The production of organic food requires special considerations (Figure 2). Generally, organic farming is solely grounded in biological and ecological processes that mitigate the environmental impact of agricultural practices while preserving the natural qualities of food ^[10][23][10,24]. In this holistic approach, pest and disease control are achieved naturally, eliminating the need for synthetic chemicals utilized in conventional farming ^[23][24][24,25]. Additionally, organic food must not be sourced from genetically modified organisms (GMOs) ^[23][25][24,26]. Organic farming also relies on mechanical weeding as an alternative to traditional herbicide input, potentially leading to increased weed cover that benefits various organisms by promoting biodiversity ^[25][26]. Core principles of organic agriculture, such as the use of green manure, crop diversification, and small fields, further contribute to the production system’s sustainability ^[25][26]. Following these principles, organic farming is believed to enhance soil fertility and foster biodiversity. Studies indicate that local species richness and abundance can increase by approximately 34% and 50%, respectively, across various crops worldwide compared to conventional farming practices ^[25][26]. Thus, there has been a recent upsurge in both the production and purchasing of organic goods, driven by a heightened demand for natural products that undergo minimal processing and abstain from synthetic and artificial fertilizers or pesticides in their production processes ^[26][27][27,28].

Unlike conventional farming, organic farming does not use genetic engineering or synthetic pesticides in the food production process, allowing for an assessment of their health effects. The use of genetic engineering and GMOs can pose various health risks, such as allergic reactions and unexpected interlinks between genes due to gene additions and modifications ^[28][31]. Moreover, pesticides utilized in agriculture can accumulate in soil and water, quickly entering the food chain and impacting human health ^[29][32]. These health effects span from allergic reactions to lung damage, causing breathing difficulties, nervous system problems, birth defects, and the risk of chronic diseases such as cancer ^[29][32]. For instance, the organochlorine insecticide (OCI) dichlorodiphenyltrichloroethane (DDT) functions by opening sodium channels in the human nervous system, leading to increased firing of action potentials that can result in spasms and, in severe cases, death ^[30][31][34,35]. Conversely, carbamate insecticides inhibit the acetylcholinesterase enzyme, interfering with cell replication and differentiation, proper synapse signaling, and other neurotoxic effects ^[30][32][34,36]. Furthermore, the growth regulator herbicide 2,4-D, used to eliminate weeds, has been linked to severe eye irritations and fertility problems in men ^[30][34]. Studies have also associated anilide/aniline herbicides with risks of colon and rectal cancer ^[30][34]. Glyphosate, a common ingredient in pesticides found in GM crops, has also been linked to cancer risks, especially non-Hodgkin lymphoma (NHL) ^[28][31]. Glyphosate was first used as a broad-spectrum pesticide in 1974 ^[33][37]. As genetically engineered glyphosate-tolerant crops were introduced, glyphosate quickly spread worldwide and has now become the most widely used pesticide in agricultural and residential sectors ^[33][37]. However, glyphosate is an organophosphorus compound which interferes with aromatic amino acid synthesis through a mechanism unique to plants ^[33][37]. Thus, concerns have arisen about glyphosate’s potential genotoxicity through the induction of oxidative stress for human cells in vitro and in animal experiments ^[33][37].

It is important to note that a majority of these experiments tested much higher doses than those permitted for agricultural use. Notably, esteemed institutions such as the Food and Agriculture Organization (FAO), the European Chemicals Agency (ECHA) and the European Food Safety Authority (EFSA) have affirmed glyphosate’s status as non-toxic and non-carcinogenic to human target organs as of 2022 ^[34][38]. In rabbit studies conducted by the EFSA, an acceptable daily intake (ADI) of 0.5 mg/kg of body weight per day was defined, while the FAO and WHO established an acute toxicity measure (LD50) of 5600 mg/kg of body weight for the oral pathway and over 2000 mg/kg of body weight for the dermal pathway ^[34][38]. Consequently, the commercialization of glyphosate-based herbicides (GBHs) is subject to stringent regulations, including the establishment of maximum residue limits (MRLs) for glyphosate residues in various food items.

Considering the MRL for pesticides is typically determined through testing individual pesticides on rats for a relatively brief duration, there is a substantial lack of knowledge regarding the consequences of consuming potentially hundreds of different pesticides over one’s lifetime. The intricate interplay of these various pesticides remains largely unknown. Thus, further research is needed to uncover the cumulative long-term health effects of glyphosate and other pesticide residues, as many studies reveal a variety of toxic effects ^[34][38]. As a result, pesticide use may adversely affect human cells through mechanisms still unclear, and it may be possible to minimize these health risks by re-orienting agricultural practices toward more organic approaches.

