These essential fats found in fish are a reminder that healthy diets are about more than what we eat. Our nutrition also depends on the things our food eats. 05/29/2020
Many seafood lovers know that salmon and other fish are packed with omega-3 fatty acids. These nutrients are vital for our brains and bodies, but humans can’t make them on their own — they have to come from food.
So, where does our food get them?
For human health, the three most important types of omega-3 fatty acids are ALA, DHA and EPA. Our dietary supply of ALA, or alpha-linolenic acid, comes mostly from nuts, seeds and other plants. DHA, or docosahexaenoic acid, as well as EPA, or eicosapentaenoic acid, comes from animals, especially seafood like salmon. And taken together, these fats are essential for normal human growth and development.
However, as it turns out, fish also can’t make DHA or EPA on their own. They too must get fatty acids from their food.
In fact, omega-3s undertake a long journey all the way from the bottom of the oceanic food chain to get to us. And that journey is a vital lesson in why it’s not only important that we ourselves eat healthy foods; it also matters that the food we eat has access to a nutritional diet as well.
Where Omega-3s Come From
Some 70 percent of our planet is covered by oceans. These vast ecosystems are home to most life on Earth, and they’re supported by a rather humble class of creatures.
If you travel to the base of the marine food chain, you’ll find phytoplankton. Phytoplankton are microscopic, floating marine algae that exist in such vast quantities they can change the color of the ocean (Dutkiewicz et al. 2019).
Phytoplankton are crucial for life — they prop up ocean ecosystems and help make our planet habitable. The tiny organisms suck in carbon dioxide and pump out oxygen during photosynthesis, giving us the air we need to breathe.
But phytoplankton also use photosynthesis to provide Earth with another vital component for life: omega-3 fatty acids (Jónasdóttir 2019). Using photosynthesis, they generate the chains of carbon and hydrogen that we call omega-3s. These marine algae are the main producers DHA and EPA (Randall et al. 1990).
All around the world, phytoplankton are constantly being feasted on by small animals called zooplankton as well as other miniature creatures, like the tiny crustaceans known as krill, which are then eaten by ever-larger animals.
As the phytoplankton are eaten, the omega-3s in their bodies get channeled to everything higher up the food chain. The essential fatty acids eventually reach all manner of life that doesn’t eat much algae, like predatory fish, seabirds, whales and humans (Kang 2011).
The Things Salmon Eat
This natural food web also explains why wild-caught salmon is so reliably rich in omega-3s, while farmed salmon often varies significantly in fatty acid levels. In the wild, most young salmon eat insects and adult salmon eat a variety of fish and other small marine animals.
Wild-caught salmon spend years eating other wild species packed with EPA and DHA. So, by the time they’re caught, the fish are ready to pass along these polyunsaturated fats and their health benefits to humans.
That’s great for us because studies have shown that omega-3s support brain and eye function, reduce inflammation, prevent chronic diseases and more (Singh 2005) (Anderson et al. 1990) (Peter et al. 2013).
But farmed salmon — and other farmed fish — don’t always rely on this food chain. They’re kept captive in pens and fed a wide range of foods — the exact mix varies from fish farm to fish farm. Some farmed salmon are given feed made from small, wild-caught fish, offering abundant omega-3s.
But in recent years, the smaller fish used to make food for farmed salmon have gotten more expensive and harder to find. As a result, some farmed salmon are now given cheaper feed packed with vegetable oils, which contain different sorts of fatty acids — not all of which are as healthy (Khan et al 2017). Research reported on by the BBC in 2016 found that omega-3 levels in farmed salmon had dropped by as much as half in just five years.
These diets leave farmed salmon with higher levels of another kind of fatty acids, omega-6s. And while a certain amount of these are necessary for health, most Americans get far too many of them from soy oils used in deep-fat fryers or cheap baked goods. Omega-6s can increase the risk of heart disease and other health problems when not eaten in moderation (Simopoulos 2008).
