GM crops and the rat digestive tract: A critical review

Abstract

The aim of this review is to examine the relationship between genetically modified (GM) crops and health, based on histopathological investigations of the digestive tract in rats. We reviewed published long-term feeding studies of crops containing one or more of three specific traits: herbicide tolerance via the EPSPS gene and insect resistance via cry1Ab or cry3Bb1 genes. These genes are commonly found in commercialised GM crops. Our search found 21 studies for nine (19%) out of the 47 crops approved for human and/or animal consumption. We could find no studies on the other 38 (81%) approved crops. Fourteen out of the 21 studies (67%) were general health assessments of the GM crop on rat health. Most of these studies (76%) were performed after the crop had been approved for human and/or animal consumption, with half of these being published at least nine years after approval. Our review also discovered an inconsistency in methodology and a lack of defined criteria for outcomes that would be considered toxicologically or pathologically significant. In addition, there was a lack of transparency in the methods and results, which made comparisons between the studies difficult. The evidence reviewed here demonstrates an incomplete picture regarding the toxicity (and safety) of GM products consumed by humans and animals. Therefore, each GM product should be assessed on merit, with appropriate studies performed to indicate the level of safety associated with them. Detailed guidelines should be developed which will allow for the generation of comparable and reproducible studies. This will establish a foundation for evidence-based guidelines, to better determine if GM food is safe for human and animal consumption.

Consumer acceptance of food crops developed by genome editing

“…These results sensationally emerged in mass media, with warnings that GM crops are unsafe for food consumption (Marshall 2007;Romeis, et al 2013). However, accumulating evidence from other animal feeding experiments suggest that current GM crops in the marketplace are predominantly safe (EFSA_GMO_Panel_Working_Group_on_Animal_Feeding_Trials 2008), although some criticisms about scientific justification and methodology consistency of animal toxicity studies performed so far were raised (Bartholomaeus, et al 2013;Zdziarski, et al 2014). In contrast, it should also be noted that some food products which are not genetically modified may affect human health.…”

Histopathological Investigation of the Stomach of Rats Fed a 60% Genetically Modified Corn Diet

“…However, histopathological or immunotoxicological studies on the effects of the proteins on animal physiology are scarce [30], particularly of the Cry proteins produced by GM crops [13], which are encoded by cry genes that have been modified, enhanced or synthetically produced [2]. The species-specific mode of action of Cry proteins are believed to be based on three things: 1) the insects' mid-gut proteases which cleave the Cry proteins, consequently activating the proteins by exposing their binding site [28]; 2) the activated proteins binding to the insects' specific cadherin receptor [69]; and 3) the Cry proteins binding to the insects' specific cell membrane receptor(s) [70] [71].…”

“…We recently published a review of histopathological studies investigating the digestive tract of rats fed a GM diet for 90 days or longer [13].…”

“…Thus far, few comprehensive investigations of the effect of GM crops on animal or human health have been published [11] [12] [13]. Furthermore, many of these studies measured animal production outcomes in farmed animals that are not physiologically comparable to humans and the measured variables were limited to those such as body weight, meat yield or milk production [14] [15] [16] [17].…”

“…A consideration of the digestive tract was deemed important since it is the first site of contact for any ingested compound, and hence the first site of possible toxicological or pathological changes that may arise due to a GM diet. The search was limited to long-term rat feeding studies of no less than 90 days duration and crops possessing one or more of three specific traits which are commonly found in commercialised GM crops: herbicide tolerance via an EPSPS gene, and insect resis- 765 Food and Nutrition Sciences tance via cry1Ab or cry3Bb1 genes [13]. Our study revealed that only 19% of the GM crops, known to possess at least one of the traits of interest, had been investigated via long-term feeding trials.…”