6
Proceedings of the Nutrition Society (2002), 61, 19–24 DOI:10.1079/PNS2001126 © The Author 2002 Corresponding author: Professor C. M. Williams, fax +44 1189 318703, email [email protected] CAB InternationalPNSProceedings of Nutrition Society (2002)0029-651© Nutrition Society 2002 611 PNS 126C. M. WilliamsNutritional aspects of food safety19 24 6© Nutrition Society 2002 Nutritional quality of organic food: shades of grey or shades of green? Christine M. Williams Hugh Sinclair Unit of Human Nutrition, School of Food Biosciences, University of Reading, Reading RG6 6AP, UK Professor C. M. Williams, fax +44 1189 318703, email [email protected] Consumer concern regarding possible adverse health effects of foods produced using intensive farming methods has led to considerable interest in the health benefits of organically-produced crops and animal products. There appears to be widespread perception amongst consumers that such methods result in foods of higher nutritional quality. The present review concludes that evidence that can support or refute such perception is not available in the scientific literature. A limited number of studies have compared the nutrient compositions of organically- and conventionally-produced crops, with a very small number of studies that have compared animal products (meat, milk and dairy products) produced under the two agricultural systems. Very few compositional differences have been reported, although there are reasonably consistent findings for higher nitrate and lower vitamin C contents of conventionally-produced vegetables, particularly leafy vegetables. Data concerning possible impacts on animal and human health of diets comprising organic or conventional produce are extremely sparse. Data from controlled studies in animal models, particularly within single species, are limited or poorly designed, and findings from these studies provide conflicting conclusions. There are no reports in the literature of controlled intervention studies in human subjects. Comparison of health outcomes in populations that habitually consume organically- or conventionally-produced foods are flawed by the large number of confounding factors that might contribute to any differences reported. If consumer perceptions regarding potential health benefits of organic foods are to be supported, more research of better quality is needed than that which is currently available. Organic foods: Nutritional quality: Scientific studies Organic food is derived from crops or animals produced in a farming system that avoids the use of man-made fertilisers, pesticides, growth regulators and livestock feed additives (Institute of Food Science and Technology, 1999). Organic farming systems rely on crop rotation, animal and plant manures, some hand weeding and biological pest control. Although the organic farming movement in the UK dates back to the Second World War (Daldy, 1940), there has been a marked increase in the demand for organic foods over the past 5–10 years, with consequent growth of this niche market. At least in part, this demand appears to reflect consumer concern regarding the safety of food produced under intensive farming systems. A recent House of Lords Select Committee on European Communities (1999) report concluded that healthiness is a prime factor contributing to the willingness of the public to pay premium prices for organic food. In the UK MORI (Wright, 1997) reported that 60 % of the population would choose organic food if it was easily available and cost no more than conventional food. Despite the widespread conviction held by the public that organic food is ‘healthier’ than foods produced using conventional farming, evidence to support this perception is difficult to identify. This difficulty arises because very limited research has been conducted and much of the available scientific data is out-dated or based on inadequate study designs. The view that organic foods are ‘healthier’ than conventionally-produced foods appears to be based on the perception that organic foods have superior sensory attributes, contain lower levels of pesticides and synthetic fertilisers and have higher levels of nutrients and protective phytochemicals. Conversely, it has also been suggested that application of manure and reduced use of fungicides and antibiotics in organic farming could result in a greater contamination of organic foods by micro- organisms or microbial products. These wider food safety and quality aspects have recently been reviewed elsewhere (Tinker, 2001). The present review will confine itself to

Nutritional quality of organic food: shades of grey or shades of green?

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Page 1: Nutritional quality of organic food: shades of grey or shades of green?

Proceedings of the Nutrition Society (2002), 61, 19–24 DOI:10.1079/PNS2001126© The Author 2002

Corresponding author: Professor C. M. Williams, fax +44 1189 318703, email [email protected]

CAB InternationalPNSProceedings of Nutrition Society (2002)0029-651© Nutrition Society 2002 611PNS 126C. M. WilliamsNutritional aspects of food safety19246© Nutrition Society 2002

Nutritional quality of organic food: shades of grey or shades of green?

