Fresh, wild-caught fish has been a staple of the human diet for tens of thousands of years. But today, as the global population stretches toward eight billion, an increasing demand for seafood has pushed many consumers to rely on farmed fish from grocery store freezers.
And as global stocks of wild salmon have decreased in recent decades, salmon farming has grown significantly. These operations have often been criticized for their negative environmental impacts. Some in the aquaculture industry have worked to improve the quality of their products, but farmed fish still generally have lower levels of some key nutrients and vitamins. In short, farmed salmon can’t compete with their wild counterparts when it comes to nutritional value.
Omega-3 to Omega-6 Balance
Wild salmon are healthy for us because of what they eat. Salmon are packed with omega-3 fatty acids, which are critical for cardiovascular and brain health. Our bodies can’t make omega-3s, so we get them from our diet. But wild salmon also get omega-3s from their diet thanks to what salmon eat, including marine organisms like shrimp and krill. These creatures pass along fatty acids that the salmon store in their tissues.
Farmed salmon are also rich in these healthy fatty acids. And eating them can be part of a healthy diet. In fact, studies have often shown that farmed salmon actually have more omega-3s than wild salmon, because their bodies are fattier overall. But with the good comes the bad.
The quality of food given to farmed fish can vary significantly, with many raised on diets rich in vegetable oils. And when farmed fish are raised on diets of non-marine feed, they have higher levels of less-healthy compounds like omega-6 fatty acids. Omega-6s are necessary for our health, but the key is moderation. If the ratio of omega-6 to omega-3 compounds is too high in our diets, it can increase our risk of cardiovascular disease and other health issues (Simopoulos 2008).
Studies show that farmed salmon have far higher omega-6 to omega-3 ratios than wild-caught salmon (Strobel et al 2012). And our Western diets are already chock-full of omega-6s thanks to the large amounts of vegetable oils, especially soy oil, used in processed food (Simopoulos 2008).
Meanwhile, the level of omega-3s in farmed fish may be going down.
Omega-3 Levels Declining?
Most farmed fish are carnivores, like salmon, and so feeding them has traditionally relied on capturing vast numbers of smaller, wild fish like anchovies to use as food in captivity (Goldburg and Naylor 2005). But these feeder fish are declining fast, and it’s taking a toll on the fish farming industry. The BBC reported in 2016 that omega-3 concentrations in farmed salmon had fallen by about 50 percent in just five years due to the increasing use of alternative fish feed. And another study from 2016 found that using non-marine fish feed reduced the amount of the two important omega-3 fatty acids called EPA and DHA (Khan et al 2017). By 2015, as compared to 2006, a double portion of the fish was required to get the recommended amount of omega-3s.
Further research in mice backs up the harmful health effects of swapping out marine feed for vegetable oil in farmed fish. Mice fed salmon that had been raised on foods mixed with vegetable oil rather than fish oil had poorer metabolic health, greater insulin resistance and saw an increase in pro-inflammatory compounds in their bodies (Midtbø et al 2015).
It’s not just fatty acids, either. One study points out that wild salmon have four times more vitamin D than farmed salmon (Lu et al 2007). Vitamin D is something that our bodies need, but can’t always make. You might feel its absence most keenly in the winter, when a lack of sunlight means your body isn’t producing enough vitamin D. That can lead to a weakened immune system, and it’s a potential risk factor for poor mental health (Schwalfenberg 2010) (Humble 2010).
Why Salmon Are Pink -- Or Not
The crustaceans that salmon snack on in the wild also contain an antioxidant compound called astaxanthin. It gives salmon their characteristic pink color, and gives us another tool to fight off damaging free radicals in our bodies (Guerin et al 2003). As we’ve written before (Salmon’s Red-Orange Color Helps Hearts and Fights Belly Fat), farmers often give their salmon a synthetic version of astaxanthin that’s not as powerful as the real stuff. As a result, farmed fish often don’t contain the same dose of this potent antioxidant. In fact, most farmed salmon would be white, not pink, without the additives.
It can also be difficult for fish farmers to find the right nutritional balance. For example, it’s hard to know exactly how much selenium, an element critical for salmon growth and development, to put in fish feed. Either too much selenium or too little can be bad, and the wrong amount can impact the quality of the fish when we eat it (Khan et al 2017). What’s more, selenium is essential for human bodies as well, and fish can be a good source of the trace element. But, as one study points out, farmed fish typically have less selenium than wild fish (Vicente-Zurdo et al 2019). Farmed salmon also has smaller amounts of the minerals iron, zinc and potassium.
Ultimately, many of the reasons farmed salmon can’t compare to their wild brethren comes down to their diet. In attempts to cut costs and increase production, farmers often rely on feedstock that looks less like the food salmon normally eat and lacks some key compounds that make wild salmon so healthy for us.
Some issues in the fish farming industry are trending better in recent years, notably the reduced presence of harmful compounds like PCBs in farmed fish (Nøstbakken et al 2014). But farmed fish still aren’t as nutritious as wild fish. When it comes to providing a meal that’s natural and healthy, Mother Nature still knows best.
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