NEW EVIDENCE SETTLES A LINGERING QUESTION -
IS ORGANIC FOOD MORE NUTRITIOUS?
Forty New Studies Published in Last Six Years Provide a Firm Foundation
for Some Clear-cut Answers: Yes, Organic Plant-Based Foods ARE More Nutritious,
and Provide on Average a 25% Nutrition Premium
BOULDER, Colo. - March 18, 2008 - A comprehensive review of
97 published studies comparing the nutritional quality of organic and conventional
foods shows that organic plant-based foods (fruits, vegetables, grains) contain
higher levels of eight of 11 nutrients studied, including significantly greater
concentrations of the health-promoting polyphenols and antioxidants.
In this first comprehensive review of the scientific literature comparing nutrient
levels in organic and conventional food completed since 2003, a team of scientists
conclude that organically grown plant-based foods are 25% more nutrient dense,
on average, and hence deliver more essential nutrients per serving or calorie
consumed.
Nutrient levels were studied in 236 matched pairs of foods with scientifically
valid results on the levels of 10 nutrients, plus nitrates (high levels are
undesirable because of food safety risks). Each matched pair contains, for
example, an apple crop grown organically and another apple crop from a nearby
conventional farm with similar soils, climate, plant genetics, irrigation systems,
nitrogen levels, and harvest practices.
The new report is published as a "State of Science Review" by The
Organic Center and is entitled "New Evidence Confirms the Nutritional
Superiority of Plant-based Organic Foods." The co-authors are Charles
Benbrook, the Center's Chief Scientist, Xin Zhao of the University of Florida,
and three Washington State University (WSU) scientists Jaime Yanez, Neal Davies,
and Preston Andrews. Dr. Andrew Weil, a Center board member, wrote the "Foreword." The
full report and its executive summary are freely accessible on the Center's
website (
http://www.organic-center.org/science.nutri.php?action=view&report_id=126).
Selecting Scientifically Valid Studies
The team reviewed the study design and analytical methods used in 97 published,
peer-reviewed studies appearing since 1980. Earlier studies were excluded because
of the lack of clear, binding definitions of organic farming, changes in analytical
methods, and the recent recognition of the importance of antioxidant plant
phytonutrients. Studies before 1980 rarely reported data on total antioxidant
activity or total polyphenols.
Many of the 97 studies covered more than one crop or food. Out of a total of
135 study-crop combinations, 70% were deemed "acceptable" or "high
quality" based on a five-point screening system. Dr. Xin Zhao of the University
of Florida helped design the screening system in order to "assure the
organic and conventional crops were grown on the same type of soil, using similar
tillage and planting methods, the same plant variety, and well-defined and
established organic and conventional farming systems."
In addition, the team assured that the crops were picked at a comparable level
of maturity, handled the same way after harvest, and tested in the same form
using the same methods.
The 94 "acceptable" study-crop combinations were then reviewed for
the reliability of the analytical methods used to quantify nutrient levels.
On average, each study measured about ten nutrients using, on average, about
six methods (some methods are able to quantify levels of several nutrients).
Out of the approximate total 560 study-crop-method combinations, about 10%
(55) were deemed "invalid" based on the criteria established by the
team.
Team member Dr. Jaime Yanez of WSU emphasizes that "while analytical
methods have steadily improved over the years, we found that some recently
published high-profile papers utilized analytical methods that were ranked
'high quality,' while other methods in the same papers were 'invalid' based
on our explicit criteria."
Comparing Nutrient Levels
The team identified eight or more valid matched pairs for 10 nutrients, plus
nitrates including:
- Four measures of antioxidant activity;
- Precursors of three vitamins A, C and E;
- Two minerals (phosphorous and potassium);
- Nitrates (higher levels are undesirable), and
- Total protein.
There were 191 matched pairs in which the antioxidant, vitamin and mineral
levels were compared. The organic food was more nutrient dense in 119 of these
pairs, or 62%, compared to 36% of the conventional matched pairs with more
nutrients. There were no differences in 2% of the pairs.
The conventional samples contained modestly higher levels of protein in 85%
of 27 matched pairs (an advantage), but also much higher levels of nitrates
in 83% of 18 matched pairs (a nutritional and food safety disadvantage).
Matched pairs comparing potassium, phosphorous, and total protein accounted
for over 75% of the 87 matched pairs in which the conventional food was more
nutrient dense. In general, compared to vitamins and antioxidants, these three
nutrients are of less importance because they are present in the average American
diet at adequate to excessive levels.
The organic food was more nutrient dense in 75% of the matched pairs comparing
total antioxidant capacity, total polyphenols, and two key flavonoids, quercetin
and kaempferol. The typical American diet delivers barely half the recommended
levels of these important, health-promoting nutrients, which is, according
to co-author Dr. Benbrook, "a major reason why the federal government
recommended such a significant increase in the number of daily servings of
fruits and vegetables as part of the new USDA dietary guidelines that were
issued in 2005."
The report also describes some of the reasons rooted in plant physiology that
explain why several nutrients tend to rise or fall together in organic versus
conventional crops grown under comparable conditions. Co-author Dr. Preston
Andrews, an expert in horticultural plant growth and development at WSU, explains
that "In most well-designed comparison studies, we see marginally to markedly
elevated levels of Vitamin C, total phenolics, antioxidant activity, and certain
flavonoids in organic samples, coupled with generally lower levels of protein,
nitrates, and beta-carotene, the precursor of Vitamin A. In most cases the
explanation is rooted in the forms of nitrogen available to the plant and how
the plant responds to excessive levels of readily available nitrogen."
Magnitude of Differences Heavily Favors Organic Foods
Several methods were used to place the magnitude of the differences in nutrient
levels between organic and conventional foods into perspective. In two-thirds
of the matched pairs favoring the conventional food, the differences in favor
of conventional were under 10%, compared to 26% of the matched pairs in which
the organic food was more nutrient dense by a margin under 10%.
The premium in favor of the conventional food was 21% or greater in just 15%
of the matched pairs in which the conventional food was more nutrient dense,
whereas in the more nutrient dense organic food matched pairs, 41% favored
organic by 21% or more, and 24% of the pairs were 31% or more nutrient dense.
The largest differences were in the case of the flavonoid quercetin, where
the organic foods were 2.4-times more nutrient dense on average, and nitrates,
where levels were 1.8-fold lower in organic foods (a desirable nutritional
feature).
The consistency of the differences observed, the relative importance of the
nutrients for which the organic samples tended to be markedly higher, and the
sizable advantage in many of the organic foods within matched pairs lead the
team to conclude -
"Yes, organic plant-based foods are, on average, more nutritious in terms
of their nutrient density for compounds validated by this study's rigorous
methodology."
Commenting on the results, Dr. Neal Davies, a professor in the School of Pharmacology
at Washington State University, and a study co-author, said "We have carried
out many careful comparisons of both nutrient levels and biological activity
of antioxidant polyphenols in organic and conventional foods over the last
five years. Not only are we seeing a general trend in favor of the nutrient
density of organic food, but also evidence that nutrients are often present
in organic foods in a more biologically active form."
For More Information Contact:
Dr. Charles Benbrook, The Organic Center: cbenbrook@organic-center.org,
541-828-7918
Dr. Xin Zhao, University of Florida: zxin@ufl.edu
Dr. Jaime Yanez, WSU: jaimeayanez@gmail.com
Dr. Neal Davies, WSU: ndavies@wsu.edu
Dr. Preston Andrews, WSU: andrewsp@wsu.edu