Commercial pressure on GMO foods will aim to enhance various food traits:
- Enhanced shelf life.
- Resistance to certain weedkillers and strong pesticides.
- Enhanced production of natural pesticides.
- Enhanced yield (at the expense of something less vital, like height, or sterility)
However enhancing these traits is likely to also have undesirable consequences too:
- Enhancing shelf life has at least these components.
- Hiding visible signs of poor food quality. For example many vitamins break down over time, but this would not be obvious from visual inspection.
- Making the food 'indigestible' to bacteria. This is likely to make the food less digestible to humans too. For an extreme take on this see RyansWorld: Zero Calorie French Fries.
- Knocking out a plant's 'hypersensitive response' (the mechanism which makes leaves go yellow on damage or infection) is also knocking out a basic plant defense mechanism. Plants riddled with plant parasites are more likely.
- Resistance to certain agrochemicals will lead to greater use of these chemicals and destruction of beneficial interactions as well as the intended ones. One can presume that plant technologists will aim to preserve known good symbiotic interactions, such as the plant-root bacteria interaction that fixes nitrogen, and the plant-insect interaction that pollinates, but what about interactions which we are currently unaware of? There is also a question of 'how' does the plant achieve resistance? Soya bean for example moves dioxin (agent orange) into the edible part, away from more sensitive parts, so it gets concentrated in Soya oil. A plant that resists agrochemicals by breaking them down may have undesirable effects by also breaking down desirable compounds.
- Plants can be made to endogenously produce natural pesticides. Arpad Pusztai's paper's on the danger on this, suggest that the level of pesticide is not the only factor to take into account in assessing toxicity (to humans). Endogenously produced toxins may get modified or packaged in such a way as to be more damaging than a simple mixture would suggest.
- Enhanced yield at the expense of some other quality is potentially a danger if the gene escapes into the wild. Enhanced yield may also be in appearance only. Researchers trying to increase the yield of tomato pulp from tomato plants have had great difficulty in doing more than just increasing the water uptake of tomatoes.
- The transposable elements used to bring the foreign DNA into the plant genome may in themselves be dangerous, causing genetic damage to those eating the foodstuff.
- GMO potatoes may cause cancer.
- Probably loads of links available to anti GMO sites...