As soon as they adopted white flour and sugar as dietary staples, the tooth decay prevalence of Polynesian groups went as high as 33.4% of teeth, or about 11 cavities per person. This represents a 5,600% increase in the prevalence of tooth decay. The next generation to be born also suffered from characteristic facial and skeletal abnormalities that are common in modern societies to varying degrees.
This leads me to ask the question, what is unique about seafood that allows it to support excellent development and maintenance of the human body? Seafood has a lot of advantages. It tends to be very rich in minerals, particularly iodine which can be lacking in land foods. It's also a good source of omega-3 fatty acids and low but adequate in linoleic acid (omega-6). This impacts development and maintenance in a number of ways, from fat mass to dental health.
As I wrote in the last post and others, I believe that one of the major determinants of proper development and continued health is the diet's content of the fat-soluble vitamins A, D and K2. K2 in particular is rare in the modern diet. We're also deficient in vitamin D because of our indoor lifestyles and use of sunscreen. Polynesians didn't have to worry about vitamin D because they spent much of the day outside half naked.
How about K2? Is seafood a good source? At first glance, it doesn't appear to be. Mackerel is the best source I came across on NutritionData, with one serving delivering 5.6 micrograms of vitamin K. It wasn't specified, but only a portion of that will be vitamin K2 MK-4, with the majority probably coming from K1. Most other types of fish have very low levels of vitamin K.
But we have to probe deeper. Nutrition information for fish refers to muscle tissue. Muscle is a poor source of K2 in mammals, could that be the case in fish as well? It turns out, the organs are the best source of K2 MK-4 in fish, just as they are in mammals. It's most concentrated in the liver, kidneys, heart and gonads. This loosely resembles the situation in mammals, which also retain MK-4 in their kidneys and gonads (along with pancreas, salivary glands, and brain).
I don't know how frequently traditional non-industrial cultures ate fish organs. My guess is they discarded most of them as do modern cultures, because they smell funny and putrefy rapidly. There are some exceptions, however. Certain traditional cultures ate fish livers, cod for example. Price described a dish eaten by a healthy, isolated Gaelic group in Nutrition and Physical Degeneration:
An important and highly relished article of diet has been baked cod's head stuffed with chopped cod's liver and oatmeal.Gonads are one of the richest sources of K2 MK-4 in fish, containing 5-10 micrograms of MK-4 per kilogram of tissue in a few different species (according to this paper). Even that is not really an impressive concentration.
One thing that is universally relished by traditional groups is fish eggs, which of course develop from the gonads. A number of cultures dried fish eggs, sometimes trading them far into the interior. Although they haven't been analyzed for MK-4 content in modern times, Price found fish eggs to be a rich source of K2. Speaking of vitamin K2, he said: "its presence is demonstrated readily in the butterfat of milk of mammals, the eggs of fishes and the organs and fats of animals". Unfortunately, Price's assay was not quantitative so we don't have numbers.
As mainstream medicine slowly catches up to the importance of vitamin K2 MK-4 that Price described in the 1940s, more foods are being tested. I think we'll see values for fish eggs in the near future. This will allow us to discriminate between two possibilities: 1) seafood is a good source of K2, or 2) the human requirement for K2 is not particularly high in the context of an otherwise healthy diet.