A meta-analysis is a formal way to combine many papers on related topics to come to some overall conclusions (see 5 key things to know about meta-analysis). There have been large GE crops literature reviews in the past, but none to date have actually compiled all of that data into a meta-analysis.
The researchers reviewed 6,006 studies in the peer-reviewed literature from 1996 to 2016, including papers on yield, grain quality, target organisms (pests), non-target organisms, and soil biomass decomposition. Amusingly but not surprisingly, most of the studies took place in the US corn belt: Iowa, Illinois, and Nebraska. The researchers excluded experiments that were not performed under field conditions, that did not use a genetically similar (near isogenic) comparator, that had GE and non-GE corn grown under different conditions, or that had small sample sizes or other statistical issues. That left only 76 publications in the meta-analysis.
One drawback to this meta-analysis is that it groups GE traits in corn together. Each type of GE trait has benefits and drawbacks and typically must be considered individually. That said, in public discourse, specific GE traits are rarely discussed and people simply say “GMOs”. In that context, this meta-analysis is helpful in answering concerns about the effects of “GMOs”. The researchers “noted that single event [herbicide tolerant] hybrids were missing”. In other words, studies included GE herbicide tolerance only when combined (stacked) with GE insect resistance traits. Effectively, this is a meta-analysis on corn with GE insect resistance traits, not on all currently available GE corn.
The results of the meta-analysis are striking. As you can see in Figure 3a from the paper, corn yield was increased overall in GE corn compared to non-GE corn. There were small differences in how much yield was increased depending on whether the varieties had 1, 2, 3, or 4 biotech traits (single stack, SS; double stacked, DS; triple stacked, TS; and quadruple stacked, QS), with quadruple stack having the highest yield.
There were also fewer damaged ears overall in GE corn compared to non-GE corn. This is important because damage to the corn leads to fungal infection, which leads to potentially deadly mycotoxins. There was no significant difference in ear damage between single trait varieties and genetically similar non-GE varieties, but there was a significant difference in yield, which is interesting because you’d expect these two measurements to be more correlated. It’s also interesting that quadruple stacks had much less damage than triple stacks, but only a little less than double stacks.
Figure 3b shows that overall GE corn has less mycotoxins, great news since mycotoxins can cause all sorts of ill effects in humans and animals who eat them. The rate of decomposition (residue mass loss) was higher in GE corn than in non-GE corn.
The major pest corn rootworm (Diabrotica) was reduced in GE corn, not a surprise since that is the target pest of many GE insect resistance traits. Beneficial parasitic wasps (Braconidae) were also decreased in GE corn, possibly due to greatly reduced numbers of corn rootworm hosts. The minor pest leafhoppers (Cicadellidae) were increased in GE corn, possibly because the use of insect resistance traits reduces the need for broad spectrum insecticides.
Many beneficial arthropods were not affected by the use of GE corn: pirate bug (Anthocoridae), spider (Araneae), ground beetle (Carabidae), lacewings (Chrysopidae), lady bug (Coccinellidae), damsel bug (Nabidae), sap beetle (Nitidulidae), rove beetle (Staphylinidae). Pest aphids (Aphididae) were also not affected by the use of GE corn. This was surprising. I expected that there would be higher prevalence of many beneficial and pest insects in GE corn compared to non-GE corn due to reduced treatments with broad spectrum insecticides.
Another not-very surprising finding was that there were no significant differences in grain quality: proteins, lipids (fats), or fiber. There was also no difference in the lignin in stalks or leaves. This confirms that corn is corn, whether it is GE or not. It would be nice to see meta-analysis on minor constituents of GE and non-GE corn, such as particular vitamins or limiting amino acids. The researchers for this study add biodiversity and soil biogeochemical cycles to the wish list of items they’d like to see studied. Even with the limitations of what is available in the literature, this meta-analysis shows once again that crops produced with biotechnology are some of if not the most studied foods that we eat.