Want to live longer? You need this nutrient

The rise of humanity
Stephen Cunnane, Ph.D., is an ideal poster boy for a high omega-3 diet. Tall, energetic, and trim, this researcher in brain metabolism at Quebec's University of Sherbrooke lacks any sign of the paunch you might expect in a man of 55 years. His secret, he confides, is lots of exercise and at least two servings of omega-3-rich fish a week.

Cunnane believes that omega-3s, and specifically DHA and EPA, are the crucial nutrients that permitted proto-humans with brains the size of a chimpanzee's to become chattering, tool-using Homo sapiens. DHA has a cylindrical shape and can compress and twist like a Slinky, switching between hundreds of different shapes billions of times a second. The molecule is particularly abundant in the tails of rattlesnakes, the wings of hummingbirds, the tails of sperm, and the retinas and brain cells of people who eat fish. A neuron that is high in DHA molecules is virtually liquid, allowing for more effective reception of serotonin, dopamine, and other crucial neurotransmitters. In test subjects, this heightened neuroplasticity has been linked to better vision and eye-hand coordination, better mood, enhanced general movements, and an increased capacity for sustained attention. EPA is no less crucial: It reduces blood clotting and dampens the inflammatory response in tissues. Such chronic inflammation is suspected to be at the root of most of the so-called diseases of civilization, from Alzheimer's and depression to heart disease and cancer.

While it's true that terrestrial plants are good sources of omega-3s, the fatty acid most present in land-based species is alpha-linolenic acid (ALA). Essential for good health, ALA can be found in fruits, vegetables, and some seeds, among them lettuce, leeks, purslane, kale, broccoli, blueberries, hemp, chia, and flaxseed. ALA is especially rich in plants that grow in intense light, and the fatty acid is thought to help the plants recover from sun damage. Though the human body is capable of turning ALA into DHA and EPA through a series of enzymatic reactions, it is not particularly good at it: Less than 1 percent of the ALA we get from vegetable sources ultimately becomes DHA and EPA. The ocean is the world's richest source of DHA and EPA, particularly from plankton-eating oily fish such as sardines, mackerel, and herring.

Recently discovered archaeological evidence suggests that around 2 million years ago, early hominids, the ancestors of modern humans, left the forests to live on the wooded edges of huge brackish lakes and estuaries in what is now Africa's Rift Valley. Prehistoric middens found in Kenya and Zaire are filled with shells and headless catfish skeletons, evidence that these proto-humans were taking full advantage of the easily gathered protein — and, incidentally, omega-3 fatty acids — at one of the world's first all-you-can-eat seafood buffets. Around the same time, hominid brains began to grow, swelling more than twofold from 650 grams in Homo habilis, the first tool-using hominid, to 1,490 grams in the early ancestors of Homo sapiens. "Anthropologists usually point to things such as the rise of language and tool making to explain the massive expansion of early hominid brains," says Cunnane. "But this is a catch-22. Something had to start the process of brain expansion, and I think it was early humans eating clams, frogs, bird eggs, and fish from shoreline environments."

Seafood is especially rich in the minerals zinc, iodine, copper, iron, and selenium, all of which are essential for fetal brain growth and good brain function in adults, and may have kick-started the process of explosive neural growth. This shore-based theory of early human evolution, laid out by Cunnane in his book Survival of the Fattest and championed by the British brain chemistry expert Michael Crawford, challenges the prevailing savannah and woodland theories, which pinpoint hunting and scavenging as the motive force in brain evolution. The Aquatic Ape Theory is a more controversial version of the shore-based scenario. Propounded by Sir Alister Hardy and Elaine Morgan in the United Kingdom, it seeks to explain such diverse phenomena as bipedalism and the streamlined human torso by positing an aquatic phase to human evolution, in which hominids spent a good percentage of their waking lives wading and swimming in search of seafood.

Cunnane's account has the advantage of explaining some of the more puzzling attributes of Homo sapiens. Why, for example, are we the only primates whose babies are born with more than a pound of subcutaneous fat, and whose fetuses actually float? And why, unlike elephants, rhinos, and other mammals whose brains actually shrank over the generations, did our ancestors' gray matter undergo explosive and sustained growth in the past 2 million years?

EPA and DHA, Cunnane insists, work in synergy; what is good for the heart also tends to be good for the brain. "Even if you don't change the composition of your brain by getting more DHA," says Cunnane, "the vessels are the things that supply oxygen and nutrients to your brain, and they require omega-3 fatty acids for optimal function as well. For blood pressure regulation, for controlling your platelet function, your clotting tendency, the rhythm of your heart, you need omega-3 fatty acids."

Cunnane shows me a photo of an image carved into buff-colored sandstone. "This was found in a cave in France. It must have been one of the Sistine Chapels of the drawing world at the time." It is a highly naturalistic rendition of a salmon, down to gill flaps and hooked mandible. Evidence of early fish eating, jaw-dropping in its technical sophistication, the image is 22,000 years old. An interesting footnote to Cunnane's theory is that our seafood-eating Cro-Magnon ancestors, including the master sculptor responsible for this bas-relief, might well have been smarter than we are. Fossil evidence shows that the Cro-Magnons, though their bodies were smaller than those of Neanderthals, had brains about 200 grams heavier than modern humans'. Humanity's relatively recent creep away from seafood-rich shorelines, Cunnane believes, explains everything from the 20 percent of American women who are iron deficient to the dangling goiters of people living in mountainous regions. (If iodine hadn't been added to table salt 80 years ago, cretinism, a deficiency typified by severely stunted mental growth, would be endemic in most developed countries.)

Until the American Revolution, 98 percent of the population lived along rivers and oceans. Leaving the coasts might be a slow-motion public-health disaster. Deficiencies of DHA and the brain-selective minerals abundant on shorelines, speculates Cunnane, affect the performance of the modern human brain and, uncorrected, might eventually cause brains to shrink.

"Adaptation will be necessary," he concludes in Survival of the Fattest, "either by making supplements more widely available or by moving back to the shorelines, or we will conceivably face evolutionary processes that could eventually reduce cognitive capacity."

In other words, our cod-liver-oil-loving grandmothers had it right: Fish really is brain food. And our disastrous decision to replace the omega-3s in our diet with omega-6s might be all the proof anybody needs that, as a species, Homo sapiens are getting demonstrably dumber.

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