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We are genetically modifying crops to change the way they look, to produce more out of less, or to make them resistant to certain diseases; they are subsequently being consumed by humans and animals.

What, if any, are the side effects or harmful effects on the human body caused by consuming these products? Does this include any long term health effects?

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    I'm afraid this question is too broad. – Shlublu Apr 9 '15 at 9:32
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    I disagree; I think it's a good question. "Are there any long-term health effects" is valid. – Nate Barbettini Apr 9 '15 at 12:20
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    @NateBarbettini The answer shown me that this question can actually be answered. I retracted my close vote. – Shlublu Apr 9 '15 at 12:22
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GM food topic is controversial and it's subject of protests, vandalism, referenda, legislation, court action and scientific disputes and this involve consumers, biotechnology companies, governmental regulators, non-governmental organizations and scientists.

The main concerns about GM (genetic modified) food and crops is whether they have any negative effects on our health and the environment. And before implementation of these new GM strategies, we should take a full risk assessment which is necessary to understand the possible impacts.

Transgenesis of food organisms is likely to grow further and used in the world food supply.

Genetic engineering and breeding has aim of building plants that are superior ("superweeds" and "superbugs") which holds great promise.

GM crops (such as corn, soybean, rapeseed and cotton) already been produced a range of GM characters such as:

  • resistance to certain viral pathogens (cucumber mosaic virus), insect, pests, diseases (citrus greening disease) or environmental conditions,
  • reduction of spoilage,
  • resistance to chemical treatments (e.g. herbicide),
  • enhancing yields or improved nutritional value,
  • modification of enzymes involved in bioprocessing2006, 2007,
  • altering oil content,
  • tomato - delayed fruit ripening,
  • alfalfa - aimed at the reduction of lignin contentwiki,
  • and many more

Health concerns

However some health groups claim that there is potential long-term impact on human health have not been adequately assessed2004,2007, however the broad scientific consensus is that food on the market derived from GM crops poses no greater risk than conventional food2010, 2011, 2012.

In general those who create genetically engineered seeds argue the seeds are safe and critics say that FDA has relied on studies the industry paid for in comparison with overseas studies which show increasing signs of concern (e.g. increasing the size of organs in mice).

The main concerns raised by BMA (PDF) in 2004 are:

  • Allergens.

    • Possible effects of GM foods on allergic responses.

      It remains possible that any new food products could elicit new allergies.

      There is evidence that the food matrix can affect the release of other nutrients during digestion and it seems likely that it can also influence the release and digestion of allergens in the digestive tract.

      With regard to sensitisation it is still not known whether other components in the food matrix can have an adjuvant effect on the development of IgE responses in susceptible individuals.

      The concerns are that they may contain allergenic substances due to introduction of new genes into crops2003.

  • Nutritional status2003.

    It is possible that GM technology could lead to unpredicted harmful changes in the nutritional status of foodsMRC 2000.

    GM foods could conceivably have different effects on those of poor nutritional status and/or those belonging to ‘vulnerable groups’ (notably the foetus, infants, children, pregnant and lactating women, the elderly and those with chronic disease) when compared with healthy individuals.

  • Genetic transfer.

    • The fate of GM plant DNA in the digestive system.

      While gene transfer has been observed in the gastrointestinal tract of some mammals 1991, 1993 and birds 1999 there is still great uncertainty as to the extent and the consequences of this transfer 2002.

    • Potential effects on human health resulting from the use of viral DNA in plants.

      Plant viral DNA sequences are commonly used in the construction of the genes inserted into GM plants.

      The concern is that genetic engineering often involves the use of antibiotic-resistance genes as "selectable markers" and this could lead to production of antibiotic-resistant bacterial strains that are resistant to available antibiotics. This would create a serious public health problem.2003

  • Environmental impact.

    Recent UK Farm Scale Evaluations of GM herbicide-tolerant crops (GMHT)2003 indicate that if GMHT beet and spring oilseed rape were introduced and managed as they were in the trial, a significant reduction would be expected in weed biomass and weed seed return. This would result in fewer nectar resources for pollinators and fewer weed seed resources for granivorous birds.

    Canadian farmers found that their fields filled with stray GM crop plants known as ‘volunteers’. These were resistant, not only to the substance against which the main crop was engineered, but to the other two herbicides used as well.2002

    The potential impact of GM crops on the environment and biological diversity is the issue that has given rise to most concern and it remains in doubt2003.

  • Experimental design.

    Research into the possible health effects of GM foods in this country has been limited to date by the lack of firm hypotheses regarding such effects, difficulties of defining individual consumption, and the generally low levels of consumption of GM foods.

Some other groups such as Greenpeace and WWF have concerns that risks of GM food have not been adequately identified and managed.

One cellular biologist, David Williams, says that anyone in this field knows that genome is not a static environment and can be transformed by several different means, and it can happen generations later which can result in potentially toxic plants slipping through testingD. Williams.

Some other studies indicated that there may be specific health risks associated with consumption of GM foods, such as:


Other concerns

People questioning this new technology and activists around the world demonstrate to express their concerns while food industries trying to push this technology forward.

There are common claims from opponents that consumption of GM can cause cancer or birth defects, however there currently is no evidence to support this claim.

Currently labeling of GMO products in the marketplace is required over 60 countries2014, the US does not require this.


