Rancid oil is not good for the body.
It may lead to:
Increased attack by free radicals
Lack of vitamin C and E
The body needs more antioxidants to minimize damage
Reduced liver function
Lack of fat in cell membranes
Cell death
Increased risk of blood clots
Premature aging
Natural and fresh fish oils have the greatest effect on health (Norwegian research- Rubin Report No. 196/2011) http://www.nofima.no/filearchive/lite-oksiderte-omega-3-oljer-og-potensielle-helsefordeler.pdf
Rancid/oxidized fish oil leads to cell death and lower virility in salmon. (Rubin Report No. 173/2009) http://www.rubin.no/images/files/documents/4642-173_konkurrransefortrinn_ferske_oljer.pdf