Demand for organic foods is partially driven by consumers' perceptions that they are more nutritious. However, scientific opinion is divided on whether there are significant nutritional differences between organic and non-organic foods, and two recent reviews have concluded that there are no differences. In the present study, we carried out meta-analyses based on 343 peer-reviewed publications that indicate statistically significant and meaningful differences in composition between organic and non-organic crops/crop-based foods. Most importantly, the concentrations of a range of antioxidants such as polyphenolics were found to be substantially higher in organic crops/crop-based foods, with those of phenolic acids, flavanones, stilbenes, flavones, flavonols and anthocyanins being an estimated 19 (95 % CI 5, 33) %, 69 (95 % CI 13, 125) %, 28 (95 % CI 12, 44) %, 26 (95 % CI 3, 48) %, 50 (95 % CI 28, 72) % and 51 (95 % CI 17, 86) % higher, respectively. Many of these compounds have previously been linked to a reduced risk of chronic diseases, including CVD and neurodegenerative diseases and certain cancers, in dietary intervention and epidemiological studies. Additionally, the frequency of occurrence of pesticide residues was found to be four times higher in conventional crops, which also contained significantly higher concentrations of the toxic metal Cd. Significant differences were also detected for some other (e.g. minerals and vitamins) compounds. There is evidence that higher antioxidant concentrations and lower Cd concentrations are linked to specific agronomic practices (e.g. non-use of mineral N and P fertilisers, respectively) prescribed in organic farming systems. In conclusion, organic crops, on average, have higher concentrations of antioxidants, lower concentrations of Cd and a lower incidence of pesticide residues than the non-organic comparators across regions and production seasons.

Biotechnology and Food Research MTT Agrifood Research Finland FI 31600Jokioinen Finland

Center for Sustaining Agriculture and Natural Resources Washington State University Pullman WA USA

Department of Agricultural Sciences School of Agriculture and Veterinary Medicine University of Bologna Viale Fanin 42 40127Bologna Italy

Department of Animal Physiology Faculty of Biology University of Warsaw Miecznikowa 1 02 096Warsaw Poland

Department of Gene Bank Crop Research Institute Drnovská 507 73 161 06 Praha 6 Ruzyně Czech Republic

Department of Organic Farming and Food Technology Technological Educational Institute of Ionian Islands Iosif Momferatou and Ilia Miniati PC28100 Argostoli Cephalonia Greece

Department of Pesticide Control and Phytopharmacy Benaki Phytopathological Institute GR 14561 Kifissia Athens Greece

Faculty of Human Nutrition and Consumer Sciences Warsaw University of Life Sciences Nowoursynowska 159c 02 776Warsaw Poland

Human Nutrition Research Centre School of Agriculture Food and Rural Development Newcastle University Agriculture Building Kings Road Newcastle upon TyneNE1 7RU UK

INRA UR407 Pathologie végétale 67 allée des chênes F 84143Montfavet Cedex France

Research Institute of Organic Agriculture Ackerstrasse 113 CH 5070Frick Switzerland

School of Agriculture Food and Rural Development Newcastle University Nafferton Farm Stocksfield Northumberland NE43 7XD UK

School of Biology Newcastle University Ridley Building Newcastle upon TyneNE1 7RU UK

Comment In

Br J Nutr. 2014 Nov 28;112(10):1745-7. doi: 10.1017/S0007114514002645. PubMed

See more in PubMed

Yiridoe EK, Bonti-Ankomah S & Martin RC (2005) Comparison of consumer perceptions and preference toward organic versus conventionally produced foods: a review and update of the literature. Renew Agric Food Syst 20, 193–205

Oughton E & Ritson C (2007) Food consumers and organic agriculture. In Handbook of Organic Food Quality and Safety, pp. 74–94 [Cooper J, Niggli U and Leifert C, editors]. Cambridge, UK: Woodhouse Publishing Ltd

Willer H & Kilcher L (2011) The World of Organic Agriculture. Statistics and Emerging Trends 2011. FiBL-IFOAM Report. Bonn: IFOAM and Frick: FiBL

Baker BP, Benbrook CM, Groth E 3rd, et al. (2002) Pesticide residues in conventional, integrated pest management (IPM)-grown and organic foods: insights from three US data sets. Food Addit Contam 19, 427–446 PubMed