Conclusion

Based on above, many unanswered questions remain, especially with potential long-term impact of GM foods on animal and human health and the environment and it currently. The GM foods are very complex and currently there is a lack of evidence-based research with regard to medium/long-effects on health and it remains as a matter of great public concern. Further research is required on how best to carry the experiments (modern profiling techniques and define the 'normal' compositions of conventional plants), risk assessments and surveillance studies with respect to GM crops and foods.

The Royal Society in their 2002 report saying there is at present no evidence that GM foods cause allergic reactions, use of specific viral DNA sequences in GM plants are negligible and conclude that consumption poses no significant risk to human health, and that ingestion of GM DNA has no effect.

Study from 2003 by J Toxicol Environ Health summarise it:

The review of available literature indicates that the genetically modified crops available in the market that are intended for human consumption are generally safe; their consumption is not associated with serious health problems. However, because of potential for exposure of a large segment of human population to genetically modified foods, more research is needed to ensure that the genetically modified foods are safe for human consumption.

Currently the broad scientific consensus states that food on the market derived from GM crops poses no greater risk to human health than conventional food2010, 2011, 2012.


Further readings:

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    Good answer. Although I disagree that there is a lack of solid research on long-term effects - I'll see if I can dig some sources up. – Nate Barbettini Apr 9 '15 at 12:12
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    @NateBarbettini Probably quite hard to find long term, due to the time they have been around. – Tim Apr 9 '15 at 12:54
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    Unfortunately, it is of "great public concern" because of fearmongering. The vocal minority is, well, vocal. – JohnP Apr 9 '15 at 14:59
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    @kenorb - I haven't done a lot of looking on GMO studies, as there are few independent studies. Lots that are sponsored by Monsanto or similar touting the safety, and some paid for by GMO opponents that find (Surprise) possible harmful effects. It's been championed lately because people want to sell stuff. Make people afraid of it, tell them who's to blame, then sell your solution book/blog/lecture series. – JohnP Apr 9 '15 at 17:22
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    @kenorb We understand what the genetic modifications in GMOs do, there is no reason why those very specific mutations should be more harmful than the random ones done by selective breeding. – Mad Scientist Apr 9 '15 at 21:49
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The WHO considers the genetically modified food currently on the market to be safe

8. Are GM foods safe?

Different GM organisms include different genes inserted in different ways. This means that individual GM foods and their safety should be assessed on a case-by-case basis and that it is not possible to make general statements on the safety of all GM foods.

GM foods currently available on the international market have passed safety assessments and are not likely to present risks for human health. In addition, no effects on human health have been shown as a result of the consumption of such foods by the general population in the countries where they have been approved. Continuous application of safety assessments based on the Codex Alimentarius principles and, where appropriate, adequate post market monitoring, should form the basis for ensuring the safety of GM foods.

The FDA also considers them safe

3. Are foods from genetically engineered plants safe?

Foods from genetically engineered plants must meet the same requirements, including safety requirements, as foods from traditionally bred plants. FDA has a consultation process that encourages developers of genetically engineered plants to consult with FDA before marketing their products. This process helps developers determine the necessary steps to ensure their food products are safe and lawful. The goal of the consultation process is to ensure that any safety or other regulatory issues related to a food product are resolved before commercial distribution. Foods from genetically engineered plants intended to be grown in the United States that have been evaluated by FDA through the consultation process have not gone on the market until the FDA’s questions about the safety of such products have been resolved.

8. Are foods from genetically engineered plants more likely to (1) cause an allergic reaction or (2) be toxic?

The foods we have evaluated through the consultation process have not been more likely to cause an allergic or toxic reaction than foods from traditionally bred plants. When new genetic traits are introduced into plants, the developer evaluates whether any new material could be (1) allergenic or (2) toxic if consumed in foods made from the genetically engineered plants or from ingredients derived from these plants.

10. Are there long-term health effects of foods from genetically engineered plants?

When evaluating the safety of food from genetically engineered plants, scientists with experience in assessing the long-term safety of food and food ingredients consider several factors, such as information about the long-term safety of the food from traditionally bred crops in combination with information on the food safety of the newly introduced traits. Foods from genetically engineered plants that have been evaluated by FDA through the consultation process have not gone on the market until the FDA’s questions about the safety of such products have been resolved.

The AAAS also declared that eating Genetically modified food is safe:

The World Health Organization, the American Medical Association, the U.S. National Academy of Sciences, the British Royal Society, and every other respected organization that has examined the evidence has come to the same conclusion: consuming foods containing ingredients derived from GM crops is no riskier than consuming the same foods containing ingredients from crop plants modified by conventional plant improvement techniques.

There is a broad scientific consensus that the genetically modified crops on the market are safe. There is also quite rigorous testing of any new GM crop before they are approved.

There are real concerns like allergies, as genetically modified organisms typically add a protein that wasn't present before in those organisms. Any protein can potentially be allergenic, because of this the allergenicity is tested before the modified crop is approved.

There are a few studies that showed negative effects of GMOs on rats, but most of them were from a single research group lead by Gilles-Éric Séralini and have been widely criticized (summary of the Séralini results and the criticism on Wikipedia, Blog post on Science Based Medicine). The 2012 study from Séralini was also retracted by the publisher and they stated that no conclusions could be reached from the experiments, mostly because the sample size was too small.

There is a vast consensus among scientists and regulatory agencies that genetically modified food is safe.

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    You mentioned several organizations that say GMOs are safe, but what about counter-examples? Why is growing GM crops not allowed in most countries in the European Union? – THelper Aug 7 '16 at 20:13

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