Though estimates of human longevity before the Industrial Revolution should be viewed with caution, it appears that the Knights Templar, a religious military order holding sway for nearly two centuries during the Middle Ages, lived exceptionally longer lives than their contemporaries. While generally attributed to divine providence, a more recent conjecture has suggested that strict adherence to the order’s lifestyle precepts, particularly around diet, was the key factor. And an exemplary diet it was: meat limited to three days weekly; low-to-moderate amounts of wine during meals; and fruits, vegetables, pulses, cheese, olive oil … and seafood … all in copious amounts. The intrepid Templars even tried their hand at aquaculture.
The legendary Ancel Keys and Seven Countries
The possible benefits of the Mediterranean-type diet enjoyed by the knights would not come under scrutiny until much later, largely beginning with the ground-breaking work of Ancel Keys, an American physiologist. Two puzzles intrigued Keys shortly after World War II: the decrease in coronary artery disease in Europe and the epidemic of myocardial infarctions among American executives.
Suspecting food was a factor in both cases he embarked on a series of pioneering epidemiological studies which looked at dietary habits and cardiovascular disease (CVD), eventually culminating in a major research project – the so-called Seven Countries Study – the results of which were published in 1970. The conclusion was clear: dietary levels of saturated fats correlate with blood cholesterol and heart attacks, all of which were lower in Japan and the Mediterranean region.
The “Eskimo diet”
At around the same time as Keys and colleagues were finalizing their landmark study, anecdotal reports of a low incidence of coronary heart disease in the Inuit of Greenland were surfacing. Danish physicians, upon investigating, speculated that the “Eskimo diet” of large quantities of high-fat whale and seal meat – and specifically their content of omega-3 polyunsaturated fatty acids (PUFAs) – was responsible.  
It turned out, however, that the real reason behind the reportedly lower rates of heart disease were gaps in Greenland’s health statistics, a result of the considerable logistical difficulties associated with monitoring a region of many isolated and far-flung communities. Indeed, as subsequent studies showed, the prevalence of CVD in Inuit – whether from Greenland, Canada or Alaska – paralleled that of their non-Inuit counterparts.  
Fish oils and human health
Nonetheless, the Eskimo diet studies launched extensive investigations into marine-sourced omega-3 PUFAs (the other nutritional components of seafood were largely ignored), and facilitated the development of a billion dollar nutraceutical industry around fish oil as a dietary supplement.  Two of those omega-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are found in seafood, the only major source for humans; and research in the intervening years has provided compelling evidence that EPA and DHA – particularly when consumed via seafood – can provide critical health benefits. 
But curiously, and for reasons that are currently unclear, there is limited scientific support for health benefits of omega-3s derived from marine oil supplementation      — for which it is typically marketed – nor any clear evidence for an effect during pregnancy on the outcome of children’s neurodevelopment and growth.     Likewise, systematic reviews show little evidence, for example, that supplementation during pregnancy and/or lactation reduces childhood allergies or favorably affects child adiposity, or that supplemented formula provides clear longterm benefits to preterm infants.
The benefits of seafood
In contrast with fish oil supplementation, however, scientific support for the benefits of seafood consumption is substantial. Large cohort studies, systematic reviews and/or meta-analyses have shown, for example, that:
- about 1-2 servings per week during pregnancy compared to no seafood intake correlates with enhanced neurodevelopment in children; 
- low or moderate fish consumption (1–4 servings/week) decreases the risk of mortality from coronary heart disease;    
- increasing fish consumption is associated with increasing prevention of acute coronary syndrome;
- omega-3 PUFA intake via fish consumption is associated with a lower risk of breast cancer;
- consumption of 60 grams (2 ounces) of fish per day compared to no seafood intake is associated with a reduction in all-cause mortality.
Though there is a wide variation in the nutritional characteristics between and among fish and shellfish species, seafood contains calories and proteins with high biological value along with essential nutrients (e.g., vitamins A, D, E and B12, zinc, selenium, iodine, taurine, and the aforementioned omega-3 PUFAs), many with well-established health benefits and necessary for optimum fetal development in pregnancy.      For some segments of the population, seafood is also an important source of vitamin D and iodine. 
Seafood and diet
The work of Ancel Keys, who went on to become a huge proponent of Mediterranean-type diets, laid much of the groundwork that has ultimately led to widespread expert agreement that diet – as the Knights Templar seem to have suspected – is important in promoting health and preventing disease and, further, that seafood is an integral component of a dietary regime associated with good health.  In this regard, it may not be an accident that Japan, one of the world’s top consumers of seafood, has the highest reported life expectancy globally along with one of the lowest mortality rates from heart-related diseases.
The scientific consensus around seafood benefits has led many governments via food-based dietary guidelines to recommend at least two servings of fish per week for older children, adolescents and adults to ensure the provision of key nutrients. Still, restrictions on consumption of a few select species due to contaminants, such as mercury, are still required, especially by sensitive populations. For most, however, and as shown by numerous studies, the benefits far outweigh the risks.
The value of seafood, ultimately, has perhaps been most eloquently expressed by fisheries and aquaculture researchers, Albert Tacon and Marc Metian, in a recent publication:
In a world where nearly 30% of humanity is suffering from malnutrition and over 70% of the planet is covered with water, aquatic foods represent an essential component of the global food basket to improve the nutrition, health, and well being of all peoples.
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