Meat, farmed catfish have highest environmental impact: Study

Industrial beef production and farmed catfish are the most taxing on the environment, while small wild-caught fish and molluscs, including oysters and mussels, have the lowest environmental impact, according to a study.

When compared to studies of vegetarian and vegan diets, a selective diet of aquaculture and wild capture fisheries has a lower environmental impact than either of the plant-based diets, researchers said.

The study, published in the journal Frontiers in Ecology and the Environment, is the most comprehensive look at the environmental impacts of different types of animal protein production.

"If you are an environmentalist, what you eat makes a difference. We found there are obvious good choices, and really obvious bad choices," said Ray Hilborn, a professor at the University of Washington in the US.

The study is based on nearly a decade of analysis, in which the researchers reviewed hundreds of published life-cycle assessments for various types of animal protein production.

As decisions are made about how food production expands through agricultural policies, trade agreements and environmental regulations, they note a "pressing need" for systematic comparisons of environmental costs across animal food types.

"Policymakers need to be able to say, 'There are certain food production types we need to encourage, and others we should discourage'," Hilborn said.

The researchers compared environmental impacts across food types by using a standard amount of 40 grammes of protein - roughly the size of an average hamburger patty, and the daily recommended protein serving.

Catfish aquaculture and beef produce about 20 times more greenhouse gases than farmed molluscs, small capture fisheries, farmed salmon and chicken, the researchers found.

Mollusc aquaculture - such as oysters, mussels and scallops -actually absorb excess nutrients that are harmful to ecosystems, they said.

In contrast, livestock beef production rated poorly in this measure, and capture fisheries consistently scored better than aquaculture and livestock because no fertiliser is used.

Farmed molluscs performed the best, with small capture fisheries and salmon aquaculture close behind, researchers said.