Christine M. WilliamsHugh Sinclair Unit of Human Nutrition, School of Food Biosciences, University of Reading, Reading RG6 6AP, UK

Professor C. M. Williams, fax +44 1189 318703, email [email protected]

Consumer concern regarding possible adverse health effects of foods produced using intensivefarming methods has led to considerable interest in the health benefits of organically-producedcrops and animal products. There appears to be widespread perception amongst consumers thatsuch methods result in foods of higher nutritional quality. The present review concludes thatevidence that can support or refute such perception is not available in the scientific literature. Alimited number of studies have compared the nutrient compositions of organically- andconventionally-produced crops, with a very small number of studies that have compared animalproducts (meat, milk and dairy products) produced under the two agricultural systems. Very fewcompositional differences have been reported, although there are reasonably consistent findingsfor higher nitrate and lower vitamin C contents of conventionally-produced vegetables,particularly leafy vegetables. Data concerning possible impacts on animal and human health ofdiets comprising organic or conventional produce are extremely sparse. Data from controlledstudies in animal models, particularly within single species, are limited or poorly designed, andfindings from these studies provide conflicting conclusions. There are no reports in the literatureof controlled intervention studies in human subjects. Comparison of health outcomes inpopulations that habitually consume organically- or conventionally-produced foods are flawed bythe large number of confounding factors that might contribute to any differences reported. Ifconsumer perceptions regarding potential health benefits of organic foods are to be supported,more research of better quality is needed than that which is currently available.

Organic foods: Nutritional quality: Scientific studies

Organic food is derived from crops or animals produced in afarming system that avoids the use of man-made fertilisers,pesticides, growth regulators and livestock feed additives(Institute of Food Science and Technology, 1999). Organicfarming systems rely on crop rotation, animal and plantmanures, some hand weeding and biological pest control.Although the organic farming movement in the UK datesback to the Second World War (Daldy, 1940), there hasbeen a marked increase in the demand for organic foodsover the past 5–10 years, with consequent growth of thisniche market. At least in part, this demand appears to reflectconsumer concern regarding the safety of food producedunder intensive farming systems. A recent House of LordsSelect Committee on European Communities (1999) reportconcluded that healthiness is a prime factor contributing tothe willingness of the public to pay premium prices fororganic food. In the UK MORI (Wright, 1997) reported that60 % of the population would choose organic food if it waseasily available and cost no more than conventional food.

Despite the widespread conviction held by the public thatorganic food is ‘healthier’ than foods produced usingconventional farming, evidence to support this perception isdifficult to identify. This difficulty arises because verylimited research has been conducted and much of theavailable scientific data is out-dated or based on inadequatestudy designs.

The view that organic foods are ‘healthier’ thanconventionally-produced foods appears to be based on theperception that organic foods have superior sensoryattributes, contain lower levels of pesticides and syntheticfertilisers and have higher levels of nutrients andprotective phytochemicals. Conversely, it has also beensuggested that application of manure and reduced use offungicides and antibiotics in organic farming could resultin a greater contamination of organic foods by micro-organisms or microbial products. These wider food safetyand quality aspects have recently been reviewed elsewhere(Tinker, 2001). The present review will confine itself to

Page 2: Nutritional quality of organic food: shades of grey or shades of green?

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Page 3: Nutritional quality of organic food: shades of grey or shades of green?

Nutritional aspects of food safety 21

data were for nitrate levels which were higher, and vitaminC levels which were lower, in conventional producecompared with organic produce. Twenty-five of forty-onestudies showed higher levels of nitrate and twenty-one ofthirty-six studies showed lower levels of vitamin C. Datawere insufficient or inconclusive for most of the othervitamins analysed. In the case of minerals and traceelements levels found in organic produce tended to be eitherhigher or the same as in conventional produce, with fewstudies showing lower levels in vegetables of organic origin(Table 1).

Lampkin’s (1990) review, which concluded favourablyon the benefits of organic production, is less critical of thelimited nature of the available data than those of Woeseet al. (1997) and Worthington (1998), and does notadequately address the scientific limitations of the compar-ative studies conducted to date. His review, as well as that ofWoese et al. (1997), refers to the use of ‘photon emissionmeasurements’ to compare the quality of organic andconventionally-produced foods. This method appears tomeasure the intensity of light energy emitted by plant cells.A number of studies conducted at the Elm Farm ResearchCentre, Newbury, Berks., UK (Elm Farm Research Centre,1989), have used this method to demonstrate that organi-cally-produced foods (e.g. carrots, onions) show higherphoton emission than conventional produce. However,despite the claimed scientific credibility of this approach, itwould undoubtedly be questioned with respect to its validityas a means of quantifying the nutritional quality of food. Astatement made to support the relevance of photon emissionfindings reads: ‘The higher level of light energy that a cellemits the greater its vitality and the potential for transfer ofits energy to the individual that consumes it.’ This statementand also one which refers to DNA ‘as the source of lightenergy in plants’, has no basis in science and does notaccord with currently-accepted concepts of cell, food andhuman energy metabolism. In contrast, it is disappointing tonote the complete lack of comparative studies of levels ofplant phytochemicals in organic v. conventionally-grownproduce. The considerable interest in potential protectivehealth effects of non-nutrient components of foods,including flavonoids, phyto-oestrogens and glucosinolates,suggests a potent mechanism by which the two growing

