Is Genetically Modified food safe to consume?

Question

What's the truth surrounding the popular idea that genetically modified food is dangerous to consume?

There's entire websites and institutions dedicated to popularizing the alleged dangers of eating genetically modified food, such as GMO Awareness, Food Revolution Network and the Institute for Responsible Technology. There's countless articles and even a TED Talk video.

On the flipside, there are also lots of reputable articles saying that all evidences points to GM food being safe: This recent one in Forbes, Alleged Danger of GMOs Not Looking Very Real or this one from Slate, GMO Opponents Are the Climate Skeptics of the Left. Sites such as Sense about Science point out that we've been altering plant's genetic structures for thousands of years, and genetic modification is just a new way of doing this old process.

A different argument I read in the Huffington Post states that Pesticide Use Proliferating With GMO Crops is the real source of danger. So even if GMO food itself is fine to eat, what about the secondary dangers from increased/stronger pesticide use that comes as a direct result of GMO crops?

So much conflicting information, but what does the scientific evidence say?

Answer 1

Yes, genetically modified organisms (GMOs) are safe to consume.

The American Association for the Advancement of Science, American Medical Association, World Health Organization, Food and Drug Administration, EU researchers all agree that GMOs are safe to eat.

From the American Medical Association:

Bioengineered foods have been consumed for close to 20 years, and during that time, no overt consequences on human health have been reported and/or substantiated in the peer-reviewed literature

and from the World Health Organization:

GM foods currently available on the international market have passed risk 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.

Though some sources admit the possibility of risk from unexpected allergic reactions or gene transfer, they note that required testing for GMOs has meant that no GMOs on the market pose a risk to consumers.

You may see people reference one study by a scientist named Séralini, which found that GMOs cause cancer in rats, but that study has been thoroughly debunked. Séralini had an insufficient sample size, used a strain of rats likely to develop cancer anyway, and released his paper to the press before he released it to peer review. His results do not match the scientific consensus.

In summary: the scientific consensus is that GMOs are safe to consume, and not a single health problem has ever been attributed to genetically modified foods in the decades we've been eating them.

UPDATE: The aforementioned debunked Séralini study has been retracted.

Answer 2

The question needs to be answered on a case-by-case basis. Certainly, not all GMO food is toxic, and the process of GMO does not inherently lead to toxicity. On the other hand, there is no guarantee that novel gene combinations can never lead to increased toxicity for individual organisms.

Below I have collected some sources, either neutral ones, or focussing on the risks. I did not include information from sources with a commercial interest in GMO, such as Monsanto, as I am of the opinion that information from corporate sources deserves to be distrusted.

A recent review study

According to Domingo et. al. (2011), who did an overview of studies into this question, the number of references concerning human and animal toxicological/health risks studies on GM foods/plants was very limited.

Domingo, J. L. & Giné Bordonaba, J. Environ. Int. 37, 734–742 (2011). Weblink.

The article is behind a paywall, but the abstract summarises:

An equilibrium in the number research groups suggesting, on the basis of their studies, that a number of varieties of GM products (mainly maize and soybeans) are as safe and nutritious as the respective conventional non-GM plant, and those raising still serious concerns, was currently observed. Nevertheless, it should be noted that most of these studies have been conducted by biotechnology companies responsible of commercializing these GM plants

This review was from 2011.

United Nations Environmental Programme assessment

The International Assessment of Agricultural Knowledge, Science and Technology for Development, an international effort co-sponsored by FAO, GEF, UNDP, UNEP, UNESCO, the World Bank and WHO, issued a lengthy report assessing what the title says. This includes (but is not limited to) issues related to GMO. Several reports, as well as summaries, are linked from the United Stations Environmental Programme IAASTD page. Specifically on the safe to consume for humans issue, they write on page 200 in the global report (emphasis theirs):

The safety of GMO foods and feed is controversial due to limited available data, particularly for long-term nutritional consumption and chronic exposure.

Food safety is a major issue in the GMO debate. Potential concerns include alteration in nutritional quality of foods, toxicity, antibiotic resistance, and allergenicity from consuming GM foods. The concepts and techniques used for evaluating food and feed safety have been outlined (WHO, 2005b), but the approval process of GM crops is considered inadequate (Spök et al., 2004). Under current practice, data are provided by the companies owning the genetic materials, making independent verification difficult or impossible. Recently, the data for regulatory approval of a new Bt-maize variety (Mon863) was challenged. Significant effects have been found on a number of measured parameters and a call has been made for more research to establish their safety (Seralini et al., 2007). For example, the systemic broad spectrum herbicide glyphosate is increasingly used on herbicide resistant soybean, resulting in the presence of measurable concentrations of residues and metabolites of glyphosate in soybean products (Arregui et al., 2004). In 1996, EPA reestablished pesticide thresholds for glyphosate in various soybean products setting standards for the presence of such residues in herbicide resistant crop plants (EPA, 1996ab). However, no data on long-term consumption of low doses of glyphosate metabolites have been collected.

For the sake of completion, they define GMO (Genetically Modified Organism) as An organism in which the genetic material has been altered anthropogenically by means of gene or cell technologies..

Union of Concerned Scientists point of view

The Union of Concerned Scientists is a an advocacy organisation, and not necessarily objective. However, I do think their assessments are evidence-based, so I think their point of view is worth quoting:

So far, scientists know of no inherent, generic harms associated with GE organisms. For example, it is not true that all GE foods are toxic or that all engineered organisms are likely to proliferate if released into the environment.

But specific enginereed organisms may have specific harmful effects by virtue of the novel gene combinations they possess. This means that the risks of genetically engineered organisms may vary widely, and therefore must be assessed on a case-by-case basis.

Specifically about toxins, they write:

Production of New Toxins

Many organisms have the ability to produce toxic substances, which help to defend them from predators. Some plants contain inactive genetic pathways leading to toxic substances, and new genetic material introduced through GE could reactivate these pathways or otherwise increase the plant's production of toxic substances. This might happen, for instance, if on/off signals associated with an introduced gene are located on the genome in places where they could turn on the previously inactive genes for producing the toxins.

Other studies

More recently, Séralini et. al (2012) conclude that a particular kind of genetically modified food is harmful to rats, but only on timescales similar to the rats lifetime, which would suggest that effects in humans may only become visible on a timescale of decades. The work by Séralini is highly controversial. He has been accused of fraud and his articles have been described as debunked; whether this is true or a sign of the debate itself being toxic, I don't know. Wikipedia has a whole article Séralini affair, which links further to himself and his articles. They're too controversial to base any conclusions upon, really.

An advocacy group called Earth Open Source has published a report GMO Myths and Truths, where GMO is understood as genetically engineered crops. This document specifically collects material critical of GMO, and is therefore not objective by itself, but it does build upon peer-reviewed publications and the authors have PhDs in relevant fields (molecular genetics and biochemistry). They list a number of studies linking how GMO's can be toxic, similarly to the note by the Union of Concerned Scientists.

Concluding note

"Safe to consume" or "harmful to humans" can relate to direct or indirect effects. Not all GMO food is automatically unsafe, but there exist secondary effects. For example, some GMO adoption leads to increased pesticide use, and there exist ecological risks which can indirectly affect human health. For further reading, these issues are addressed by the Union of Concerned Scientists, the UNEP, and the Earth Open Source report.

The scientific debate continues.