August 10, 2009
New Study Finds No Nutritional Advantage To Organically-Produced Foods
By Michael D. Shaw
In the most comprehensive study ever carried out on this topic, researchers from the London School of Hygiene and Tropical Medicine, under contract to Britain’s Food Standards Agency, found that there are no important differences in the nutrition content of organic food when compared with conventionally produced food. The study, entitled “Nutritional quality of organic foods: a systematic review” was published July 29, 2009 [Epub ahead of print] in the American Journal of Clinical Nutrition.
Based on an assiduously detailed protocol, Dr. Alan Dangour and team performed a literature search—using PubMed, Web of Science, and CAB Abstracts—covering the period 1 January 1958 to 29 February 2008. Hand searching of the reference lists of studies included in the review was conducted to check the completeness of initial electronic searches. In-press articles were identified by direct contact with key authors.
Peer-reviewed articles with English abstracts were included in the analysis if they reported nutrient content comparisons between organic and conventional foodstuffs. Two reviewers extracted study characteristics, quality, and data. The analyses were restricted to the most commonly reported nutrients.
From an initial pool of 52,471 articles, 162 relevant studies were identified (137 on crops and 25 on livestock products).
As a first criterion, articles were excluded which…
- Did not address composition of nutrients and other substances
- Did not present a direct comparison between organic and conventional production systems
- Were primarily concerned with the impact of different fertilizer regimes
- Were primarily concerned with non-nutrient contaminant content (cadmium, lead and mercury)
- Were authentication studies describing techniques to identify food production methods
From there, it was determined if the study were of satisfactory quality. Satisfactory quality publications provided the following:
- A clear definition, in the Introduction or Methods section of the paper, of the organic production methods of the crop or livestock product analyzed (including the name of any certifying body)
- Specification of the cultivar of crop, or breed of livestock
- A statement of which nutrient(s) and other substance(s) were assessed for content
- A description of the laboratory analytical methods used to test for the content of the named nutrients and other substances
- A statement of the statistical methods used for data analyses
The 162 studies were thus pared down to 55 of satisfactory quality, although data was tabulated from all studies. A total of 3558 comparisons of content of nutrients and other substances in organically and conventionally produced foodstuffs were extracted for analysis.
The nutrients and other substances measured for crops were nitrogen, Vitamin C, phenolic compounds, magnesium, calcium, phosphorus, potassium, zinc, total soluble solids, titratable acidity, copper, flavonoids, iron, sugars, nitrates, manganese, ash, dry matter, specific proteins, sodium, plant non-digestible carbohydrates, β-carotene, and sulfur. Based on the satisfactory quality studies, 20 of the 23 nutrients showed no difference. Nitrogen was higher in the conventionally produced, and phosphorus and titratable acidity were higher in the organic.
These differences were deemed not relevant to health, and are possibly related to fertilizer use, ripeness, and growing conditions.
As to the nutrients and other substances measured for livestock in the satisfactory quality studies, only the nitrogen content was different (higher in the organic). This difference was deemed not relevant to health, and is possibly due to differential use of nitrogen containing feeds and nitrogen content of the soil.
Most nutritionists are pleased with the findings, and are not terribly surprised. Reaction in the organic food products industry, as you might expect, has been less than positive.
The organic side has complained about the number of studies that were thrown out, implying that many of them contained data favorable to their side. The Organic Center (TOC) touts the finding that higher nitrogen in conventional crops is a “public health hazard” because of the potential for cancer-causing nitrosamine compounds to form in the human GI tract. Let’s be polite and call this assertion fanciful. At any rate, they don’t mention the higher nitrogen in organically-produced livestock products.
A further criticism offered by TOC is that the study did not include total antioxidant capacity among the nutrients studied. While this statement is literally true, it ignores the companion work, also performed by Dangour et al. entitled “Comparison of putative health effects of organically and conventionally produced foodstuffs: a systematic review.” This report has not yet appeared in a peer-reviewed journal, but does look at antioxidants, and offers this finding:
Eight studies specifically investigated foodstuffs known to be rich in antioxidants (for example tomatoes, apples and oranges), and six of these did not detect any statistically significant differences of organic and conventional foodstuffs on antioxidant activity.
Some on the organic side argue that they never have said that their products are more nutritious. Rather, they are safer because pesticides and synthetic fertilizers are not utilized.
There is an emotional appeal to this contention, but very little science to back it up. What studies that do exist mostly focus on endocrine disruptors, and few areas of biological chemistry have been more prone to poor quality work, as we have reported in previous articles. In any event, there are several natural compounds found in plants that themselves are powerful endocrine disruptors, and the effects of these disruptors are often health protective.
We are told by industry insiders that sales of organic food products have been affected by the economy, so this study is coming at a bad time. Still, it is anyone’s guess whether many minds will be changed in its wake.