The Carman study confirms some previous long-term studies which found indications of toxicity of some commonly used GM crops fed to animals and the non-academic perception by many farmers and veterinarians that these crops were intoxicating their animals.
Judy Carman et al., A long-term toxicology study on pigs fed a combined genetically modified (GM) soy and GM maize diet. Organic Systems 2013. Freely available → LINK (alternative link). [ISSN 1177-4258]
The first link was not available at the time of writing this because of exceeded bandwidth, a clear sign of the massive interest that this study has triggered. In fact the Internet is already full of Biotech-financed defamatory articles, which range in content from such ingenuous remarks as "when pigs fly!" to "hogwash!". At least it is quite funny to watch how mercenary pens feel the need to be creative to fill in the void caused by their otherwise depressive job of systematic lying.
But there are also more seriously concerned articles all around, in fact, once we overcome the first page or two of the search engine's hits, most are concerns and worries about the GMO caused foodpocalypse.
Focusing on the substance of the study, Carman and colleagues first review the scarce literature on the effects of GM-foods on animals, finding that often those studies are too short-term, not considering mid and long term toxicity. Also many of these Biotech-friendly studies, typically financed by the very same GMO companies that produce the crops, used non-mammals (birds, fish), food types not eaten by humans like fermented green fodder (silage) or only measured animal productivity and not health as such.
A few studies however are more throughout. For example Séralini 2011, reviewing past 90-days feeding studies, finding evidence of liver and kidney damage caused by GM-crops, concluding that 90 days was not enough to evaluate the toxicity of these novel bioengineered foodstuff.
Poulter 2012, a two-year length study on NK603 herbicide-tolerant corn, found evidence of higher death rates, more tumors and liver and kidney pathologies being caused by the crop.
Carman et al. therefore aimed to do a long term study of 22.7 weeks in animals whose physiology is similar to humans: pigs. This is almost unprecedented in GMO studies.
They used 168 pigs randomly divided in two groups of 84 each. One was fed GM-modified corn and soy, as is usually done in US farms (specifically the very common Ht soy, and Ht and Bt corn) within a mixed diet, as is usually done in farms. The control group was fed the same kind of diet but with non-GM soy and corn instead.
Upon slaughter, a methodical autopsy found no differences in organ illnesses between both groups with two exceptions: stomach and uterus. GM-fed pigs had stomach inflammation much more commonly than the control group and also quite often more dilated uteruses:
... the median uterus weight of GM-fed pigs, as a proportion of body weight, was 25% higher than that of non-GM-fed pigs, which was statistically significant (p=0.025).
For non-GM-fed pigs, stomach inflammation was concentrated in the mild and moderate range, whereas GM-fed pigs showed much more severe inflammation (p=0.004). GM-fed pigs showed severe stomach inflammation at a rate of 2.6 times that of non-GM-fed pigs (95% confidence interval = 1.29-5.21) (Table 3). This occurred in both male (p=0.041) and female (p=0.034) pigs (Table 4). We found severe stomach inflammation in 22.2% of male pigs fed the GM diet and in 41.7% of female pigs fed the GM diet (compared to 5.6% and 18.9%, respectively, in pigs fed the non-GM diet (Table 4).
Maybe the most striking result of this study is that GM-crops do cause severe stomach inflammation in pigs at rates of 32% vs. 12% with a very high statistical significance: p=0.004!
Therefore if you have stomach problems, you are probably better off not eating any GMOs, something difficult, as they are not labeled as such for human consumption because of the lobby's pressure.