Here we go again. A pseudoscience pushing website (which occasionally tosses in stories about real science) is trumpeting a primary research study (published 6 months ago) that may, or may not, indicate that plant DNA may survive intact in the digestive tract and show up in the bloodstream. You just know what they’re going to say next.
This will now be all about genetically modified foods.
In case you’ve ignored this area of pseudoscience, genetically modified crops are foods derived from genetically modified organisms (GMOs); of course, all types of agricultural breeding induces genetic modification, but in general, GMO usually implies actual manipulation of the genes. Based on some of the worst science available, anti-GMO cultists have condemned GMO foods as being dangerous. Of course, there is actually no science supporting the anti-GMO claim, and the vast scientific consensus says that GMO foods are safe to humans, animals and the environment.
A paper published in the online journal, PLoS One, seems to indicate that possible DNA fragments pass from the digestive tract into the blood. The authors, Spisak et al., concluded:
…based on the analysis of over 1000 human samples from four independent studies, we report evidence that meal-derived DNA fragments which are large enough to carry complete genes can avoid degradation and through an unknown mechanism enter the human circulation system.
Based on our knowledge of the digestive process, fats, DNA, carbohydrates, and proteins are broken down into their simplest components, and specialized transport systems move these simple components across the barrier between the digestive tract and blood. They have evolved to not transport full size molecules, partially because the blood is incapable of carrying large foreign molecules (and could induce an immune response). Moreover, small constituent molecules, like amino acids instead of the whole protein, or glucose instead of a long-chain carbohydrate, are more easily transported to locations in the body to be then used as fuel or building blocks for new proteins and DNA. We just have not seen a mechanism in the digestive tract that can move large molecules, like gene-length DNA fragments, into the bloodstream.
In fact, the authors admit that the mechanism is unknown, though it’s curious that years of study of the molecular transport of nutrients has never uncovered this until 2013. Based on this limited evidence, here’s what the anti-GMO crowd says about it:
What biotechnology and biotech corporations like Monsanto have done, is they have allowed for the transfer of genes from one to the other without any regard for the biological limitations, or constraints. The problem with this is that it is based on very bad science. The conditions and biological ‘rules’ that apply to vertical gene transfer, at least those that we are aware of, do not necessarily apply to horizontal gene transfer. Biotech science today is based on the assumption that the principles governing the inheritance of genes are the same when we move genes horizontally as they are when they are moved vertically. It just goes to show that GMO’s should be subjected to much more experimentation and rigorous research before we continue to consume them.
Oh no. Franken-foods might cause franken-humans. And because…Monsanto.
But since this is a skeptical website, let’s look at this research and the conclusions of the anti-GMO lunatics more carefully:
- This study is a primary publication that has not been confirmed by subsequent research. On the list of scientific evidence, the quality of primary research is good, but not great, and certainly not enough to establish a firm scientific consensus.
- The study was published in a moderately low impact factor (3.730) open access, online journal, PLoS One, which has the publication philosophy of “publish first, judge later.” Well, we’re judging now.
- The study examine minuscule levels of DNA in blood, nanogram levels. We definitely are able to detect nanogram levels of DNA, but at that low level, substantial risk of contamination is so high, that if one were to see these results, the initial hypothesis would probably be “this blood sample was contaminated,” rather than the infinitely more complex and undiscovered mechanism to move these huge molecules into the blood. Yes, Occam’s Razor does apply, the simplest explanation might be the best.
- In fact, RW Lusk of the University of Michigan, spent six months reviewing the data and methods of Spisak et al. and concluded that they must consider contamination as the source of plant DNA, not some mysterious digestive mechanism. Lusk stated that contamination can account for these results, because DNA measurement is so sensitive, that even washed laboratory equipment harbors DNA fragments.
- In a review of the papers by Spisak et al. and Lusk, it was concluded that “Poor commentary and cherry-picking data helps no one. Spisak’s study tells us about a significant biological finding that needs to be carefully analysed. The cautionary tale is that one must not extrapolate wildly from good science to create horrific scenarios that are not based on any scientific observations whatsoever.” In other words, even if Spisak’s work is not set aside by potential contamination, it doesn’t say anything about anything dangerous about modified DNA.
- But let’s assume that there’s some unknown, mysterious mechanism that allows DNA to be transmitted into the blood (while excluding long chain carbohydrates, whole proteins, and other large molecules). The numbers are so small, just a handful complete genes, that the probability that those DNA molecules will have any effect on the body is near 0.
- Genes don’t easily jump from one species to another. If gene transfer were so simple, the medical usefulness of gene therapy would be extremely high, instead of being incredibly difficult. We’re trying to transfer genes to cure diseases, and we’re finding it almost impossible. If consuming a few kernels of corn, introduced some gene into the bloodstream that somehow gets incorporated into the human genome, well that would be a miracle. But reality is, even if the article is accurate, and there’s doubt to that, it has little clinical meaning.
- But the most important thing is that if there is some heretofore mysterious mechanism to transfer DNA from the digestive tract to the human genome, it should be noted that nearly everything we consume contains DNA. The probability that any number of DNA fragments from hamburger, salads, cereal, eggs, or the billion other foods will eat getting into the bloodstream is higher, substantially higher, than a modified DNA fragment. But we don’t turn into corn. Or lettuce. Or a cow. Or a chicken. It just doesn’t happen.
I don’t know if the study in PLoS One is going to stand given the high probability of contamination, which has been demonstrated by another researcher. But even if it is confirmed by other research or becomes the initial observation that leads to a new mechanism of transport of nutrients, it provides NO evidence whatsoever that GMO’s suddenly become dangerous because those genes will be incorporated into our human genome. You may as well become worried that we’ll turn into a chicken after eating an egg.
Note: This updated article was originally published on 25 February 2014.
- Lusk RW. Diverse and widespread contamination evident in the unmapped depths of high throughput sequencing data. arXiv:1401.7975 [q-bio.GN]. 2014 January.
- Spisák S, Solymosi N, Ittzés P, Bodor A, Kondor D, Vattay G, Barták BK, Sipos F, Galamb O, Tulassay Z, Szállási Z, Rasmussen S, Sicheritz-Ponten T, Brunak S, Molnár B, Csabai I. Complete genes may pass from food to human blood. PLoS One. 2013 Jul 30;8(7):e69805. doi: 10.1371/journal.pone.0069805. Print 2013. PubMed PMID: 23936105; PubMed Central PMCID: PMC3728338.