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CHAPTER 1
A Short Natural History of Seafood
Fish, amphibian, and reptile, warm-blooded bird and mammal—each of us carries in our veins a salty stream in which the elements sodium, potassium, and calcium are combined in almost the same proportions as in sea water. This is our inheritance from the day, untold millions of years ago, when a remote ancestor, having progressed from the one-celled to the many-celled stage, first developed a circulatory system in which the fluid was merely the water of the sea.
—RACHEL CARSON, THE SEA AROUND US
IN THE SUMMER of 1935, the Inuit people of eastern Canada's remote Arctic inlets were still living a subsistence lifestyle. Clad in sealskin leather, they moved with the weather and the walruses, seals, and whales that they hunted. The only plants they ate were the blueberries that grew during 2 months of the year and sometimes the half-digested contents of caribou stomachs.
The fact that this nomadic hunter-trapper lifestyle persisted into the 20th century in one of the world's harshest environments is incredible. Perhaps even more unfathomable is the notion that the Inuits' restricted diet made them among the healthiest people in the world. But in the early 1930s, the Inuits had made contact with the modern world through the fur-trading Hudson's Bay Company, and the word was out that these tough Arctic people did not appear to suffer from diabetes, cancer, or arteriosclerosis.
Israel M. Rabinowitch, a chemist with McGill University, joined the Canadian government's annual supply trip to the Inuit communities in the summer of 1935 to find out if the stories about the hardy Inuits were true. Sailing aboard the HMS Nascopie, he traveled to four Arctic islands-- Southampton, Devon, Ellesmere, and Baffin—and made dozens of visits to towns that were nothing more than temporary assemblages of a few sealskin tents.
In total, Rabinowitch examined 389 Inuits. While the population wasn't quite as disease free as reputation had it, they were remarkably healthy. He found no diabetes. Only one possible case of cancer. A few calcified arteries. Teeth worn down by chewing leather to make clothes and tents. "If there was a serious health problem amongst the Eskimos, [I] was not aware of it," Rabinowitch noted in a report published in the Canadian Medical Association Journal in 1936. He didn't even mention heart disease.
How could a people living in such harsh conditions not report a single heart attack?
During flush times, the Inuits ate 5 to 10 pounds of meat a day. Rabinowitch estimated that an average person ate 30 to 40 grams of carbohydrates, 250 to 300 grams of protein, 400 to 600 milligrams of cholesterol, and about 150 grams of fat per day. One hundred fifty grams of fat is the amount in 33 Twinkies.
Of course, not all fat is created equal. Inuit people weren't eating Twinkies. They were eating fresh, usually raw meat from marine mammals, fish, and occasionally caribou with their bare hands, sometimes ending meals covered in blood and blubber. At the time of Rabinowitch's study, science had not yet discovered why this high-fat, low-carbohydrate diet was good for their health.
Later studies would confirm the incredible vitality of the Arctic peoples. In 1980, Danish scientists compared rates of myocardial infarction, asthma, diabetes, multiple sclerosis, and other health problems among Greenland's Inuit with those of Danes. The data cleaved neatly, with the healthier Inuits showing little to no instances of the diseases compared with the "civilized" Danes.
The scientists didn't take into account one of the oldest uses of seafood—treatment of disease—because knowledge of the techniques had been lost to history for more than a century. In 1770, a woman suffering from severe rheumatism arrived at the Manchester Royal Infirmary in England. At the time, the standard treatment for rheumatism included "rubbing of her joints with cod-liver oil," as reported by Maurice Stansby in the seminal text Fish Oils in Nutrition. The poor woman received no relief, and after a year she inquired whether she could ingest the oil instead. She was brave: In the 1700s, the oil was obtained by pressing rotting cod livers, and it was an opaque, vile-tasting liquid. "Although the hospital had no confidence that this would have any effect, she was allowed to [ingest the oil]," Stansby wrote. Her symptoms disappeared.
Unfortunately for the woman, her doctors ascribed her good health to the changing seasons, and she wasn't given any more cod-liver oil for a year—during which her rheumatism flared more severely than before. The hospital relented and gave her more oil, only to see her symptoms disappear yet again.
