Monday November 8 2010
Organic or not, vegetables are a great source of vitamins
“Organic vegetables are no healthier than food grown conventionally,” The Daily Telegraph has reported. The newspaper said that a scientific study had grown vegetables under both organic and conventional conditions but found no difference to the levels of polyphenol compounds they contained.
It has been suggested that polyphenol antioxidants may reduce the risk of dementia, cardiovascular disease and some cancers. However, their effects have only been observed in laboratory studies of cells, and their health benefits in humans have yet to be confirmed. In this research, the levels of polyphenols in the crops were the same, regardless of the use of organic methods or pesticides and inorganic fertilisers.
This study suggests that organic farming methods do not increase the quantity of polyphenol antioxidants in a number of crops. However, for many people the decision to eat organic may be a lifestyle one, influenced by factors such as taste and preferring farming methods that do not use pesticides.
Fruit and vegetables have numerous benefits far beyond their antioxidant content and, organic or not, it is important to try to eat at least five portions each day.
Where did the story come from?
The study was carried out by researchers from the National Food Institute in Denmark, the University of Copenhagen and Aarhus University. It was funded by the Danish Ministry of Food, Agriculture and Fisheries. The study was published in the peer-reviewed scientific publication, The Journal of Agricultural and Food Chemistry.
The research was well described by a number of newspapers, which mostly to balance some of the theoretical benefits of polyphenols with the fact that the benefits of consuming antioxidants are not well established. For example, the Daily Express pointed out that some of the possible benefits were based on the results of laboratory experiments on cells, and that it is not clear whether these benefits apply to people. The Daily Telegraph reported that perceived health benefits are not the only reason that some people chose to buy organic produce, although it failed to point out that these health benefits are unproven.
What kind of research was this?
The researchers set out to examine whether the nutritional content of carrots, onions and potatoes was affected by the methods used to grow them. They specifically looked at polyphenol antioxidant compounds such as flavonoids and phenolic acids. They also wanted to assess whether the concentrations of these compounds varied in different locations, soil types, and the years in which the vegetables were grown.
This study aimed to look at the basic science of how farming methods affect the crops, and did not involve any aspect of research into how animals or people absorb nutrients from food, or what impact this might have on health.
This was an appropriate study design for investigating whether different farming methods had a different effect on the nutritional composition of a number of crops. It cannot be used, however, to define the wider health benefits of consuming fruit and vegetables grown by different methods, as polyphenol antioxidants are only one aspect of nutrition, and the health benefits of consuming them are not fully understood.
What did the research involve?
Potatoes were grown in a crop rotation experiment in three different locations from 2007 to 2008. Carrots and onions were grown at one location as part of another crop rotation experiment. In both sets of experiments, the crops were grown under three systems: one ‘conventional’ (using pesticides and inorganic fertiliser) and two organic systems (both using animal manure, but one also adding ‘cover crops’, which are used to improve soil fertility).
To compare the nutritional content of the vegetables, the crops were harvested on the same day in all farming systems, and a 15kg sample of each vegetable crop was collected for analysis. From these, slices were taken, then processed and preserved by freeze-drying. The samples were subsequently analysed in a laboratory, where the levels of flavonoids in onions and phenolic acids in potatoes and carrots were measured.
What were the basic results?
Levels of flavonoids in onions were not found to vary between the different farming systems, although within each farming system there were variations in the levels of all the flavonoids measured. This variation occurred despite the researchers taking samples grown near each other to reduce any possible effect of microclimate or differences in soil fertility.
The farming system used made no difference to the overall levels of phenolic acid found in carrots. However, within each system, carrots showed a greater variation in phenolic acid levels than the potatoes did. In the potatoes, levels of one phenolic acid (5-CQA) were found to be higher in the organic system using cover crops than in the conventional system.
Within each system, there was some year-to-year variation in the levels of one of the flavonoids in onions. This may have been due to different weather conditions in each of the study years.
How did the researchers interpret the results?
The researchers reported that they found “no significant differences in the content of flavonoids and phenolic acids between the conventional and the two organic growth systems”. They speculated that the higher levels of one phenolic acid in potatoes in the second organic system may be due to them being grown on a different farm.
They conclude that levels of synthesis of the compounds analysed did not differ according to the growth conditions, location or the year the crops were grown in.
This study suggests that organic farming methods do not affect the concentration of polyphenol antioxidants in a range of vegetables when compared with other farming methods. However, it should be noted that the research did not assess other aspects of the nutritional composition of crops, nor did it look at whether eating organic produce had any other health benefits.
The exact benefits of polyphenol antioxidants are not fully understood, and they only account for one of the numerous nutritional benefits from eating fruit and vegetables. As such, this study alone does not definitively answer the question of whether or not organically grown produce has different health benefits to crops grown by other farming methods.