systems could yield plants of varying nutritional quality.Many of these components are produced by plants as stressresponses or protective mechanisms against harmful pests oradverse growing conditions. It might therefore be expectedthat growing systems that differ considerably with respect toplant exposure to stressed conditions would lead to differ-ences in the contents of these potentially-protectivecompounds. Future research in this area is not onlywarranted, but essential if credible scientific data that cansupport the possibility of enhanced nutritional properties oforganic crops is to be provided to consumers.

Although there are serious limitations in the quantity andquality of the data described earlier, the reviews of bothWoese et al. (1997) and Worthington (1998) show a trendfor organic produce to have a higher nutrient content thanconventional produce. However, although the weight ofevidence at the present time is suggestive of higher nutrientquality of organic produce, this finding does not seem toapply to all nutrients or all crops, and further research ofbetter quality than that currently available is needed toconfirm these tentative conclusions. Some data may beexplicable in terms of the reported higher water content ofconventional crops. However, if this finding represents themajor explanation, then a more consistent effect on levels ofall the nutrients would be expected to be seen. The mostconsistent data are those available for vitamin C and nitrate,which support beneficial effects of organic production onlevels of these nutrients.

Effects of agricultural methods on animal health

Few controlled intervention studies have compared effectsof organic and conventionally-grown feeds on animalhealth in the long term, and many of the studies reported inthe literature are extremely dated. Indeed, some of thestudies were originally conducted in the 1920s and 1930sby scientists investigating ‘essential growth factors’ orvitamins. The early work of McCarrison (1926) showedthat doves fed a supplement of millet grown using differenttypes of fertiliser showed marked differences in weight gainover a period of 2 months. The best growth performancewas seen in doves fed millet grown under cattle manure,whilst millet grown under mineral fertiliser supported muchlower growth rates. Table 2 summarises studies conductedbetween 1926 and 1992 that have assessed either weight orreproductive performance of rodents or rabbits fed organicor conventionally-grown feed. As in the case of the nutrientcomposition data, caution should be used in placingexcessive reliance on the findings, some of which havebeen published only in the form of results from disser-tations. Insufficient data is available to present summarytables for species other than rodents and rabbits. Repro-ductive performance is generally considered a robustenvironmental health indicator because it is less affected bygenetic determinants than other outcomes.

Only one study (Scheunert et al. 1934) observed worseperformance in organically-fed animals (rats), althoughScott et al. (1960) showed mice fed a mixed organic andconventional feed had poorer reproductive performancethan those raised either on conventional or organic feedalone. A majority of the studies found that animals given

Table 1. Comparison of protein, nitrate and selected vitamin andmineral contents of organic v. conventionally-grown crops (derived

from Worthington, 1998)

Nutrient Increased Same Decreased

Protein qualityNitrateVitamin Cβ-caroteneB vitaminsCaMgFeZn

35

2152

211715

4

01012

512202414

9

025

3326463

(No. of studies of organic crops shown to have increased, decreasedor same nutrient content compared with conventionally-growncrops)

Page 4: Nutritional quality of organic food: shades of grey or shades of green?

22 C. M. Williams

organic feed fared better than those fed conventional feed.However, there is little internal consistency, even amongstthe studies that have shown beneficial findings. Whereassome of the earlier studies in rabbits found clear evidencefor reduced egg production and abnormal histology inconventionally-fed animals (Hahn et al. 1971; Aehnelt &Hahn, 1973), other studies did not (Bram, 1974; Alter 1978;Meinecke, 1982). One of the criticisms of the earlier studiesis that the nutrient compositions of the diets were frequentlydifferent between the two groups. Recent studies haveprovided more rigorously-controlled nutrient conditions(Gottschewski, 1975; Edelmuller, 1984; Staiger, 1986).However, even these studies have not demonstratedconcordant findings, with some of the studies showinghigher pregnancy and birth rates (Staiger, 1986), whereas inother studies beneficial effects of organic feeds on numbersof live births were the dominant findings (Edelmuller,1984). The more recent studies in rodents have also tendedto observe greatest effects on numbers of stillborn animalsand on perinatal mortality (Neudecker, 1987; Velimirovet al. 1992).

