In fact, there is evidence they can be harmful on both counts. Gene manipulation and crossbreeding are not the same process. The insertion point of genes, some from unlike biological sources, eg an animal gene transplanted into a plant, is random. Thus, cell metabolism may be disturbed in unpredictable ways with each new version of a GM product, even though the gene being inserted is the same. Human allergy testing, both short and long-term, is necessary.
Animal tests are also unsuitable.
Because of the complexities involved, we may never be able to properly test GM foods for safety. GM foods have so far proven to be poor performers economically A report by Dr Charles Benbrook, former Executive Director of the Board on Agriculture for the US National Academy of Sciences, found Roundup Ready Soy less profitable than conventionally bred varieties. The food resources of the world are abundant rather than scarce according to Peter Rosset, director of Institute for Food and Development Policy in California . It's a complex issue, sometimes clouded by controversy and emotion. ChB. PhD. FRCPath.