Some say the way we produce and process food making it less nourishing than in our grandparents’ day. New Scientist looks at the facts

VEGAN, low carb, Palaeo, 5:2. The quest for the healthiest diet shows no sign of abating. We now know more than ever about what food does to the body and the importance of antioxidants, healthy fats and a low glycaemic index.

But what if, all the while, our food has been getting less nutritious? What if modern intensive farming methods – many of which solved malnutrition problems when they were first introduced – have affected the mineral and vitamin content of what we eat? Could having a constant supply of varied produce be compromising its goodness?

Some of the most eye-catching work in this area has come from Donald Davis, a now-retired biochemist at the University of Texas. In 2011, he 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 (see table).

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.

Davis and others blame agricultural practices that …