Lampkin NH (2002) Organic Farming, 2nd ed.Ipswich: Old Pond Publishing

Hansen AL (2010) The Organic Farming Manual: A Comprehensive Guide to Starting and Running a Certified Organic Farm. North Adams, MA: Storey Books

Cooper J, Sanderson R, Cakmak I, et al. (2011) Effect of organic and conventional crop rotation, fertilization, and crop protection practices on metal contents in wheat (Triticum aestivum). J Agric Food Chem 59, 4715–4724 PubMed

van Bueren ETL, Jones SS, Tamm L, et al. (2011) The need to breed crop varieties suitable for organic farming, using wheat, tomato and broccoli as examples: a review. NJAS Wageningen J Life Sci 58, 193–205

Tetard-Jones C, Edwards M, Rempelos L, et al. (2013) Effects of previous crop management, fertilization regime and water supply on potato tuber proteome and yield. Agronomy 3, 59–85

Rempelos L, Cooper J, Wilcockson S, et al. (2013) Quantitative proteomics to study the response of potato to contrasting fertilisation regimes. Mol Breed 31, 363–378

Lehesranta SJ, Koistinen KM, Massat N, et al. (2007) Effects of agricultural production systems and their components on protein profiles of potato tubers. Proteomics 7, 597–604 PubMed

Tetard-Jones C, Shotton PN, Rempelos L, et al. (2013) Quantitative proteomics to study the response of wheat to contrasting fertilisation regimes. Mol Breed 31, 379–393

van Dijk JP, Cankar K, Scheffer SJ, et al. (2009) Transcriptome analysis of potato tubers – effects of different agricultural practices. J Agric Food Chem 57, 1612–1623 PubMed

van Dijk JP, Leifert C, Barros E, et al. (2010) Gene expression profiling for food safety assessment: examples in potato and maize. Regul Toxicol Pharmacol 58, Suppl. 3, S21–S25 PubMed

van Dijk JP, Cankar K, Hendriksen PJM, et al. (2012) The identification and interpretation of differences in the transcriptomes of organically and conventionally grown potato tubers. J Agric Food Chem 60, 2090–2101 PubMed

Del Rio D, Rodriguez-Mateos A, Spencer JPE, et al. (2013) Dietary (poly)phenolics in human health: structures, bioavailability, and evidence of protective effects against chronic diseases. Antioxid Redox Signal 18, 1818–1892 PubMed PMC

Wahlqvist ML (2013) Antioxidant relevance to human health. Asia Pac J Clin Nutr 22, 171–176 PubMed

Fardet A (2010) New hypotheses for the health-protective mechanisms of whole-grain cereals: what is beyond fibre? Nutr Res Rev 23, 65–134 PubMed

Dangour AD, Dodhia SK, Hayter A, et al. (2009) Nutritional quality of organic foods: a systematic review. Am J Clin Nutr 90, 680–685 PubMed

Brandt K, Leifert C, Sanderson R, et al. (2011) Agroecosystem management and nutritional quality of plant foods: the case of organic fruits and vegetables. Crit Rev Plant Sci 30, 177–197

Smith-Spangler C, Brandeau ML, Hunter GE, et al. (2012) Are organic foods safer or healthier than conventional alternatives? A systematic review. Ann Intern Med 157, 348–366 PubMed

Benbrook C, Zhao X, Davies N, et al. (2008) New evidence confirms the nutritional superiority of plant-based organic foods. http://organic-center.org/reportfiles/NutrientContentReport.pdf (accessed June 2014)

Curl C, Fenske RA & Elgethun K (2003) Organophosphorus pesticide exposure of urban and suburban preschool children with organic and conventional diets. Environ Health Perspect 111, 377–382 PubMed PMC

Leifert C, Ball K, Volakakis N, et al. (2008) Control of enteric pathogens in ready-to-eat vegetable crops in organic and ‘low input’ production systems: a HACCP-based approach. J Appl Microbiol 105, 931–950 PubMed

