Shoppers pay more than a third more for organic food in the belief that it has more nutritional content than food grown with pesticides and chemicals.
However, the new research by Dr Susanne Bugel and colleagues, from the Department of Human Nutrition, shows that there is no clear evidence to support this belief.
In the first study ever to examine the retention of minerals and trace elements, animals were fed a diet consisting of crops grown using three different cultivation methods in two seasons.
Researchers looked at the following crops - carrots, kale, mature peas, apples and potatoes - staple ingredients that can be found in most families' shopping list.
The first cultivation method involved growing the vegetables on soil, which had a low input of nutrients using animal manure and no pesticides except for one organically approved product on kale only.
In the second method, researchers applied a low input of nutrients using animal manure, combined with use of pesticides, as much as allowed by regulation.
The third method comprised a combination of a high input of nutrients through mineral fertilisers and pesticides as legally allowed.
The crops were grown on the same or similar soil on adjacent fields at the same time and so experienced the same weather conditions.
All were harvested and treated at the same time. In the case of the organically grown vegetables, all were grown on established organic soil.
After harvest, researchers found that there were no differences in the levels of major and trace contents in the fruit and vegetables grown using the three different methods.
Produce from the organically and conventionally grown crops was then fed to animals over a two-year period and intake and excretion of various minerals and trace elements were measured.
The results showed there was no difference in retention of the elements regardless of how the crops were grown.
"No systematic differences between cultivation systems representing organic and conventional production methods were found across the five crops so the study does not support the belief that organically grown foodstuffs generally contain more major and trace elements than conventionally grown foodstuffs," Dr Bugel said.
The research is published in the latest issue of the Society of Chemical Industry's (SCI) Journal of the Science of Food and Agriculture.