The nutrient and mineral content of crops is affected by various agronomic factors including fertilization type, crop rotation designs and crop protection protocols ^[23][35][24,39]. For example, the addition of organic matter to soil helps provide food for beneficial plant microorganisms, and in return, these stimulated microorganisms produce valuable compounds (including citrate and lactate) that make soil minerals more available to organic plant roots ^[35][39]. In addition, organic farming allows for the slow release of soil minerals over time, causing essential nutrients to become available when needed, whereas chemical fertilizers quickly dissolve in irrigation water and deliver excess quantities of nutrients to crops, often past what is needed ^[35][39]. Thus, agronomic differences in organic versus conventional farming systems may impact the quantity and quality of beneficial compounds that can be obtained from each crop type ^[23][35][24,39]. However, studies comparing the nutrient content between organic and conventional crops have revealed inconsistent results ^[23][24]. Further on, many of these studies lack the necessary control factors to validate the results, such as failing to consider the different environmental and growing conditions that affect crop quality ^[23][24]. In 2012, Smith-Spangler et al. ^[36][29] reviewed the results of 223 studies examining the nutrient content of organic foods, including ascorbic acid, phosphorus, calcium, magnesium, iron and various vitamins. The findings showed that organic fruits, vegetables, and grains do not exhibit significantly higher nutrient levels compared with their non-organic counterparts. However, organic produce did show higher levels of phosphorus when compared with non-organic produce ^[36][29]. All in all, the evidence was not strong enough to suggest that organic foods are more nutritious than non-organic foods. However, further recent experiments ^{[37][38][39][40]}[40,41,42,43] have demonstrated that some organic foods, such as corn grain, wheat flour, broccoli, tomato, black sesame and leafy vegetables, contain more minerals and vitamins, which are discussed below.

The most essential minerals are calcium, magnesium, potassium, iron, zinc, copper, manganese, selenium and iodine ^[37][40]. Studies have shown that the content of these minerals in fruits, especially apples, does not differ significantly between organically grown and conventional methods ^[37][38][40,41]. Studies on organic vegetables, however, revealed higher levels of iron and magnesium compared to conventionally grown vegetables. Overall, Worthington revealed that the iron and magnesium content in organic crops was higher by 21% and 29%, respectively ^[35][39]. Moreover, a study by Yu et al. ^[39][42] demonstrated 20% higher magnesium content and 30% higher phosphorus and potassium contents in organic compared to conventionally grown summer corn. However, the study did not provide details on methodologies or sample sizes, thereby limiting the credibility of the reported data. They also found higher levels of zinc and iron in organic corn, but this increase was not significant ^[39][42]. These findings were further compounded by Rembialkowska ^[40][43], where the results of many experiments demonstrated a higher level of iron, phosphorous and magnesium content in organically grown compared to non-organically grown products. These results may be attributed to the effects of traditional potassium fertilizers used in conventional agriculture, which can decrease the amount of magnesium—and consequently, phosphorus—absorbed from soils ^[35][39]. Further on, organic fertilizers tend to increase the number of soil microorganisms that affect various components of plant nutrient acquisition and metabolism, which may play an essential role in making iron more bioavailable to plant roots ^[35][39]. Confounding factors, including variations in soil fertility, pH levels and the presence of specific minerals across different plots and geographical regions, can significantly influence the absorption and availability of nutrients for plants ^[35][39]. Consequently, any observed differences in the nutritional content of organic and conventional produce may be attributed to variations in soil conditions and cultivation practices rather than the farming methods alone. To mitigate these potential confounding variables, researchers must meticulously control and monitor soil conditions, cultivation practices and climatic variations in their study to ensure that the comparison between organic and conventional crops is not influenced by any disparities in these factors.

Experiments on the various vitamin contents of different organic versus non-organic fruits and vegetables are limited. A 2010 review on the nutritional quality of organic food revealed higher vitamin C contents in organic potatoes, tomatoes, kale and celeriac as well as higher vitamin E content in organic olive oil ^[37][40]. Similarly, Worthington’s experiment revealed 27% higher vitamin C levels in organically grown lettuce, spinach, potatoes and cabbage ^[35][39]. On the other hand, some studies on beta-carotene (vitamin A precursor) have shown that the beta-carotene content of organic foods greatly depends on the type of fertilizer used, as nitrogen fertilizers have been shown to yield higher beta-carotene levels in carrots ^[37][38][40,41]. Other experiments have shown similar outcomes in conventional agriculture, such that increased fertilization changes the content of secondary plant metabolites ^[41][44]. For example, Mozafar ^[42][45] revealed that nitrogen fertilizer used in conventional fruits and vegetables could increase the amount of beta-carotene and reduce vitamin C levels. This phenomenon can be attributed to alterations in plant metabolism observed in response to the differences between organic and conventional fertilizers. For example, when exposed to a high influx of nitrogen, plants tend to increase protein production while diminishing carbohydrate production, ultimately leading to a reduction in vitamin C synthesis ^[35][39]. Consequently, the vitamin content in crops is significantly influenced by the specific agronomic factors associated with each farming system.

