Have modern intensive farming methods – many of which solved malnutrition problems when they were first introduced – affected the mineral and vitamin content of what we eat?
In 2011, Donald Davis, a now-retired biochemist at the University of Texas, compared the nutrients in US crops from 1950 and 2009, and found notable declines in five nutrients in various fruits, including tomatoes, eggplants and squash. For example, there was a 43 per cent drop in iron and a 12 per cent decline in calcium. This was in line with his 1999 study – mainly of vegetables – which found a 15 per cent drop in vitamin C and a 38 per cent fall in vitamin B2.
Fruit and vegetables grown in the UK have shown similar depletions. A 1997 comparison of data from the 1930s and 1980s found that calcium in fresh vegetables appeared to drop by 19 per cent, and iron by 22 per cent. A reanalysis of the data in 2005 concluded that 1980s vegetables had less copper, magnesium and sodium, and fruit less copper, iron and potassium. The introduction of semi-dwarf, higher-yielding varieties of wheat in the green revolution of the 1960s means that modern crops contain lower levels of iron and zinc than old-fashioned varieties.
Davis and others blame agricultural practices that emphasise quantity over quality. High-yielding crops produce more food, more rapidly, but they can’t make or absorb nutrients at the same pace, so the nutrition is diluted. “It’s like taking a glass of orange juice and adding an equal amount of water to it. If you do that, the concentration of nutrients that was in the original juice is dropped by half,” says Davis.
Other scientists say that, although some nutrients are declining, the losses aren’t significant enough to warrant health concerns. Over the last century, lifespans have become longer, people are bigger and stronger, and a lot of that has to do with the food supply being better. There is a also problem with comparing cultivars being grown in the 1930s with often quite different strains of plant grown today, the year and the date of harvest. Methods of measuring nutrition have also changed.
The fact seems to be that differences in nutrient levels are relatively small. Most of us get enough iron, magnesium, and calcium. (adapted from an article in New Scientist by Chloe Lambert).
The problem may become worse with climate change. Last year, researchers at Harvard University warned that crops grown in the future will have significantly less zinc and iron, owing to rising levels of carbon dioxide. The team grew 41 different types of grains and legumes, including wheat, rice, maize, soybeans and field peas, under CO2 levels crops are likely to experience 40 to 60 years from now. They found that under these conditions, wheat had 9 per cent less zinc, 5 per cent less iron and 6 per cent less protein than a crop grown at today’s CO2 levels. Zinc and iron – but not protein – were also lower in legumes grown under elevated CO2. ( There will be three more postings on this important topic, if access to the internet, interrupted four times during the last few days, allows).