Recently, Lawrence Reynolds of North Dakota State University published an editorial in The Journal of Nutrition in which attention was brought to the challenges associated with feeding the world’s rapidly expanding population. Reynolds writing was a response to a viewpoint put forth late last year by Donald Kennedy of Stanford University, who correctly pointed out that only through agricultural innovation and increased efficiency of food production can we hope to feed a population that is expected to reach nine billion by 2050.

What Kennedy failed to mention and what Reynolds seeks to remedy was the important role that animals play in achieving food security. Reynolds arguments boil down to four main points:

1. Animal products are an important source of high-quality, balanced, and highly bioavailable protein and numerous critical micronutrients.
2. Global demand for animal products is almost certain to continue to increase dramatically.
3. Farm animals are critical to a sustainable agricultural system, especially for small farms that comprise most of the world’s farmers.
4. Ruminants such as buffalo, cattle, goats, and sheep efficiently convert forages from grasslands into high-quality animal products, and grazing also promotes the health and biodiversity of grasslands if managed appropriately.

Although points #1 & 2 are unquestionable, points #3 & 4 have been debated for quite some time with regard to the impact animals have on the environment. Reynolds himself concluded that although animals will play an important role in feeding the world, a more complete understanding of their impact on the environment is necessary. I want to continue this discussion.

Leading the argument against animals, the United Nations Food and Agriculture Organization (FAO) wrote an assessment of the various significant impacts of the world’s livestock sector on the environment. Deliberately called Livestock’s Long Shadow, the assessment argues that there is a very substantial contribution of animal agriculture to climate change and air pollution, to land, soil, and water degradation, and to the reduction of biodiversity. However, not everyone shares this view. In response to the FAO assessment, researchers from the University of California published an article in which, using much of the FAO’s own data, they argue that the harms of animals are grossly overstated. I would go further and argue that the impact also depends on the type of animal production system and the method of data analysis.

Shortly after I had come across Reynolds editorial, a study out of Austria was published in Agricultural Systems where Paul Ertl et al. sought to calculate and compare the human-edible feed conversion efficiency (heFCE) of various livestock farming systems. After comparing six different farming methods across 31 Austrian dairy farms, Ertl et al. found that the composition of the cattle’s diet rather than the milk yield determines how efficient the dairy production system is. This is because the heFCE describes the relationship of human-edible output per human-edible input. As Ertl explains,

“From their nutritional ecology, cattle are specialists in digesting fibrous plant materials (e.g. forages) and do not necessarily rely on feeds that could potentially serve as human food (Gill, 2013 and Hofmann, 1989). However, due to enormous increases in animal performance during the last five decades, the inclusion of grains and pulses in cattle's diet has become necessary to meet the animals' nutrient and energy requirements (Knaus, 2013). As a result, in some cases beef and dairy production systems even show a heFCE below 1, indicating a net food drain (CAST – Council for Agricultural Science and Technology, 1999, Oltjen, Beckett, 1996 and Wilkinson, 2011).”

Thus there may be a huge misunderstanding in the animal farming system whereby the majority of research that is conducted in Western countries relies on concentrated animal feeding operations (CAFOs). Of course these animals show a drain on the environment and food security because they are eating a bunch of food that could be consumed by humans. Conversely, we can’t eat grass, and the outstanding role of grassland pastures for our food security future is indisputable. This topic is detailed nicely in a free full-text review by Frank Omara of The Irish Agriculture and Food Development Authority.

I want to turn attention towards data analysis now. In November of last year I wrote about a study conducted by Adam Drewnowski from the University of Washington in which the relation between the energy and nutrient content of foods and associated environmental cost (estimated by green-house gas emissions, GHGEs) was evaluated. Sure enough, on a per weight basis meat and dairy were the greatest sources of GHGEs. However, as soon as the plotting switched to a profile based on nutrient content instead of weight, meat not only performed the best but also showed a slight negative association with GHGEs whereby the more nutrient-dense the meat is, the less GHGEs it has. Conversely, there was a steep positive association for all other food categories such as grains and sweets, suggesting that the more nutrients you want from plants and snacks, the greater the GHGEs. This can be seen in the graphs below.