Stewart G (2010) Meta-analysis in applied ecology. Biol Lett 6, 78–81 PubMed PMC

Koricheva J & Gurevitch J (2013) Place of meta-analysis among other methods of research synthesis. In Handbook of Meta-Analysis in Ecology and Evolution, [Koricheva J, Gurevitch J and Mengersen K, editors]. Princeton, NJ: Princeton University Press

Brandt K, Srednicka-Tober D, Baranski M, et al. (2013) Methods for comparing data across differently designed agronomic studies: examples of different meta-analysis methods used to compare relative composition of plant foods grown using organic or conventional production methods and a protocol for a systematic review. J Agric Food Chem 61, 7173–7180 PubMed

Stewart G, Cote I, Rothstein H, et al. (2013) First steps in beginning a meta-analysis. In Handbook of Meta-Analysis in Ecology and Evolution, pp. 27–36 [Koricheva J, Gurevitch J and Mengersen K, editors]. Princeton, NJ: Princeton University Press

Palupi E, Jayanegara A, Ploeger A, et al. (2012) Comparison of nutritional quality between conventional and organic dairy products: a meta-analysis. J Sci Food Agric 92, 2774–2781 PubMed

Anonymous (2013) The R Project for Statistical Computing http://www.r-project.org/ (accessed 10 February 2013)..

Viechtbauer W (2010) Conducting meta-analyses in R with the metafor package. J Stat Softw 36, 1–48

Hedges LV & Olkin I (1985) Statistical Methods for Meta-Analysis. San Diego, CA: Academic Press

Sanchez-Meca J & Marin-Martinez F (2010) Meta-analysis. In International Encyclopedia of Education, 3rd ed., pp. 274–282 [Peterson P, Baker E and McGaw B, editors]. Amsterdam: Elsevier

Lipsey MW & Wilson DB (editors) (2001) Practical Meta-analysis. Thousand Oaks, CA: Sage Publications

Hedges LV, Gurevitch J & Curtis PS (1999) The meta-analysis of response ratios in experimental ecology. Ecology 80, 1150–1156

Mengersen K, Schmidt C, Jennions M, et al. (2013) Statistical models and approaches to inference. In Handbook of Meta-Analysis in Ecology and Evolution, pp. 89–107 [Koricheva J, Gurevitch J and Mengersen K, editors]. Princeton, NJ: Princeton University Press

Rothstein HR, Sutton AJ & Borenstein M (2006) Publication Bias in Meta-Analysis. Chichester, UK: John Wiley & Sons Ltd

Gurevitch J & Hedges LV (1999) Statistical issues in ecological meta-analyses. Ecology 80, 1142–1149

Manly BFJ (1997) Randomization, Bootstrap and Monte Carlo Methods in Biology, 2nd ed.New York: Chapman & Hall

Rosenberg M, Rothstein H & Gurevitch J (2013) Effect sizes: conventional choices and calculations. In Handbook of Meta-Analysis in Ecology and Evolution, pp. 61–71 [Koricheva J, Gurevitch J and Mengersen K, editors]. Princeton, NJ: Princeton University Press

Guyatt GH, Oxman AD, Vist GE, et al. (2008) GRADE: an emerging consensus on rating quality of evidence and strength of recommendations. BMJ 336, 924–926 PubMed PMC

Grinder-Pedersen L, Rasmussen SE, Bügel S, et al. (2003) Effect of diets based on foods from conventional versus organic production on intake and excretion of flavonoids and markers of antioxidative defense in humans. J Agric Food Chem 51, 5671–5676 PubMed

Søltoft M, Bysted A, Madsen KH, et al. (2011) Effects of organic and conventional growth systems on the content of carotenoids in carrot roots, and on intake and plasma status of carotenoids in humans. J Sci Food Agric 91, 767–775 PubMed

Huber M, van de Vijver LPL, Parmentier H, et al. (2010) Effects of organically and conventionally produced feed on biomarkers of health in a chicken model. Br J Nutr 103, 663–676 PubMed

Lauridsen C, Yong C, Halekoh U, et al. (2008) Rats show differences in some biomarkers of health when eating diets based on ingredients produced with three different cultivation strategies. J Sci Food Agric 88, 720–732

Srednicka-Tober D, Baranski M, Gromadzka-Ostrowska J, et al. (2013) Effect of crop protection and fertilization regimes used in organic and conventional production systems on feed composition and physiological parameters in rats. J Agric Food Chem 61, 1017–1029 PubMed

Nicholson RL & Hammerschmidt R (1992) Phenolic compounds and their role in disease resistance. Annu Rev Phytopathol 30, 369–389

Bennett RN & Wallsgrove RM (1994) Secondary metabolites in plant defense mechanisms. New Phytol 127, 617–633 PubMed

Almuayrifi M (2013) Effect of fertilisation, crop protection, pre-crop and variety choice on yield of phenols content diseases severity and yield of winter wheat. PhD Thesis, Newcastle University.

