Will GMO wheat silence human genes?

A reader at the GMO Answers website recently posed this question:
QUESTION  “I recently looked at an article that states the new genetically modified wheat can silence wheat genes and can match human genes. This is a little concerning to me, seeing as I buy whole wheat bread and other products for my family to begin with. I have attached a link to the article stating this. Can you help clarify? http://www.undergroundhealth.com/genetically-modified-wheat-silences-dna-sequences-in-the-body-can-cause-fatalities-in-children/ (Natural Health News and Holistic Healing website)
Question Submitted by:  draechap2089 from West Memphis, AR
Yours truly (also humbly known at my personal blog as GMO Pundit ) had the opportunity to give an answer to draechap2089.
It was, in brief: Fortunately, recent research has proved this worrying claim to be false.
Even before these recent findings, there was a huge amount of scientific evidence showing that RNA eaten in food in the diet is very unlikely to ever reach a human gene and bring about gene silencing in the human body (summarised here by the Australian food safety regulator FSANZ ).

The Important Take Home Message is: Whole grain foods and food fiber are good for your health.

And the full answer  I gave explaining this message was the following:
 The Natural Health News and Holistic Healing website article in the link provided by this question about GM wheat raises really important and timely topics in human nutrition. It asks a good question about a genetically engineered wheat variety that has been developed by scientists at an Australian government crop-science institute called CSIRO.
These scientists used precise modern genetic methods to increase the fiber content of wheat. Food fiber is vital for good health, and adequate intake of food fiber may prevent colon cancer.
(See more discussion in Chapter 12, Diet and Cancer,  in David L. Katz 2008. Nutrition in Clinical Practice 2nd Edition). Unfortunately modern diets are often low in fiber content.
CSIRO’s new wheat is bred to contain high levels of a common form of food fiber called “invisible fiber”. Invisible fiber, also known as “resistant starch”, is a slowly digested natural variety of food starch that is present in many different plant foods. Slow digestion properties of this nutrient enable it to resist complete digestion while it is passing through the early stages of the digestive canal.
This means that some undigested resistant starch will always be able to reach the large bowel. In the large bowel it acts as an excellent source of nutritional energy for the gut surface tissue lining the lower bowel. It is this capacity to provide necessary energy for living human cells lining the bowel that makes invisible fiber a crucial nutrient for prolonging good health.
There is intense scientific and medical interest in a continually unfolding story of how diet, food-fiber, gut microbes and gut health are intricately interrelated, and undoubtedly there is much more for us all to learn. But we already know that readily available energy from food fiber is vital for gut health, and may well prevent colon cancer. It’s a message worth repeating many times that many modern diets do not contain enough food fiber for optimum gut health (e.g. see  Michael Conlon and colleagues 2012), and colon cancer is more frequent in communities that eat food that is generally low in fiber.

Whole grain cereals such as wheat and barley are at the centre of this unfolding story about healthier ways to eat (see a CSIRO BARLEYmax™ report here ).

Mutant wheat with high invisible fiber.

Much active research is being carried out at the CSIRO plant and nutrition research centres looking for ways to increase invisible fiber content in food grains. They have found that mutations to the wheat genes influencing starch formation yield wheat grain with an increased invisible fiber content.
Crop breeders have a choice between using less precise older (radiation based) methods for inducing mutation, or to use more precise and far less tedious modern methods. While the more precise modern methods attract the most public scrutiny and criticism, they are far less likely to introduce unintended extra genetic changes to the wheat than the imprecise radiation based traditional alternatives, which are not subject to intense public scrutiny or government regulation even though they are more risky.
The modern highly targeted approach used by CSIRO relies on a genetic engineering method that can be designed to precisely silence the wheat genes which influence starch content. The method uses plant genetic messenger molecules called RNA to achieve precisely targeted gene silencing (see here for more explanation ). RNA molecules are present in every human diet and are relatively abundant in foods.
The Natural Health News and Holistic Healing article had this to say about the CSIRO wheat:

“[Jack] Heinemann discovered that the molecules developed in this wheat, intended to silence wheat genes and can match human genes. With consumption, these molecules can enter the human body and potentially silence our genes, he explained. “The findings are absolutely assured. There is no doubt that these matches exist.”

