Fishing for a Better Diet

Stopping to Think More About Our Food From the Sea

Common pandora (seabream) with orange and fresh herbs
piazzagabriella / Getty Images

Fish has long been a mainstay in my Mediterranean diet. We still eat fish in the Katz household, but far less often and much more carefully than formerly.

This is not because I have changed my mind about the health benefits of eating fish for people. Rather, it’s because I have ever more concerns about the adverse health effects for the fish. Specifically, the growing, global human population is depleting the world’s fisheries and doing to the oceans just what we have done to the land. Our appetites for various animals as food have ramifications far beyond our own nutrition, spanning ethics, ecosystems, biodiversity, environmental disruption, and the climate.

It is, admittedly, inconvenient to have to consider all that at chow time, but we are all obligated to deal realistically with the times in which we live. This is our time, and such is the reality.

The Good and the Bad of Eating Fish

Fish is clearly good for us. Epidemiologic research—studies looking at health outcomes in groups of people—has long and consistently indicated better overall outcomes for people who eat fish routinely.

There are several potential reasons for this. One is that fatty fish and seafood provide concentrated doses of long-chain omega-3 fatty acids that are essential to our metabolism and hard to obtain anywhere else. Our Stone Age ancestors likely got some of the higher doses of omega-3 to which we are adapted from land animals that fed on wild plants. A theory gaining prominence in paleoanthropology, however, is that humans evolved preferentially at the interface of land and water, and that we have long been obtaining omega-3 fats from seafood.

Still, there are valid concerns about contaminants in fish. These include industrial chemicals, like PCBs, and heavy metals. Heavy metals, such as mercury, are subject to “bio-concentration,” meaning they accumulate up the food chain as larger animals eat smaller ones. Mercury is, thus, a particular concern in large, predatory fish, including swordfish and the bigger varieties of tuna. 

The research showing health benefits from eating fish is despite the presence of such contaminants, meaning that the benefits outweigh the harms. That said, there is a general advantage to eating medium-size rather than very large fish to avoid higher exposures to contaminants, with special attention to limiting potential exposure to mercury during pregnancy.

Fish Instead of What?

A key consideration related to the health effects of eating not just fish but any food that is often overlooked is what is eliminated from one’s diet to make room for it. Another reason for the health benefits of fish, beyond the omega-3s, is that fish in the diet generally displaces foods that are less good for us. People who eat more fish are prone to eat less red and/or processed meat. The benefits of eating fish routinely may derive in part from displacing meat and reducing saturated fat intake.

But the “instead of what?” question cuts both ways.  What about adding fish to a well-balanced vegetarian or vegan diet? We have no studies yet to answer this question directly, but data from a 2010 study out of Harvard are informative, as shown in this table from the paper. The bars depict the relative risks for coronary heart disease associated with replacement of one major dietary protein source by another; bars to the right mean higher risk, bars to the left mean lower risk. Fish reduces risk when it replaces any other animal food. But when plant sources of protein, namely nuts and beans, replace fish, they reduce risk further.

What this means is that eating fish is clearly good in the context of the typical American diet, where it is apt to replace meat. There is no convincing case, however, for making an effort to add fish to an otherwise balanced vegetarian or vegan diet, and there are important environmental arguments against doing so. Since populations with well-balanced vegetarian and vegan diets are among the healthiest and longest-lived in the world, it seems likely that fish confers greatest benefit by displacing other animal foods.

Wild-Caught or Farmed?

For those who do eat fish, an important question is whether farmed is as nutritious as wild. The answer really depends on farming methods, just as it does with animals on land. We know, for instance, that grass-fed, pasture-raised beef is nutritionally superior to grain-fed beef. The same is true for fish; the nutrition is best when the fish eat their native diets. Fish farming can compromise the diets of fish in a way that reduces their omega-3 content. Fish farms can also concentrate water-borne toxins, so that these are found at higher doses in the flesh of farmed fish.

As fish farming methods improve and become more transparent to us, there is every reason to expect farmed fish that is as nutritious as wild, and more sustainable. For now, though, the safest bet is to favor wild fish when you can. 

Making Smart Choices

But as noted at the start, the most important concern for me is increasingly the issue of sustainability. It really doesn’t matter how “good for us” wild salmon or swordfish is when we have eaten the world’s last one. Let’s be sure not to do that. 

Here, then, are my tips for anyone fishing for the best possible diet:

1) In the context of a standard American diet, eating fish will almost certainly improve your diet, and your health.  The best choice for nutrition is fatty fish, such as salmon.

2) For the time being, I would recommend wild fish over farmed, although farmed fish is still generally preferable to animal-foods farmed on land. So, feel free to swap out other meats for farmed fish, and be confident you are trading up.

3) Sustainability is a crucial consideration. The Environmental Working Group has a useful reference that can help you make smart choices at the market.

4) While we don’t know for sure if the “best” diet for humans includes or excludes fish, the research we have provides reason to favor plant foods even over fish. So, if you have a balanced vegetarian or vegan diet, you don’t need to add fish for the sake of your health; sticking with plants is, in fact, better for the environment. 

5) Omega-3 fats are essential. You can get plant omega-3s from walnuts and flaxseeds. The long-chain omega 3s found in fish can come from a supplement if you don’t eat fatty fish routinely. Good options include sustainably harvested krill, farmed mussels, or—best of all—algae.

We can all reel in better nutrition. Fish is optional.

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