An Underrated Fish With Low Mercury Level Has More Omega-3s Than Walnuts

Eating more fish can do a lot for your health, thanks to its omega-3 fatty acids. Fish is also a great option if you're trying to lower your cholesterol since it's lower in saturated fat than meat and some types of poultry. The Dietary Guidelines for Americans recommend eating fish twice a week.

So why not eat more than that? Fish can contain varying levels of mercury, which may harm your kidneys, nervous system, and even your skin. While mercury is naturally occurring, industrial pollution adds more of it to the air. When it settles into bodies of water, fish absorb it into their systems — especially larger fish that eat smaller ones.

Shrimp, light tuna, and salmon are some of the healthiest types of fish, but you might also want to give herring a try. According to the U.S. Food and Drug Administration, herring averages just 0.078 ppm of mercury. A 143-gram Atlantic herring fillet packs in 2.98 grams of omega-3s — slightly more than the 2.5 grams in an ounce of walnuts.

Mercury made its way into our food systems through both agriculture and industry, according to a 2003 article in The Journal of Nutrition. Methyl mercury was used on farms in the early 1900s to destroy fungi that could cause disease. Mercury poisoning was rare but did occur among some factory workers, who experienced numbness, difficulty walking and talking, and vision and hearing loss. It wasn't until the mid to late 1900s that outbreaks of mercury poisoning were traced to people eating bread made from contaminated wheat.

One factory that used mercury ended up polluting the ocean with the byproduct methyl mercury, and people living nearby who ate a lot of fish began developing neurological problems. It took years before researchers discovered how mercury builds up in the food chain and accumulates in humans over time.

Yet some nutrients found in fish may help limit mercury's damage, especially in an infant's developing brain. The omega-3 fatty acid docosahexaenoic acid (DHA) is vital for building brain cells, and when a mother eats a DHA-rich diet, she can pass the nutrient to her baby through breast milk. Herring contains 1.6 grams of DHA. Iodine is another brain-boosting nutrient found in fish that supports healthy brain development.

Iron is important for attention, movement, and learning, and herring has 2 milligrams (11% of an adult's daily value) of iron. Choline, a nutrient often found in egg yolks, supports memory and helps protect the brain from harmful substances. Herring provides 22% of your daily choline needs.

The omega-3s in herring aren't just good for your memory and brain development. According to a 2008 article in Bioscience Hypotheses, omega-3s may play a role in improving mental health. While mental health is often associated with brain chemicals, some researchers suggest it may also be linked to poor blood flow to the brain and issues with the brain's protective barrier. Omega-3s may help by improving circulation and reducing inflammation, which supports both blood flow and the integrity of the blood-brain barrier. (Here are some other foods rich in omega-3.)

To protect your brain as you age, it's important not to skimp on fish. A 2018 article in the Annual Review of Food Science and Technology found that low intake of omega-3s is linked to a higher risk of cognitive decline and neurodegenerative diseases like Alzheimer's. Omega-3s improve nerve signaling and help maintain membrane flexibility in the brain.

Herring can also benefit your overall health. Omega-3s support heart health by lowering triglycerides and relaxing blood vessels. Replacing saturated fats with fish like herring may reduce your risk of dying from coronary heart disease. There is also some evidence that omega-3s may help lower the risk of certain cancers by slowing tumor growth and promoting cancer cell death, although research findings are mixed.