After that, the Manchester infirmary regularly prescribed 1 to 3 tablespoons of cod-liver oil taken up to four times a day to treat rheumatism. A Dr. Thomas Percival wrote up the case for the London Medical Journal in 1783. But the difficulty of obtaining the oil, coupled with the truly revolting flavor (sometimes it was mixed with peppermint, although it's hard to imagine that helped), caused fish oil to fall out of favor, and it was forgotten.
Seafood's role in heart health was discovered only after those early-20th-century studies on Arctic peoples. Soon, other indicators emerged suggesting that seafood was helpful in avoiding heart disease. Norway experienced a steep decline in fatal heart attacks during the German occupation of 1941 to 1945. In these years, Norwegians could not obtain much in the way of meat, eggs, or whole milk, and instead began eating more fish, skim milk, and cereals. After the war, Norwegians returned to their red-meat diet, and the rate of heart attacks rose again. Similarly, scientists began to notice that the Japanese, who eat up to 13 times as much seafood as Americans, had much lower rates of heart disease as well. One study found that the Japanese were 20 times less likely than Germans to die of heart attacks.
One of the landmark studies on seafood consumption and heart health took place in the Netherlands from 1960 to 1980. Over those 2 decades, scientists tracked a group of adult men from the town of Zutphen who ate a consistent amount of fish throughout their lives. The result? The more fish the men ate, the less likely they were to die of heart disease.
After the results of the Zutphen study were published in 1985, the knowledge of seafood's role in heart health went mainstream. Now, just about every authority from the American Heart Association to the World Health Organization recommends eating seafood at least twice a week.
So what is it that makes seafood so healthy?
It has to do with its molecular structure. Seafood is the premium source for essential omega-3 long-chain fatty acids. The human body cannot generate these fatty acids by itself, so they must be consumed.
Since the 1980s, "omega-3" has been a nutrition buzzword, found everywhere from margarine labels to fad diet cookbooks. It's usually mentioned along with its relatives, the omega-6 fatty acids, which are derived from plant oils like soybean, corn, palm, rapeseed (canola), and sunflower. Omega-3 fatty acids are found in some plants, like walnuts, but the best sources are fish and seafood. They, too, ultimately derive their omega-3s from plants--the phytoplankton that support all ocean life.
THE ABCS OF OMEGA-3S
Omega-3 fatty acids are made of a string of carbon and hydrogen atoms. "Saturated" fatty acids hold all the hydrogen atoms their structures allow. Sometimes certain enzymes can remove pairs of hydrogen atoms. "Monounsaturated" fatty acids have one fewer pair of hydrogen atoms than the saturated versions. The loss of the hydrogen pair creates a double bond between the adjacent carbons. When more than one pair of hydrogen atoms disappears, fatty acids with two or more double bonds are created. These are known as "polyunsaturated" fatty acids. Omega-3 fatty acids fall into this category. The "3" in their name comes from the fact that their first double bond is three carbons away from the end of the chain known as the omega end. (The other terminus is the acid end.)
There are numerous kinds of omega-3s, but only three that we usually hear about in nutrition. Alpha-linolenic acid (ALA) is the only omega-3 found in plants, like walnuts, chia seeds, and flax. ALA isn't easy for the human body to use, but it's often ALA that's in foods like margarine, cereal, bread, and snacks whose packaging proclaims heart-healthy omega-3s are inside.
The more important nutritional benefits that we get from consuming omega-3s come from two other types of omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These are found almost exclusively in marine sources and egg yolk, and yet they are critical to our health, having particular importance in fetal development and maintenance of brain, retina, heart, and immune system health.
FISH IS (HEART AND) BRAIN FOOD
The early study revealing that Greenland Inuits had little to no occurrence of diseases like myocardial infarction, asthma, and diabetes compared with Danes demonstrated two things: first, that Homo sapiens is not, on the whole, naturally given to these diseases, meaning that there are environmental forces at play. And second, that the high-fat diet of the Inuits correlated with their good health. The scientists found that the fish, seal, walrus, and whale diet of the Inuits—a diet that has nearly disappeared today because residents of remote communities now have access to as much processed, high-carbohydrate food as just about any big-city dweller—meant that about 14 percent of the fatty acids consumed by the Inuits were omega-3s. The Danes, meanwhile, were getting only about 3 percent of their fatty acids from omega-3s.