Omega-3 Levels in Grass-Fed Beef
Surprisingly, these same lessons about the importance of food chains apply to cows, too.
Omega-3s are also found in beef, albeit at levels far lower than what’s in seafood. However, beef can still be an important source of fatty acids for the general public because many Americans eat so little fish.
Like other complex creatures, cows also can’t make their own omega-3s. Their fatty acids come from eating grass, which is rich in ALA omega-3s, but not DHA and EPA. But conventional livestock is fattened with grain feed before being slaughtered and processed. That means the animals are deprived of grasses and, in turn, these essential fats.
Grass-fed cows don’t suffer from the same omega-3 scarcity. A 2018 study found that milk from grass-fed cows has 150 percent more ALA omega-3s than conventional milk and 50 percent more than even organic milk. Other studies have also shown that a 3.5-ounce serving of grass-fed beef has twice as many omega-3s as conventional beef (Leheska et al. 2008).
Similar research done on chickens found that diets rich in insects, greens and grains significantly increased the ALA omega-3 levels found in the animals’ meat and eggs. (Trebunová et al. 2007) And a 2019 study of 75 pigs found that grass-fed pigs had higher levels of omega-3s, as well as healthier omega-3/omega-6 ratios, than those fed more conventional diets. Of course, the ALA fatty acids found in beef, chicken and pork are much easier to get from plants.
But the more researchers look, the more evidence they find that healthier animals make for healthier food for us. It’s a powerful reminder that we’re not just what we eat, we’re also what our food eats.
Anderson GJ, Connor WE, Corliss JD. Docosahexaenoic acid is the preferred dietary n-3 fatty acid for the development of the brain and retina. Pediatr Res. 1990;27(1):89‐97. doi:10.1203/00006450-199001000-00023
Dutkiewicz, S., Hickman, A.E., Jahn, O. et al. Ocean colour signature of climate change. Nat Commun 10, 578 (2019). https://doi.org/10.1038/s41467-019-08457-x
Jónasdóttir, S. H. (2019). Fatty acid profiles and production in marine phytoplankton. Marine Drugs, 17(3), . https://doi.org/10.3390/md17030151
Kang JX. Omega-3: a link between global climate change and human health. Biotechnol Adv. 2011;29(4):388‐390. doi:10.1016/j.biotechadv.2011.02.003
Khan KU, Zuberi A, Fernandes JBK, Ullah I, Sarwar H. An overview of the ongoing insights in selenium research and its role in fish nutrition and fish health. Fish Physiology and Biochemistry. 2017;43(6):1689-1705. doi:10.1007/s10695-017-0402-z
National Institutes of Health. Office of Dietary Supplements. Omega-3 Fatty Acids: Fact Sheet for Consumers. https://ods.od.nih.gov/factsheets/Omega3FattyAcids-Consumer
Peter S, Chopra S, Jacob JJ. A fish a day, keeps the cardiologist away! - A review of the effect of omega-3 fatty acids in the cardiovascular system. Indian J Endocrinol Metab. 2013;17(3):422‐429. doi:10.4103/2230-8210.111630
Randall D, Liana B, Agradi E. Fish in human nutrition research and the implications for aquaculture. Ambio. 1990;19:272–275.
Singh M. Essential fatty acids, DHA and human brain. Indian J Pediatr. 2005;72(3):239‐242.
Simopoulos A. The omega-6/omega-3 fatty acid ratio, genetic variation, and cardiovascular disease. Asia Pac J Clin Nutr. 2008;17(S1):131-134. doi: 10.1684/ocl.2010.0325
Trebunová A, Vasko L, Svedová M, Kastel' R, Tucková M, Mach P. The influence of omega-3 polyunsaturated fatty acids feeding on composition of fatty acids in fatty tissues and eggs of laying hens. Dtsch Tierarztl Wochenschr. 2007;114(7):275‐279.