Sander JF & Heitefuss R (1998) Susceptibility to Erysiphe graminis f. sp. tritici and phenolic acid content of wheat as influenced by different levels of nitrogen fertilization. J Phytopathol 146, 495–507

Rühmann S, Leser C, Bannert M, et al. (2002) Relationship between growth, secondary metabolism, and resistance of apple. Plant Biol 4, 137–143

Stewart AJ, Chapman W, Jenkins GI, et al. (2001) The effect of nitrogen and phosphorus deficiency on flavonol accumulation in plant tissues. Plant Cell Environ 24, 1189–1197

European Commission (2008) Commission Regulation (EC) No. 629/2008 of 2 July 2008 amending Regulation (EC) No. 1881/2006 setting maximum levels for certain contaminants in foodstuffs. Off J Eur Union L173, 6–9

Bešter PK, Lobnik F, Eržen I, et al. (2013) Prediction of cadmium concentration in selected home-produced vegetables. Ecotoxicol Environ Saf 96, 182–190 PubMed

European Commission (2005) Commission Regulation (EC) No. 396/2005 of 23 February 2005 on maximum residue levels of pesticides in or on food and feed of plant and animal origin and amending Council Directive 91/414/EEC. Off J Eur Union L70, 1–16

European Food Safety Authority (2013) Maximum Residue Levels http://www.efsa.europa.eu/en/pesticides/mrls.htm (accessed accessed September 2013).

European Food Safety Authority (2011) The 2009 European Union report on pesticide residues in food. EFSA 9, 2430 PubMed

Marinovich M, Ghilardi F & Galli CL (1996) Effect of pesticide mixtures on in vitro nervous cells: comparison with single pesticides. Toxicology 108, 201–206 PubMed

Pape-Lindstrom PA & Lydy MJ (1997) Synergistic toxicity of atrazine and organophosphate insecticides contravenes the response addition mixture model. Environ Toxicol Chem 16, 2415–2420

Axelrad JC, Howard CV & McLean WG (2002) Interactions between pesticides and components of pesticide formulations in an in vitro neurotoxicity test. Toxicology 173, 259–268 PubMed

Lueck L, Schmidt C, Cooper J, et al. (2006) Effect of organic, low-input and conventional production systems on yield and quality of winter wheat. Aspects Appl Biol 80, 135–140

Bilsborrow P, Cooper J, Tetard-Jones C, et al. (2013) The effect of organic and conventional crop production systems on the yield and quality of wheat (Triticum aestivum) grown in a long-term field trial. Eur J Agron 51, 71–80

Cordain L, Eaton SB, Sebastian A, et al. (2005) Origins and evolution of the Western diet: health implications for the 21st century. Am J Clin Nutr 81, 341–354 PubMed

Astrup A (2005) The satiating power of protein – a key to obesity prevention? Am J Clin Nutr 82, 1–2 PubMed

McKnight GM, Duncan CW, Leifert C, et al. (1999) Dietary nitrate in man: friend or foe? Br J Nutr 81, 349–358 PubMed

Lundberg JO, Weitzberg E & Gladwin MT (2008) The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics. Nat Rev Drug Discov 7, 156–167 PubMed

Machha A & Schechter AN (2012) Inorganic nitrate: a major player in the cardiovascular health benefits of vegetables? Nutr Rev 70, 367–372 PubMed PMC

Organic Food Consumption and Risk of Obesity: A Systematic Review and Meta-Analysis

Feed Composition Differences Resulting from Organic and Conventional Farming Practices Affect Physiological Parameters in Wistar Rats-Results from a Factorial, Two-Generation Dietary Intervention Trial