A study of human trophic levels has shown China and India have driven a move towards eating more meat. But Australia and some other western countries have moved the other way

This article is more than 6 years old

This article is more than 6 years old

Humans are becoming more carnivorous worldwide, though Australia and some other western countries are eating less meat.

A new study has applied the ecological concept of trophic levels to humans, by analysing 49 years of food consumption data from the Food and Agriculture Organisation.

Trophic levels are a concept used to define species' roles in ecosystems. It assigns a rank to each species depending on the composition and trophic level of their diet. Plants have a trophic level of one. Herbivores, such as cows, have a trophic level of two. A species that has a diet composed of half plant and half animal would have a trophic level of 2.5. Apex predators can have trophic levels reaching up to 5.5.

Since 1960, the study shows our median human trophic level (HTL) has increased by 3% to 2.21 in 2009, meaning we are becoming more carnivorous on the whole, occupying a similar trophic level to that of pigs or anchovies. This increase over time is mainly driven by China and India, as the following graph shows:

World human trophic levels. Photograph: Bonhommeau et al 2013/PNAS

Country by country, you can see how trophic levels have changed with this animated map:

Click here for the map on mobile.

Sub-Saharan Africa and parts of south-east Asia have low and stable HTLs, indicating a more plant-based diet. Countries such as Iceland and Mongolia have the highest HTLs, and therefore a higher meat diet. Australia, New Zealand, North America, and parts of Europe had high HTLs that have recently begun to decrease since 1990, indicating a shift from a high-meat diet towards a more plant-based diet.

Here is how Australia's human trophic level looks over time:

Human trophic levels in Australia. Photograph: Bonhommeau et al 2013/PNAS

The authors attribute this recent decline to greater awareness of the health problems associated with high-fat and -meat diets, and subsequent government-run education programs to encourage a move to a more balanced diet.

Dr Ross Thompson, of the Institute for Applied Ecology at the University of Canberra, said applying the trophic level concept to humans was "entirely appropriate".

"The really unique thing is our ability to feed on many different levels," he said. "We can feed on high trophic level animals like sharks, but we can also feed on algae."

Thompson said the emergence of a higher meat diet overall was concerning. "For every trophic level we go up we lose about 90% of the energy, so you need an increase in the productive area. There's big inefficiencies as we move up food chains," he said.

The study also examined the correlation between the human trophic level and various World Bank development indicators. It found a significant correlation between HTL and things such as GDP, life expectancy, CO2 emissions and urbanisation.