This study found that some of the most commonly eaten shellfish, including oysters, crabs, clams, shrimp and
mussels, showed no evidence of raising cholesterol levels. Crab and clams actually lowered the LDL levels (bad cholesterol). Mussels and oysters also lowered LDL, while raising HDLs. Fish and seafood contain a small amount of cholesterol, but are also rich in healthy, unsaturated fat and low in saturated fat, the type of fat that tends to raise blood cholesterol..