Are Humans Becoming More Carnivorous?

Photo courtesy of Farming America

At the beginning of December, Nature News published an article titled Humans are becoming more carnivorous. The article discussed how global meat consumption has increased since the 1960s. The article describes the findings of a new study, Eating up the world's food web and the human trophic level published by Bonhommeau et al. (2013) in the peer-reviewed journal Proceedings of the National Academy of Sciences.

Bonhommeau et al. (2013) used the trophic level concept to quantify human diets. Trophic levels are often used to define the roles of species in ecosystems by describing the energy levels associated with primary producers, secondary producers, and tertiary producers (Kercher and Shugart, 1975). Species belonging to the lowest trophic levels are primary producers (e.g. algae, plants), and species belonging to the highest trophic levels are top predators. When moving from one trophic level to another, a loss in energy occurs (Kozlovsky, 1968). Bonhommeau et al. (2013) calculated the Human Trophic Level (HTL) for the very first time using human food supply per food item per capita per year national data from the Food and Agriculture Organisation (FAO). The data represent 98.1% of the world population between 1961 and 2009.

Their results indicate a 3% increase in HTL since 1961 (as shown in the figure below). By using a weighted average to represent different countries' populations, the researchers found that much of this increase was driven by China and India (HTL increase of 7.4%). 

A) Trends in the HTC (1961-2009) and B) Map of the median HTC level over 2005-2009 (Bonhommeau et al., 2013) 

Although there is a considerable amount of inter-country variability within the results, cluster analysis has shown that there are five different groups of HTLs:

The first group includes sub-Saharan countries and Southeast Asia and exhibits patterns of low and stable HTLs due to that fact that populations in these regions have mainly plant-based diets. The second group includes countries from Asia, Africa, South America, including China and India, and exhibits low but increasing HTLs. The third group includes Central America, Brazil, Chile, Southern Europe, several African countries, and Japan. It has higher HTLs than group 2 and exhibits an increasing trend. The fourth group includes North America, Northern and Eastern Europe, Australia, and New Zealand, and has high and stable HTLs until 1990 which increase thereafter. Finally, the fifth group possesses the highest overall HTLs and decreasing trends, and includes Iceland, Scandinavia, Mongolia, and Mauritania.

In addition to the trends described above, the results found by Bonhommeau et al. (2013) challenge the classic view of humans as top predators - based on their analysis, humans were placed on the same trophic level as anchoveta and pigs (level of 2.21). The researchers also found that the trophic level of terrestrial animals consumed by humans has only slightly increased, while the trophic level of marine food items has decreased due to declines in the mean trophic level of marine fisheries catches. 

When I first read the article in Nature News, I was a little bit surprised to learn that global meat consumption has increased despite so much recent emphasis on meat consumption reduction, for example through campaigns such as Meat Free Mondays. However, reading through the results, the numbers do add up. When looking at the bigger picture and taking into account the economies of different countries, we still see a growing preference for a western-style diet. 

What does a global increase in meat consumption imply? I'll be back to explore the potential environmental impacts in the next post.

Thanks for reading!