Fish really is brain food

Everyone has heard that eating fish is good for the brain. This notion goes back at least a century; the famous humorist and novelist P.G. Wodehouse often mentioned it in his books. In one scene, after Jeeves (the butler) describes a clever scheme to escape a ticklish problem, Bertie Wooster reacts:

I stared at the the man.
'How many tins of sardines did you eat, Jeeves?'
'None, sir. I am not fond of sardines.'
'You mean, you thought of this great, this ripe, this amazing scheme entirely without the impetus given to the brain by fish?'
'Yes, sir.' [From Very Good, Jeeves, (c) 1930 by P.G. Wodehouse]

A century ago, the evidence that fish is brain food was virtually nonexistent. Researchers have been looking at this question ever since, and the evidence has been mixed. Even if fish is good for the brain, the mercury content in some fish might have the opposite effect.

A new study that appeared last week in JAMA answers this question: fish is indeed good for the brain. More precisely, eating fish regularly was associated with a reduced risk of Alzheimer's disease. This benefit occurred despite the fact that people who ate more fish did have higher levels of mercury in the brain. Apparently, the levels of mercury were too low to cause harm, and the benefits of eating fish easily outweighed any risks.

The new study, by Martha Clare Morris and colleagues at Rush Medical Center in Chicago, looked at 554 Chicago residents, all part of a long-term aging study, who died over a ten-year period. The scientists conducted autopsies to look directly in the brain for physiological changes such as neuritic plaques, which are signs of Alzheimer's or other disease. They used questionnaire data, which they collected for everyone in the study, to measure how much fish people had been eating–an imperfect way to measure eating habits, but it's often the only realistic way to gather this information.

Here's what they found: people who ate seafood at least once per week had lower levels of three different physiological signs of Alzheimer's, but only in people with a genetic marker known as APOE ε4, which itself carries an increased risk of Alzheimer's. (None of the people in the study had dementia when they first enrolled, starting in 1997.) Somehow, then, eating fish seems to counteract the effects of this harmful genetic mutation.

Bad news for fish oil supplement makers: the study found that "fish oil supplementation had no statistically significant correlation with any neuropathologic marker." In other words, people who took supplements got no benefit. You just have to eat fish.

This isn't the first study to show a positive benefit to brain health from eating fish. The authors cite 13 previous studies that reported "protective relations between seafood consumption and n-3 fatty acids with cognitive decline and incident dementia." The JAMA study is the first to include mercury levels, brain changes associated with Alzheimer's, and diet all in the same study. It's reassuring to learn that despite the increased mercury caused (probably) by eating more fish, the overall effect is beneficial.

The authors also pointed out that as we age, our brains lose DHA, a critical lipid in the brain, and that therefore "fish consumption may be more beneficial with older age." The FDA already recommends that pregnant women and young children eat more fish for its nutritional benefits. Now there's evidence that older people should eat fish regularly too.

So it seems that Wodehouse's character Bertie Wooster might have been right: fish really is brain food.

Those fish oil supplements might cause cancer

Eating fish is good for you, especially fish that contain omega-3 fatty acids.  So I was surprised last week to read a new study in the Journal of the National Cancer Institute that found that omega-3 fatty acids increase the risk of prostate cancer.  The risk for both high-grade and low-grade cancer was increased with higher levels of omega-3 fatty acids.  This is a carefully done study, and the results should make anyone who is taking fish oil pills reconsider.

One reason this study caught many people off guard is that there has been much evidence showing that a diet rich in fish that contain omega-3 oils is good for you.  The Mayo Clinic says that  "eating fish helps your heart", especially fish like salmon that contain omega-3 fatty acids.  The American Heart Association (AHA) elaborates:

"Omega-3 fatty acids benefit the heart of healthy people, and those at high risk of — or who have — cardiovascular disease. Research has shown that omega-3 fatty acids decrease risk of arrhythmias (abnormal heartbeats), which can lead to sudden death. Omega-3 fatty acids also decrease triglyceride levels, slow growth rate of atherosclerotic plaque, and lower blood pressure (slightly)."

This all sounds great.  Because of the evidence about the benefits of fatty fish, supplement manufacturers have been marketing and selling fish oil pills for years, with great success.  As I described back in 2010, GlaxoSmithKline even created a high-dose omega-3 fatty acid pill called Lovaza that has FDA approval.

But the evidence for that you can get the same benefit from supplemental omega-3 fatty acids — taking a pill, that is — is much weaker.  In fact, a large review published last year in the Journal of the American Medical Association found no connection at all between supplemental omega-3 and a lower risk of heart attacks, strokes, or death in general.  Other studies have reported similarly negative results.  So it appears that fish oil pills may not have any heart benefits.

And now, with this new study, we learn that supplemental fish oil might increase the risk of prostate cancer.

The bottom line: the AHA recommendations about eating fish are probably still good ones.  The AHA website says:

"We recommend eating fish (particularly fatty fish) at least two times (two servings) a week. Each serving is 3.5 oz. cooked, or about ¾ cup of flaked fish.  Enjoy fish baked or grilled, not fried." 

But popping a fish oil pill is not going to cut it. As we've seen before, supplements often fail to show the benefits that a healthy diet offers.  So save your money and stop buying those fish oil pills — and fire up the grill and throw on a few salmon fillets for this weekend's barbecue.