Quick summary: Of 94 peer reviewed studies on health risks or nutritional assessments of GMO products published in English between 1980 and 2009, 41 studies had at least one author with an affiliation to an industry with a vested interest in the GMO product; 53 studies had no such author affiliation. Of these, all 41 of affiliated studies' conclusions were favorable to the GMO product; 12--or almost one quarter--of the 53 unaffiliated studies' conclusions were unfavorable to the GMO product.
[Calculation: 12/53=0.226x100 = 22.6%]
The authors of this paper located 94 peer reviewed studies on health risks or nutritional assessment of GM products, published in English between 1980 and 2009.
Other search criteria leading to these 94 studies include:
1. article topic "relates to a GM plant as a food or feed product or as an ingredient of a food or feed product."
2. study "considered consumption of the GMO product" to (1) measure biological response or (2) involved participant data or (3) was conducted in a natural environment
3. one point of the study must relate to health or disease
The authors found that of the 94 total studies that met their criteria:
41 studies had at least one author affiliated with an industry that had "a vested commercial interest in the product under research"
53 studies had no authors affiliated with industry
Analysis of the studies revealed that:
Of the 41 studies with an author affiliation, all 41 studies were favorable to the GMO product in question ("no statements were made that cast the product in a negative light" with other positive conclusions)
Of the 53 studies with no author affiliation, 39 studies were favorable, 12 studies were unfavorable ("no statements were made that cast the product in a positive light" with other negative conclusions), and 2 studies were neutral (inconclusive).
Johan Diels et al., "Association of financial or professional conflict of interest to research outcomes on health risks or nutritional assessment studies of genetically modified products," Food Policy 36, (2011): 197-203, doi:10.1016/j.foodpol.2010.11.016.