Author Greenberg examines health, sustainability of seafood diet in recent HUCE event
By Alvin Powell, Harvard Staff Writer
Can we eat our way out of some global environmental problems?
That's a question asked by author Paul Greenberg, who has made his career writing about the problems of the seafood industry and seafood's potential — with careful management and a shift in consumer practices — to be the foundation of a healthier diet, promote more sustainable use of the environment, and even reduce carbon emissions.
Greenberg, the author of three books on fish, seafood, and the fishing industry, said one health benefit of eating more seafood is consuming more of the omega-3 fatty acids it contains. Those fats, also marketed commercially as supplements, have been long suspected to have heart-healthy effects, and results last fall from the VITAL study, led by JoAnn Manson, the Michael and Lee Bell Professor of Women's Health at Harvard Medical School and Brigham and Women's Hospital, showed that taking omega-3 supplements caused large reductions in cardiovascular risk for those who had little fish in their diet.
But "eating seafood" today means something different than it did just a few generations ago, Greenberg said. Instead of diets varying depending on locally available fish, recent decades have seen seafood becoming standardized, with the industrial focus narrowing to four foods: tuna, shrimp, salmon, and several species lumped together as "whitefish."
Those species can be very energy-intensive to harvest, and rediversifying the diet to increase the consumption of things like mussels and seaweed — which are both high in omega-3s and use much less energy to produce and process — can ease carbon emissions related to seafood harvesting.
Another strategy, Greenberg said, would be to utilize the 20 million to 30 million metric tons of smaller fish — currently ground up to use as fertilizer, for pig and chicken feed, and in aquaculture — for direct human consumption. That would increase the efficiency of a system that currently expends a lot of energy harvesting fish to feed them to something else that humans then eat.
With the planet's population slated to continue growing, future challenges include not just shifting toward healthier and less-energy-intensive diets, but also simply providing more food. Greenberg said the aquaculture industry has the potential to meet this need and could reduce current problems of near-shore pollution by co-locating its pens at offshore wind farms.
Greenberg, whose talk mirrored the title of his latest book, "The Omega Principle: Seafood and the Quest for Long Life and a Healthier Planet," spoke at Harvard's Science Center on Tuesday afternoon. His lecture was followed by a discussion with three Harvard nutrition and seafood experts, including Professor of Epidemiology and Nutrition Walter Willett, Assistant Professor of Nutrition and Planetary Health Christopher Golden, and Assistant Professor of Medicine Susan Korrick. The event was presented by the Harvard University Center for the Environment.
Their discussion, Willett said, goes to the heart of what will be one of the major challenges facing humanity over the next century: feeding a growing population in a sustainable way.
While omega-3 fatty acids are an important nutritional component of seafood, Willett said questions remain as to how much is needed for optimum health.
Studies have shown that omega-3 supplements can reduce cardiovascular risk among those whose diets contain little fish, he said, but it's likely that the effect plateaus and adding more beyond that to the diet would be of little use. At high enough doses, he said, some nutrients become toxic. Salt, for example, is an essential nutrient, but Willett said it's likely we've gone beyond the plateau of beneficial effects and typically eat too much.
"Like many nutrients, there's not a linear relationship between intake and how healthy we are," Willett said. "There are many things that are essential, but we don't need more."
Resource-poor parts of the world are facing a somewhat different scenario, Golden said. In places where locally caught fish provide important nutrients in the diet, fish populations are expected to shift and body sizes to decline due to climate change, portending difficult times. Fish provide not just calories and protein for more than a billion people, but also micronutrients that are absent from the tubers and grains that are likely to take their place in the diet.
"It's very troubling, in my opinion, to look at these types of statistics," Golden said.
In addition to nutrients, seafood also contains pollutants that concentrate as they make their way up the food chain, Korrick said. Those pollutants, such as mercury, have long been known to be a risk of marine foods, but the use of fish meal to feed land animals like pigs and chicken makes that a problem for the terrestrial food chain as well.
"If there's the political will and the political interest to really rethink and reimagine our food supply, considering contamination is a critical piece of that process," Korrick said.
Despite the many challenges, Greenberg contended that increasing seafood consumption, heightening use of aquaculture, and shifting toward less-energy-intensive foods point the way toward a sustainable future.
"We could end up with a planet that is more balanced and perhaps a human body that's more balanced," he concluded.