Tincup and TeresaB, thanks for the info and references. In particular, the American Journal of clinical Nutrition article from 1990 seems to be the source. Here are two abstracts from the journal (unfortunately the full article is behind a paywall).
Am J Clin Nutr. 1990 Jun;51(6):1020-7.
Effects of shellfish consumption on lipoproteins in normolipidemic men.
Childs MT1, Dorsett CS, King IB, Ostrander JG, Yamanaka WK.
Eighteen normolipidemic males were fed six different species of shellfish; each shellfish was fed so that protein in shellfish equalled that in animal foods in the normal diet, with less than one-half of the amount of fat in animal foods allowed for preparation of the shellfish. Oyster, clam, crab, and mussel diets, low in cholesterol and high in n-3 fatty acids, lowered VLDL triglycerides and cholesterol and, except for the mussel diet, LDL and total cholesterol. Squid and shrimp diets, higher in cholesterol and lower in n-3 fatty acids, did not change the blood lipids. The ratio of LDL to HDL cholesterol was decreased on the oyster and mussel diets. Oyster, mussel, and squid diets increased HDL2 cholesterol. Cholesterol absorption was decreased on the oyster, clam, and mussel diets. When consumed with moderate dietary fat restriction, oysters, clams, mussels, and crab appear to be useful in hypolipidemic diets for normolipidemic men.
Effects of shellfish consumption on lipoproteins in normolipidemic men
Marian T. Childs, Carol S. Dorsett, Irena B. King, Joyce G. Ostrander and William K. Yamanaka
American Journal of Clinical Nutrition. 51.6 (June 1990): p1020.
Cardiovascular disease has been linked to diets high in saturated fats and cholesterol. The inclusion of shellfish in diets meant to reduce risk of heart disease is controversial, although shellfish are very low in fat, which is believed to be beneficial. Molluscan shellfish (oysters, clams, squid, and mussels) have a large sterol content, but only one-third of the sterols are cholesterol, while crustaceans (shrimp, crabs) contain more cholesterol. The effects of diets rich in individual types of crustaceans or mollusks on plasma lipids (fats) of 18 men with normal plasma lipids were evaluated. The levels of animal-derived proteins and fats were strictly controlled on these diets. None of the shellfish caused increases in plasma cholesterol levels. All of the shellfish except shrimp and squid modified at least two of the blood lipids in ways which are considered to be beneficial. Oyster, clam, mussel, and crab diets were low in cholesterol and high in n-3 (omega-3) fatty acids, which may have health benefits. These diets lowered the levels of VLDL (very-low-density-lipoprotein) triglycerides and cholesterol in the blood. Additionally, all of the above except the mussels lowered total cholesterol and its subfraction, LDL (low-density-lipoprotein) cholesterol. Squid and shrimp diets were higher in cholesterol and lower in n-3 fatty acids, and had no effect on blood lipids. The ratio of LDL to HDL (high-density-lipoprotein) cholesterol decreased significantly in response to oyster and mussel diets, which is thought to be beneficial. Cholesterol absorption from the digestive tract was decreased by oyster, clam, and mussel diets, and this was related to the high levels of non-cholesterol sterols in these mollusks. A subfraction of HDL, HDL2, increased on the oyster, mussel, and squid diets; this is thought to be a healthy change but the reason for it is unclear. The study suggests that mussels, oysters, clams, and crabs are suitable for a diet designed to lower serum lipid levels, while shrimp could not be recommended, and squid should be excluded as well. (Consumer Summary produced by Reliance Medical Information, Inc.)
I believe the point of this 1990 study of 18 normolipidemic men (can't tell their ages from the abstract) was to indicate that certain shellfish (but not all) would not adversely affect lipoproteins, and thus could be considered to be ok and perhaps beneficial for patients who were on cholesterol lowering diets.
There was no reference to APOE status, and I am guessing that the same study on 50-70 year old apoe 4/4 and 3/4 adults with varying starting points for their lipids might show different results.
So my takeaway is that certain shellfish (mussels, oysters, clams, crab) are not on the "no" list with respect to lipoprotein components and may in fact be beneficial in men with normal lipoproteins. I'm not sure I would make these shellfish my main source of animal protein of choice based on this study, however. But I wouldnt avoid them. A different recommendation than Bredesen's SMASH (wild salmon, mackerel, anchovies, sardines, herring).
Thanks for the leads, I was just wondering where the recommendation came from, and now I know.
69 year old 4/4