By the late 1980s, the link between omega-3s and heart health was firmly established. Scientists now agree that consuming omega-3-rich seafood two times a week can cut your chance of dying from a heart attack by 30 percent or more. Since then, scientists have explored other potential health benefits of omega-3s. Although not fully accepted by everyone, here are a few of the things that DHA and EPA omega-3 fatty acids may be able to do:
Raise HDL, or "good," cholesterol
Lower blood pressure
Reduce the risk of heart arrhythmias
Reduce the chance of forming blood clots that can cause heart attack or stroke
Discourage the buildup of arteriosclerotic plaque by inhibiting the growth of smooth muscle cells
Promote the resolution of inflammatory responses, resulting in faster healing from diseases and wounds
Reduce an infant's chance of developing allergies
Reduce the risk of depression, bipolar disorder, and suicide
Protect neurons and improve brain cell repair, especially in conditions of brain injury or oxidative stress
Lower the risk of Alzheimer's disease
Ensure correct function and development of neurons, especially during fetal and infant development and in neuronal cell damage (e.g., stroke)
Our need for omega-3s begins before birth. A developing fetus absorbs fatty acids from its mother; DHA and small amounts of EPA are present in breast milk. The price for insufficient DHA and EPA is high. Without the brain- boosting omega-3s, babies have a greater chance of developing learning disorders. In the past, infants were often given a teaspoon of cod-liver oil, which is flush with vitamins A and D in addition to omega-3s, every day. But it wasn't until 2001 that manufacturers began fortifying store- bought formula with DHA.
All these data on the importance of omega-3s raise two important questions. First, how can we afford to fish out the world's oceans when they're such important sources of great nutrition? The United Nations says that, worldwide, 87 percent of all wild fisheries are already depleted or maxed out under intense industrial fishing pressure (happily, US fisheries are doing somewhat better). Imagine a world where children and pregnant women cannot access the omega-3s that are the building blocks for healthy brain and body development. As fish become scarcer, they will become more dear, too, leaving the neediest families in poor countries even more nutritionally disadvantaged, broadening the gulf between the haves and have- nots. How we avoid such a fate--and we can--is the rest of our story. But for now, let's focus on the second question raised by the potency of omega- 3s: What quirk of evolution caused us land dwellers to develop such an affinity for a substance that comes from the oceans?
THE OCEANS PREDATE LIFE ON EARTH. Created by vast, thousand-year rains as Earth cooled, oceans—or really, one global, interconnected ocean—formed more than 4 billion years ago. The continents followed, born of Earth's erupting mantle. No one really knows where the first single-celled organisms appeared, but one common hypothesis places them in the hydrothermal vents of the deep sea.
While the continents remained barren, rock-strewn expanses, the oceans hosted blue-green algae that dominated life on Earth for more than a billion years. Through photosynthesis, the blue-green algae pumped oxygen into Earth's atmosphere until it reached a poisonous tipping point known as the Great Oxygenation Event, which killed off most life on the planet about 2.4 billion years ago. But the newly oxygenized atmosphere allowed other life forms to flourish. And so the oceans' dominant algae slowly gave way to multicellular organisms: sponges, jellyfish, squid, and trilobites. Fish, Earth's first vertebrates, appeared about 500 million years ago.
Algae likely colonized the shorelines long before any multicellular creatures climbed out of the waves. The first critter to venture up the beach 530 million years ago was probably a centipede-like creature scuttling along on dozens of feet. We can still see snapshots of evolution in the oceans: In 2010, scientists in Australia named nine new species of handfish with footlike protrusions instead of fins. Other ocean species are more like examples of arrested evolution. Some modern shark species have remained virtually unchanged over 100 million years, surviving even the extinction event that wiped out the dinosaurs.
For much of the last century, the accepted narrative for the evolution of early humanity has been what's called the savanna theory: The precursor of mankind, a species of great ape that lived in the trees of Africa, eventually moved down to the ground as the climate became hotter and drier. There, he scavenged for animals, berries, and fruits, eventually learning to hunt and walk upright. But life on the savanna, with its big cats and other predators, was more dangerous than it was in the trees. Marvin Harris, a prominent 20th-century anthropologist, spoke for many of his colleagues when he speculated that early humans were able to overcome the dangers of the savanna despite their lack of fangs or other natural weaponry by evolving the ability to use tools: "Those who brandish the biggest sticks are more to be feared than those who snarl with the biggest teeth." Coordination between hunters, and communication, speech, and culture, followed.