Based on the data available from controlled animalfeeding studies, there appears to be modest evidence tosuggest that organic feed may have beneficial effects onanimal health, particularly with respect to reproduction andpregnancy outcome. However, the small number of studies,the variability in the study designs and the dated nature ofmuch of the animal work suggests conclusions cannot bedrawn at the present time. The lack of internal consistencyin the data is of particular concern. Furthermore, it is not atall clear from these studies whether any differences in repro-ductive performance that might exist can be attributed todifferences in nutritional status of the animals, or whetherthe data reflect adverse effects of pesticide residues or otherchemicals. The very small differences in nutrient contents ofcrops grown under the two systems that were discussedearlier (p. 20) would be very unlikely to provide a nutri-tional basis for the differences in reproductive performancein these animals.

Effects of agricultural methods on human health

There have been no post-war controlled studies that havecompared effects of organic and conventional products onhuman health; such studies pose considerable problems offeasibility, cost and ethics. They would need to be carriedout under very carefully controlled conditions over longperiods of time, thereby limiting the number and type ofsubjects who would be eligible and available for study. Afew observational studies of sperm quality in organic andnon-organic farmers have been published, with one studyshowing lower semen counts in conventional farmers thanorganic farmers and the other study showing no differencebetween the two groups (Jensen et al. 1996; Juhler et al.1999). A few experiments conducted in Germany in the1930s and 1940s compared effects on human health of foodsproduced using either organic or mixed (organic pluschemical) fertilisers. No effects were observed in experi-ments involving 260 adolescents (Wendt, 1943) or 300adults (Reiter et al. 1938). In later studies crops grown withmixed fertilisers were found to have more β-carotene andminerals but lower levels of B vitamins than crops grownorganically. No effects of these products on blood variableswere observed in adults, although in infants there was ahigher daily growth rate and higher serum β-carotene inchildren fed on crops grown under mixed fertiliserconditions (Dost & Schupan, 1944; Schupan, 1972). Lack ofrelevant dietary data, heterogeneity in the study populationsand limited information on growing conditions of the foodsused means that much of this early data cannot bescrutinised according to current scientific criteria. For thisreason no valuable inferences or interpretations can bederived from these studies.

Conclusions

There have been very few scientific studies in which foodsgrown conventionally have been compared, undercomparable and controlled conditions, with those producedorganically, in terms of their nutrient composition or their

Table 2. Comparison of weight gain and reproductive performance in rodents and rabbits fed organic or conventionally-grown feed

Species Study Animals fed organic feeds showed:

Rats and mice

Rabbits

McCarrison (1926)Rowlands & Wilkinson (1930)Scheunert et al. (1934)Miller & Dema (1958)Scott et al. (1960)

McSheehy (1977)Neudecker (1987), Velimirov et al. (1992)

Hahn et al. (1971), Aehnelt & Hahn (1973),Aehnelt & Hahn (1978)

Bram (1974), Alter (1978), Meinecke (1982)Gottschewski (1975)Staiger (1986)Edelmuller (1984)

Greater weight gainSuperior weight gainShorter lifespan, worse healthNo difference in weight gain or reproductionBetter reproduction with organic feeds; worst performance with mixed

organic and conventional feedNo difference in weaning weightNo differences in gestation rate, litter weight or weaning weight. Lower

stillborn and perinatal mortalityGreater no. of eggs, higher fertilisation rate, beneficial histological changes

in female genital organsNo differences in reproductive performance, ovaries, uterusLower mortality of newbornLong-term fertility rate (three generations) higherMore young born alive

Page 5: Nutritional quality of organic food: shades of grey or shades of green?

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Page 6: Nutritional quality of organic food: shades of grey or shades of green?

24 C. M. Williams

Worthington V (1998) Effect of agricultural methods on nutritionalquality: a comparison of organic with conventional crops.Alternative Therapies 4, 58–68.

Wright S (1997) Europe goes organic. Food Ingredients Europe 3,39–43.