The Problem with [GM] Nutritionally Enhanced Plants
Nutritionally enhanced (by GM technology) tomatoes amongst others have been in the news recently. This article from The Organic Center in the US highlights some of the problems and shortcomings of this approach.
Dr. David Schubert is a highly regarded molecular biologist focusing on neurological development. He is based at the Salk Institute for Biological Studies in California and has just published a provocative "Perspective" piece on applications of genetic engineering to enhance the nutrient density of plants in the Journal of Medicinal Food (Vol. 11, No. 4).
Schubert explains why it has been difficult for the biotechnology industry to develop protein-based pharmaceuticals in plants. Problems arise with protein-based plant compounds because of their reactivity, especially their proclivity toward glycosylation. As sugars attach and are cleaved from protein compounds produced in plants, both their metabolism and bioavailability changes, making it very difficult to control doses, predict interactions with drugs or other biologically active secondary plant metabolites, or achieve consistently a desired impact on human health.
On the other hand, Schubert points out that nutritionally-enhanced plants (NEPs) are less subject to such problems and are likely to be viewed by the Food and Drug Administration (FDA) as "generally recognized as safe" (GRAS).
But NEPs face their own unique problems, according to Schubert. For example, Golden rice is genetically engineered to produce higher levels of B-carotene (precursor of Vitamin A). Many enzymes are known to alter the form and metabolism of carotenoids like B-carotene, producing the common retinoids Ë† retinol (Vitamin A), retinal, and retinoic acid (RA). Retinal is oxidized to retinoic acid, which is far more active and toxic than Vitamin A.
While low doses of RA play an essential role in neurological development, they can bioaccumulate in fat tissues and plasma, and research has shown that multiple, low doses are more toxic than a single, high dose. Given the importance of RA, its toxicity, and the potential to alter RA levels and forms as a result of genetic engineering, Schubert warns that Ë†
"...excess RA, or RA derivatives are exceedingly dangerous, particularly to infants and during pregnancy...extensive safety testing should be required before the introduction of golden rice as food."
(The most common PMP (Plant-made Pharmaceuticals) crops that have been grown in U.S. field trials are corn, tobacco, and rice. Other crops being investigated include alfalfa, potato, safflower, soybean, sugarcane, and tomato.)
In the case of plants genetically-engineered to produce higher levels of fatty acids like omega 3s or conjugated linoleic acid, Schubert points out that GE-plant transformations can lead to the formation of slightly altered forms of fatty acids, which in turn can increase the risk of Alzheimer's disease.
In other cases, plants expressing markedly elevated levels of certain nutrients, or forms of nutrients, might push periodic intake into the possibly toxic zone. (Recall from past stories in "The Scoop" that most beneficial antioxidants become pro-oxidants at excessively high doses).
While minimally necessary intake levels have been carefully studied for many nutrients, possibly damaging high levels of consumption have received much less attention.
GE Soybeans with Elevated Omega 3 Fatty Acids in the Pipeline
Monsanto has genetically engineered soybeans to increase the level of omega 3 fatty acid. A small, preliminary study carried out at the University of South Dakota found that consumption of the GE-soybeans increased blood omega 3 levels by 4 to 5 percent, enough to reduce the risk of heart attacks by as much as 50%.
Monsanto hopes the new soybeans will be approved for commercial planting by 2011, leading to consumer products in the supermarket by 2012.
Source: Graham Tibbetts, "GM Soya Bean Could Prevent Heart Attacks and Save Fish Stocks," The Telegraph, November 3, 2008
Nutritionally Enhanced GE-Foods Still "Years Away"
A story in the November 3rd Washington Post by Marc Kaufman surveys the prospects for nutritionally enhanced, GE-foods and concludes that such foods are still "years away."
The piece begins with an overview of the generally optimistic, but unfulfilled hopes for nutritionally enhanced GE-foods. Kaufman then describes a purple tomato that has been engineered to express high levels of anthocyanins, the antioxidant compounds that give many fruits and vegetables their deep, rich colors. Genes from snapdragon plants were used to create the purple tomatoes.
Cathie Martin, one of the scientists working on the purple tomato, acknowledges that there are several conventional foods with elevated levels of anthocyanins, in particular dark raspberries and blackberries. The goal, however, is to create a common food like tomatoes with elevated anthocyanins levels so that more people might someday increase their daily intakes of antioxidants. Martin argues that a person could get enough antioxidants for a day by eating one purple tomato, compared to five servings of conventional fruits and vegetables.
Other teams are working to boost the level of resveratrol in grapes and wine, an antioxidant known to help protect heart health and trigger a sense of fullness (often referred to as satiety).
Typically, two or more genes, and/or transcription factors, must be engineered into a food crop to enhance nutritional quality. These more complex genetic modifications can lead to a diversity of unanticipated outcomes, and will require careful study before approval by regulators.
Margaret Mellon, a molecular biologist working for the Union of Concerned Scientists, expresses scepticism that the biotechnology industry will be able to deliver on its promise to create nutritionally-enhanced foods. She states that Ë† "Clearly, genetically engineered fruits and vegetables for nutritional benefits has proven far more difficult than the industry expected."
Organic Center Editor's Note:
Consumers hoping to boost their antioxidant intakes do not have to wait for purple tomatoes, nor does the food industry need GE-technology to dramatically boost antioxidant nutrient density in common, conventional fruits and vegetables.
Our research shows that a well-managed, long-term organic farm will produce fruits and vegetables that are, on average, about 30% higher in total antioxidants. By choosing from the dozens of fruits and vegetables that are naturally high in antioxidants, and then buying organic, consumers can easily meet and exceed their daily need for around 3,500 ORAC units, a goal for daily antioxidant intakes put forth by scientists at Tufts University.
See our antioxidant "State of Science Review," and especially Table 2, where 37 foods are listed that deliver 1,000 or more ORAC units per serving. Wild blackberries, a super-rich source of anthocyanins, contain 13,353 ORAC units per 1 cup serving Ë† more than three-times a person's daily needs.
Check out the table to learn which ten foods deliver 100 or more ORAC units per calorie consumed. Just a 35 calorie portion of these foods delivers a person's daily dose of antioxidants.
One other important point is relevant to the notion of a single purple tomato meeting one's daily needs for antioxidants. Scientists agree that everyone should consume several antioxidant rich foods every day.
For optimal health benefits, choose fruits and vegetables with multiple colors and flavors. Spread out the consumption of these nutrient-rich foods throughout the day. A greater portion of the nutrients in fruits and vegetables are likely to be taken up by your body when consumed in this way.
A diverse pattern of consumption of nutrient-dense foods throughout the day, encompassing multiple colors, will help assure stable levels of antioxidants in your bloodstream, where they are needed to protect against cell damage triggered by reactive oxygen species, otherwise known as free radicals.
Date: Wednesday 12th November 2008
Source: The Organic Center
NOTE: The full Schubert paper is available here: http://www.theecologist.org/pdf/NEPS.pdf