The Brain-Diet Connection

Fish really is brain food

Perhaps no other dietary component has received more attention in this area than the long-chain polyunsaturated omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Abundant in cold-water, fatty fish, they play a part in brain development, maintenance and protection that vindicates the old saw, “fish is brain food.”

Of the two, DHA gets more attention, thanks to its role as a structural component in the brain and its cells. It accounts for 40% of the polyunsaturated fatty acids (PUFAs) in the former, and 50% of the plasma membrane weight of the latter.

Karma Rabon-Stith, manager, scientific affairs, Martek Biosciences Corporation, Columbia, MD, suggests we think about DHA and brain health in terms of two “bookend” phases where the science is strongest: during early human development, and then for function and maintenance later in life. Regular metabolic and cellular turnover mandates a steady supply of DHA to replenish what’s lost, but our limited capacity to synthesize DHA from its short-chain omega-3 precursor alpha-linolenic acid (ALA) argues mightily for obtaining that supply from an external dietary source.

“The science has shown that, for the developing fetus, as well as the developing infant up to 1 to 2 years of age, DHA is crucial,” Rabon-Stith says. “What we’re also seeing is that DHA is a potential nutritional neuroprotective agent for normal age-related cognitive decline.” Perhaps most exciting, she says, is the growing agreement that DHA “does play a role in a significant reduction in the incidence of Alzheimer’s disease”—though scientists are still puzzling out the mechanism itself.

Growing smarter babies

Let’s start at the beginning. “We all know that, at that stage of life, the brain is growing very rapidly,” Rabon-Stith says. Even during the final three months of gestation, the burst of fetal brain, nerve and retinal cell development depends on sufficient supplies of DHA. “So, if we’re just thinking about things from the cellular perspective, it’s important to have quality structural materials” like DHA, she says.

During this late-gestation growth spurt, the fetus relies solely on its mother for DHA, the only omega-3 that passes through the placenta from mother to fetus. “So, it’s important for pregnant women to make sure that they have the appropriate amounts of DHA for this development that is occurring,” Rabon-Stith says. “Just looking at the literature and the research in terms of levels,” she says, “at a minimum, there’s an EU consensus that pregnant and nursing women should get at least 200 mg DHA per day for perinatal infant development.”

Once the baby is born, the need for ready-formed dietary DHA continues, as the infant’s developing metabolism can’t yet synthesize enough of the fatty acid itself. Breast milk fulfills the baby’s needs, but infant formulas now also feature DHA fortification. Because no DHA reference daily intake (RDI) for babies yet exists, formulas may contain anywhere from 10 mg to 20 mg per 100 calories.

Another critical period for DHA consumption comes as babies transition to solid foods. At this stage, they’re at greatest risk for a significant decrease in DHA intake for a number of reasons. “One, when we think of most of the foods that naturally contain DHA—eggs, fish—the pediatrician is telling the mom to wait a couple of years because of food allergies,” Rabon-Stith says. Or, she adds, “the kids don’t really like the foods.” Hence the need for foods supplemented with DHA “at a minimum” of 100 mg per day.

When researchers study babies who consume ample DHA, the results are striking. A 1998 study published in the journal Pediatrics (101(1):e9) not only associated breast-feeding with increases in a child’s cognitive ability and school performance, but it attributed those increases to the effects of breast milk DHA on neurodevelopment. That same year, researchers publishing in The Lancet (352(9,129):688-691) found infants fed DHA-supplemented formula for the first 4 months demonstrated problem-solving skills at 10 months that were superior to those of infants fed a formula without supplementation. Such skills, the researchers noted, often translate to higher IQs later in childhood.

However, once we start looking at DHA benefits in later childhood and adolescence we see science in mid-evolution. “If we think of that middle group—kids aged 8 to 12 or 13—we see a lot of research being done to look at their cognitive performance,” Rabon-Stith says. “And the state of the science there is a growing area, too—really to look in and clearly discern the mechanism of action.”

What we can say amounts to some mixture of reasoned deduction and common sense. “We know that low levels of DHA will result in a reduction of serotonin levels in the brain,” Rabon-Stith explains. “And that, in itself, is related to things such as depression and AD/HD. So at this point, it’s a matter of going from that knowledge platform to really discerning what the science is behind it—what’s the process, what’s the mechanism, what is occurring, and what role does DHA play?”

Aging gracefully

That leaves the other half of the bookend: old age. And, at this point, Rabon-Stith says, “a number of epidemiological studies have been done to look at the relationship between fatty-fish intake and decreased cognitive decline.” She cites a major U.S. study from 2005 that evaluated 3,718 subjects and determined those who reported eating at least one fish-containing meal per week experienced a 10% lower cognitive decline than those who ate no fish. Among those who ate two fish-based meals, the reduction in decline was about 13%.