Oxidation of phenolic compounds by the polyphenol oxidase (PPO) enzyme is part of the plant antioxidant defense mechanism (to repair injuries on their surface). Phenolic compounds act as a chemical barrier against invading pathogens. Intact antioxidant defense in plants has been shown to have important implications for human health, including playing an anticarcinogenic role ^[39][42]. Organic cultivation operations have been revealed to increase the polyphenol content of peaches and pears as compared with their conventional counterparts [9]. Moreover, increased activity of the PPO enzyme towards chlorogenic and caffeic acids (antioxidant agents) was observed to be notably higher in the organic samples of peaches and pears [9]. Overall, various studies on organic crops have observed between 18% and 69% increased antioxidant activity in these products ^[43][46]. Intake of antioxidants and phenolic compounds from food consumption is important because these compounds have been shown to effectively reduce the risk of chronic diseases, including some neurodegenerative and cardiovascular diseases and cancer ^[43][46].

Importantly, organic foods also demonstrated lower levels of toxic metabolites, such as cadmium and pesticide residues ^[44][49]. Cadmium is a heavy metal that is known to accumulate in the body and exert toxic effects on the kidneys and liver ^[44][49]. Importantly, eight meta-analyses conducted by Barański et al. revealed that organic crops contained on average 48% lower cadmium concentrations than conventional crops ^[44][49]. Further on, the frequency of detectable pesticide residues was four times lower in organic crops, whereas the frequency of phenolic (antioxidant) compounds was on average 20–40% and, in some cases, over 60% higher in organic crops ^[44][49]. The study analyzed a comprehensive dataset comprising 343 peer-reviewed publications, where notable discrepancies emerged across different crop types, crop species, and studies conducted in countries with different climates, soil types and agronomic backgrounds. Thus, potential limitations of these meta-analyses include variations in study methodologies and geographical locations that confound the observed results. However, by employing the GRADE (Grading of Recommendations, Assessments, Development, and Evaluation) assessment to gauge the strength of evidence for a standard weighted meta-analysis, the overall strength of evidence was deemed moderate or high for the majority of parameters where significant differences were identified (i.e., many phenolic compounds, cadmium and pesticide residues) ^[44][49].

Accordingly, a French BioNutriNet case-control study investigated the difference in urinary pesticide metabolite concentrations between 150 high-organic-food consumers and 150 low-organic-food consumers, matched for dietary patterns and other relevant traits ^[45][50]. Notably, the authors saw significant reductions of organophosphrous pesticides (OPs), diethyl-thiophosphates, dimethylthiophosphase, dialkylphosphates (DAPs) and free 3-phenoxybenzoic acid in the high-organic-consumer group, ranging from –17% to –55% reductions compared to the low-consumption group ^[45][50]. These differences were attributed to fertilization techniques, crop protection regimens, and other agronomic factors between growing practices. For example, organic farming systems avoid the use of fertilizers produced from industrial waste, which are often the most contaminated by toxic heavy metals ^[35][39].

The findings from clinical experiments assessing the health impact of organic food on humans are relatively limited compared to other nutritional epidemiological studies. Many of these experiments are short term and may be confounded by variations in dietary patterns and lifestyles that profoundly affect human health ^[46][51]. Notably, observational studies often lack a comprehensive examination of the various health factors that may differ between organic and non-organic food consumers, such as lifestyle choices, physical activity levels and overall dietary patterns ^[45][46][50,51]. These factors may be a source of confounding that significantly influence the health outcomes observed, precipitating the need for further longitudinal intervention studies. Nevertheless, the compounds found in organic fruits and vegetables are generally believed to promote human health and longevity ^[46][51]. Consequently, individuals who consistently consume organic food often opt for more fruits and vegetables and less meat, potentially reducing the risk of mortality and chronic diseases ^{[47][48][49][50][51][52]}[52,53,54,55,56,57]. Additionally, research indicates that those who regularly choose organic food are more likely to be female, have higher education and income levels and maintain a healthier lifestyle by smoking less and engaging in more physical activity ^{[45][46][53][54]}[50,51,58,59]. As a result, the dietary compositions of organic and non-organic consumers may significantly differ.