Fortunately, recent research has proved this worrying claim to be false.
Even before these recent findings, there was a huge amount of scientific evidence showing that RNA eaten in food in the diet is very unlikely to ever reach a human gene and bring about gene silencing in the human body (summarised here by the Australian food safety regulator FSANZ ).
Simply put, the relevant wheat RNA molecules will be rapidly digested in the gut to harmless simple nutrients. Because of their size, they cannot easily enter the body, and in any case they will destroyed or eliminated from the bloodstream very rapidly, and they would require specialised mechanisms to be able to have any effect on human body functions. All of these reassuring characteristics about the harmlessness of RNA in our diet – a normal component of every human diet – are very well known to biologists and extensively documented.

Heinemann’s main speculative argument about the possible health risks of the CSIRO wheat rested almost exclusively on one highly controversial and disputed report published in 2012 by Chinese researchers, led by Chen-Yu Zhang, and appearing in the magazine Cell Research.
This report claimed to find that plant derived RNA molecules from rice could be enter inside an animal’s body from the gut and might be directly influencing animal metabolism. Given the previously mentioned large body of contrary evidence about RNA properties, many scientists strongly doubted these claims when they first appeared.
But in the last 6 months or so, these claims by Chen-Yu Zhang  have been heavily refuted in  follow-up investigations reported by several different, independent laboratories.
These include the labs of Kenneth Witwer at Johns Hopkins University, Jonathon Snow at Barnard College in New York; Brent Dickinson at miRagen Therapeutics, Colorado, and Jay Petrick and Ivan Ivashuta at the Monsanto Corporation (see for example here and here for discussion.)
These reports all confirm the conclusion that RNA molecules in foods (which have always been present in human diets) are unable to affect human genes inside the body because there are multiple hurdles that completely prevent their successful passage from the gut to sites of action within the body.  This inability of plant RNA cross the gut barrier has been repeatedly verified by recent scientific studies which conclusively demonstrate that plant RNAs in question are absent from the bloodstream.
Liver disturbances seemingly caused by rice dietary RNA were seen by Chen-Yu Zhang and colleagues  in the levels of a liver protein. (These, incidentally, were caused by a non GM rice, and did not indicate any harm had occurred.) The recent report by Brett Dickinson shows these are readily explainable as a nutritional imbalance simply caused by feeding experimental animals a diet with too much rice, and this does not need any further explanation.
Another safeguard against plant RNAs affecting human metabolism is an intentional lack of significant matches to any human genes. This safeguard can be deliberately designed into RNA molecules used to silence plant genes by checking the design of intended RNA sequences against human genome databases.
Such easily done database searching led to Jack Heinemann’s initial erroneous claims of unintended potentially adverse silencing of human genes by wheat RNA.
But Heinemann’s initial report used the wrong RNA sequence to evaluate hypothetical unintended silencing effects on humans and grossly inflated risk estimates. (See here for a discussion.)  In a revised 13 March 2013 version of his report he got different results, but it is still very feasible (and almost certain) that CSIRO would design a wheat silencing RNA to be much more narrowly focused on its target than the Heinemann 2013 second guess.

Conclusion

Positive health messages are the most important part of this story. Consumers should not worry about small amounts of RNA in their diet because it is digested rapidly into harmless nutrients.  There is no credible evidence that silencing RNA molecules from plants in the diet can have any effect on human metabolism. Everyone should  benefit from making sure they regularly include in their diet foods such as whole grains, barley, oats, beans, fruits and vegetables that provide food fiber.  (See e.g. David Katz, 2013 , Disease-Proof: ) And we should all look forward to new varieties of wheat being commercialised that are rich in health promoting invisible fiber. Whether or not they are GM or from irradiated non-GM wheat mutants is still an open question.
 Originally published as a Q and A @  GMO Answers
 
Also see:
GMO Wheat and shouting “fire” in a crowded theater
Update (thanks to Mary in comments) : see also an earlier post:
Why novel dsRNA molecules in GM food are of little to no concern