compelling reasons to stay away from franken foods
Have you heard the term GMO: Genetically Modified Organism? It refers to a technique of infusing different species genes into another species. An example of this, is taking genes from the white flounder fish and adding them to a tomato, in attempts to make the plant resistant to bacteria. At the superficial level, the outcome can be a heartier plant, however this process has numerous ramifications to the farming industry, and to our health. A great documentary that explains more about the subject, is The Future of Food.
In reality our food is our medicine, and with this type of altering we don't really know what we are getting when we purchase food. However, there is hope, there are upcoming propositions in state legislation in America that would require labeling of such foods. This way, consumers can make a fair and informed decision about what they are putting into their bodies. The European Union, amongst a few other countries started this back in 2004.
The GMO issue can go beyond food though, and into vitamins and supplements. Many vitamins are often derived from food sources, which can have been genetically modified. Vitamin C is often made from corn and Vitamin E from soy. Both of these crops of often GMO. Contrary to the thoughts that went into the GMO industry, the crops actually often require more pesticide use and do not increase the yield. Further they are not safe for our bodies and our land. 
You can educate yourself further at http://responsibletechnology.org/ . If you need help when your at the grocery store, there is an app and/or printable guides available at http://nongmoshoppingguide.com/ .
The most simplistic way is to buy organic and then you know that it is non-gmo.