What Fish Does to Your Brain By James Hamblin

Have you ever considered undergoing brain-thickening surgery, only to find that such a thing does not exist? And that the guy in the van was probably not actually a surgeon? Well, consider fish.

Dr. Cyrus Raji, a resident radiologist at UCLA, appreciates value far beyond the cosmetics of a thick cerebral cortex. He's the lead researcher in a new study in the current American Journal of Preventive Medicine that found that people who regularly eat fish have more voluminous brains than those who do not—in such a way that should protect them from Alzheimer's disease.

"Understanding the effects of fish consumption on brain structure is critical for the determination of modifiable factors that can decrease the risk of cognitive deficits and dementia," Raji and colleagues write. The team has previously shown gainful effects of physical activity and obesity on brain structure.

This study found that eating fish—baked or broiled, never fried—is associated with larger gray matter volumes in brain areas responsible for memory and cognition in healthy elderly people.

People who eat fish at least once a week have larger
gray matter volumes in the red/yellow areas.
(Raji et al., American Journal of Preventive Medicine)

"There wasn't one type of fish that was the best," Raji told me by phone, probably while eating fish. "All that mattered was the method of preparation." Fried fish had a unique dearth of benefits to the human brain.

"If you eat fish just once a week, your hippocampus—the big memory and learning center—is 14 percent larger than in people who don't eat fish that frequently. 14 percent. That has implications for reducing Alzheimer's risk," Raji said. "If you have a stronger hippocampus, your risk of Alzheimer's is going to go down." 

"In the orbital frontal cortex, which controls executive function, it's a solid 4 percent," Raji said. "I don't know of any drug or supplement that's been shown to do that."

Speaking of supplements, the researchers initially looked to omega-3 fatty acids as the driver of these benefits. But when they looked at the levels of omega-3s in people's blood, it didn't correlate with better brain volumes. 

"These findings suggest additional evidence that it is lifestyle factors—in this case, dietary intake of fish," the researchers write, "and not necessarily the presumed biological factors that can affect the structural integrity of the brain."

Omega-3 fatty acids have previously been shown to slow cognitive decline. In one study, higher levels of omega-3 fatty acids in one's blood were associated with lower rates of brain atrophy observable over just a four-year period. We also know that when rats are fed diets low in omega-3 fatty acids, they have increased signs of dementia, possibly mediated by insulin and related buildup of amyloid plaques in their tiny brains. 

Eating more omega-3 fatty acids, a lot of fruit, and not much meat, has previously been associated with increased volume throughout the brain's gray matter. Recent research ins the journal Neurology found that elderly people with high levels of omega-3 fatty acids in their blood had better cognitive function than those with lower levels. MRIs of their brains showed larger volumes, as well. (The associations also held for vitamins B1, B2, B6, B12, C, D, and E, and folate.)

Drs. Deborah Barnes and Kristine Yaffe at the University of California at San Francisco recently calculated in Lancet Neurology that up to half of cases of Alzheimer's disease "are potentially attributable" to seven modifiable risk factors: diabetes, midlife high blood pressure, midlife obesity, smoking, depression, cognitive inactivity or low educational attainment, and physical inactivity. Minimal inroads in those areas, they say, could result in millions fewer cases of Alzheimer's.

Researchers at the University of Pittsburgh School of Medicine corroborate, "Our research has consistently shown that it is the interactions among these risk factors with the patho-biological cascade of Alzheimer's disease that determine the likelihood of a clinical expression as dementia or mild cognitive impairment."

Other suspects in the fish-brain benefit paradigm are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which seem to increase the size of the amygdala and anterior cingulate gyrus, and possibly overall brain volume. DHA and EPA can affect the way neural synapses fire. 

"Something about fish consumption, whatever it is, is strengthening to the brain," Raji said. "It's also possible that we're capturing a general lifestyle effect—that there's something else out there we're not measuring that's accounting for this."

For one, people who ate fish might also eat more tartar sauce, and it might actually be that tartar sauce was responsible here. Though that's unlikely. The researchers did control for obesity, physical activity, education, age, gender, race, and every other variable they could think of, and fish-eating itself remained a strong predictor of gray matter volume. 

The number of people with dementia is projected to double every 20 years. Or, as Raji put it to me, "By the time you and I are in our 60s and we start worrying about Alzheimer's disease, 80 million people in the United States are going to have it." 

He and other dementia researchers note that the challenge is to implement prevention strategies in the decades prior to the ages when dementia manifests; before there are any signs of brain structural or functional abnormalities. But it doesn't have to me a foundational life overhaul. People who ate fish once per week were just as well off as those who ate it more frequently.

"Nobody wants to eat food like they're taking medicine," Raji said. Unless, of course, they do.