Supporters of organic agricultural systems promote their exclusive use for a variety of reasons. These include: a dislike of large agribusiness; fear of health effects from traces of synthetic pesticides, bioengineered material, or irradiated products; concern about the environmental effects of conventional agricultural systems; and finally a belief that organic products are nutritionally superior to conventionally-produced ones.
Political positions aside, most of those concerns have little, if any, solid scientific support. But some of the myths surrounding organic foods are long-lived and appealing. Thus, it has become almost a mantra to assert that our conventional agricultural systems "deplete our soils," rendering the plants grown on them less nutritionally valuable for either animal or human consumption.
The basis for this statement is nebulous. To my knowledge, there has been little in the way of careful scientific analysis to support it. Even proponents of organic agriculture, such as retired Columbia University professor of nutrition education Joan Gussow, have acknowledged the lack of substantiating data.
Thus, a few weeks back, I was surprised to see a reference on a vegetarian website to a research article supposedly showing that organic produce was nutritionally superior to the conventional produce. In this article (by V. Worthington, in volume 7, issue 1 of the Journal of Alternative and Complementary Medicine), the author presents a survey of the scientific literature comparing the nutrient content of organic fruits, vegetables, and grains with that of their conventionally-raised counterparts.
The main problem in doing the survey, Dr. Worthington noted, was that the studies are quite dissimilar in terms of "crops grown, fertilization methods used, storage methods, if any, etc." She goes on to say that "These factors can make it hard to interpret data from such studies in any conclusive manner." But she does it anyway she says.
In all, Dr. Worthington found some 41 studies in the scientific literature published between 1946 and 1999. These reported the effects on nutrient content of differences in fertilization techniques either conventional fertilizers or strictly organic ones. But that's where any consistency seems to end.
The produce used to derive the data came from such varied locations as research plots and greenhouses, conventional storage facilities, and farm stands and markets. Further, for three of the studies, detailed descriptions of analytical methods were lacking this is problematic, as it is hard to believe that analytical techniques were constant over this long a time period. Data from all these types of studies were combined.
In the studies Dr. Worthington examined, she found 1,297 comparisons made between organic and non-organic produce. Oddly, she chose not to use 57 of those comparisons, saying they didn't report results in clear, numerical fashion. Perhaps excluding those comparisons was appropriate, but it should be noted that the majority of those studies were ones that concluded that organic and non-organic produce do not differ in nutrient content. That means that, deliberately or not, Dr. Worthington excluded results that did not support her conclusion that organic is superior. That wouldn't be troubling if she had consistently used very high standards in deciding which studies to include, but many of the ones she did include appear to have been inconsistent in various ways, as noted above.
In all, comparisons were made for 35 vitamins and minerals, as well as "protein quality and quantity." Protein quality was assessed by measuring the produce's content of essential amino acids, which were reportedly higher in organic crops. This is difficult to understand. A cabbage plant will make cabbage protein; it won't make corn, wheat, or beef protein, no matter how it is grown and the amino acid composition of its proteins are specified in its DNA. Thus, it's hard to see how the actual quality of the protein would be changed by fertilization methods.
Quantity is a different issue: surely a plant that doesn't receive appropriate nutrition might not grow normally or make the usual amount of protein. But here too, some more detail would be useful. For example, is there more protein in an organic cabbage than a conventional one? Is that because the organic one is larger? How were the data expressed? Usually, nutrients in foods are expressed per specific amount of a food. That is, the size of the food item or portion is specified. Thus, one might compare the protein or vitamin C in 3 ounces of organic versus conventional cabbage, but not just in "a cabbage." Further, a food scientist examines the content of nutrients on a dry weight basis, that is, after the water has been removed from the food. This practice allows one to control for the fact that produce can lose water during transport or storage sometimes a substantial amount.
Worthington uses the data from these varied studies to calculate percent differences in nutrients between organic and conventional crops. These differences are sometimes statistically significant, but it is not clear that they are really biologically significant. For example, she says that on average, the organic vegetables surveyed had 27% more vitamin C than the conventional ones. The author found this difference statistically significant. But whether or not it would make a difference to a person consuming the food would depend on the consitituents of the whole diet and which foods actually supplied that person's vitamin C.
Worthington did attempt to address this issue by estimating the nutrient content of the vegetable portion of a person's daily intake. In her discussion, she notes that while the conventional produce provides 67.9 mg of vitamin C, the organic one would provide 89.2. Thus, the organic one but not the conventional one would fulfill the adult male RDA for vitamin C. It's important to recognize, however, that even if these calculations reflect reality, they probably are not very important because this is not the vitamin C content of the whole diet: no fruits or grains were included, and much of the vitamin C in the typical American diet comes from fruit and fruit juices.
Yet another problem with the data used in this analysis is that no information is provided about the varieties of vegetables or fruits used in the studies. While a rose by any other name might smell as sweet, an Early Girl tomato will not necessarily have the same nutrient composition as a Beefsteak. According to Dr. Jack Francis, professor emeritus of food science at the University of Massachusetts in Amherst, there can certainly be large differences in composition due to genetic differences between strains. Such differences must be controlled for in any valid study.
In sum, Dr. Worthington made a valiant effort to show that organic methods produce nutritionally superior produce, but the data simply are not strong enough to allow her legitimately to do so. What we need are rigorously controlled studies of the same varieties of plants raised by either organic or conventional procedures. These plants must be grown at the same time, under the same conditions of weather. Further, if one wishes to determine whether differences in fertilizer types cause differences in nutrient content, then fertilizer type (organic vs synthetic) should be the only variable that differs between the plants the same pesticides should be used on both. And of course, one year's crop is not enough for a rigorous evaluation. Whatever the outcome, the data should be replicated to increase the validity of the data.
Without such careful study the issue can't really be settled, and we are left with only belief systems to fall back upon. Or, as the early computer programmers used to say, GIGO: garbage in/garbage out.