are used to promote crop yield, and have undoubtedly helped to improve agricultural productivity. But it now seems that while crop yield improves, its mineral content may be going in the opposite direction. And there have been other changes in the plant foods we eat, changes which have been caused by pressure from retailers and, to some extent, from consumers.