Humans Share Food Chain Level With Pigs, Study Finds

Scientists calculate a trophic level for humans.

Apex Predator

An orca rams a young gray whale near Unimak Pass, Alaska. Orcas are carnivorous apex predators and hold the highest spot in their food chains. People's varied diets, on the other hand, give them a middle trophic level, in spite of their technology.Photo by John Durban, working with the NOAA Alaska Fisheries Science Center and the North Gulf Oceanic Society

Where do humans fall in the food chain? You can probably already guess it's somewhere between cows and polar bears, but a new study now puts a number to it: Somewhere between 2.0 and 2.6, depending on where you live. That's on a scale of 1 to about 5, in which plants are 1s and carnivorous apex predators like killer whales are 5.5s.

In other words, humans are in kind of the same plane as anchovies and pigs.

As people in developing countries eat more meat, their trophic levels rise.

The technical term for the number the researchers calculated is the "trophic level." A species' trophic level is based on the balance of meat and plants it consumes, and whether that meat comes from herbivores or animals higher up in the food chain. (Eating tuna gives you a bigger trophic level boost than eating sardines.) This is why people fall in the middle, although unlike pigs, they have the technology to take down animals in higher trophic levels, such as lions and tigers. Ecologists calculate species' trophic levels to help them get a handle on how energy and edibles move through different ecosystems.

No one has ever calculated a trophic level for humans, the research team wrote in a paper it published today in the Proceedings of the National Academy of Sciences. The team decided to do so to show that it could be useful as a way of comparing diets in different countries. It could also be an easy-to-understand shorthand for tracking food trends around the world. For example, as people in developing countries eat more and more meat, their trophic levels rise. In 1961, the median trophic level for people in China and India was 2.05. By 2009, those countries' median trophic level was 2.20.

Other interesting things the researchers found about people's trophic levels:

  • If researchers don't include India and China in their worldwide trophic level calculation, the average global human trophic level has actually stayed pretty steady around 2.3 over the past 50 years.
  • The trophic levels of the fish people eat has fallen, from 2.88 in 1961 to 2.69 in 2009. That's because fisheries around the world have been catching fewer big predator fish, in part because of overfishing.
  • The countries with the highest trophic levels in the world include Mongolia, Mauritania, Iceland and the Scandinavian nations, all of which have traditional diets based on meat, fish, or dairy, and few vegetables. However, their trophic levels have fallen since 1961. In Scandinavia, government agencies launched campaigns to get people to eat more veggies. Meanwhile, in Mongolia and Mauritania, people are eating less traditional diets now as a result of modernization and urbanization.