How do we measure sustainable human nutrition?
Updated: Aug 14
Unless you've been living under a rock then you've heard the mantra that cattle are bad for the planet, right? This is a gross misconception, largely resulting from the ongoing mis-characterisation of the role of methane as a greenhouse gas.
Cattle are animals and not some sort of nefarious climate-heating machine. Ruminants have existed for millennia, while climate change is a more recent phenomenon. That said, some of the systems used to rear cattle are hugely problematic in terms of welfare and environmental impact. This potential paradox is summed up in the aphorism - 'it's the how, not the cow'.
I've written about the role of methane in global warming, and the broad misdirection of global averages, elsewhere on this blog.
Here I want to highlight Rothamsted research (Graham McAuliffe et al) that links nutritional value with global warming impact. (I also want to thank Julian Gairdner from Rezare Systems, NZ, for drawing my attention to it.)
While it's true that simple measures for global warming potential (GWP), such as CO2 equivalent/kg of meat, make beef and sheep farming systems look bad, this is because we not really asking the right question - or at least we're only asking part of a bigger question. The McAuliffe research changes the lens. It turns the traditional life-cycle assessment (LCA) model on its head and says, okay, so what happens if, rather than focussing on product weight, we look at nutritional value?
The research outlines a new LCA framework for livestock production systems that accounts for the nutritional quality of final products. This is important if we truly want to understand the value of a farming system to society. McAuliffe has used data from seven livestock production systems encompassing cattle, sheep, pigs, and poultry, and incorporated nutritional value of meat products into the livestock LCA. In doing this they dramatically alter our perception of the emissions intensity associated with different farm systems. When the nutrient content of meat replaces the mass of meat as the functional unit, cattle systems outperform pig and poultry systems in some cases.
To achieve this McAuliffe and his science team have used the recommended daily intake (RDI) nutritional requirements from the British Nutrition Foundation and mapped this across the nutritional content of different forms of meat and meat systems. Their nutrient index is based on 10 encouraged and two discouraged nutrients. In the graphs below you can see results which compare the traditional measure of CO2 equivalence/kg of meat with their new measure of CO2 equivalent/1% RDI. The transformation is remarkable.
Beef, which we know performs badly using the old metric, suddenly comes out best using the new metric. In other words, beef production in this analysis produces fewer kilograms of CO2 than any other meat, including chicken.
Okay,' I hear you say, 'I can see that cattle seem to be doing pretty well under this new metric, but what about lamb - that's still performing badly by comparison.' You're right - but another key factor is the land used to rear the animals. Sheep are generally reared on poorer quality land and their diets are not usually supplemented with much grain. When the science team factored in the arable land used to produce the grain to feed the livestock, lamb came out best, cattle did well - and of course chicken came out worst.
So - why am I highlighting this research? Well, to be honest it's partly because I'm fed up with being told that ruminants are bad, and that if I want to find a climate friendly meat then I need look no further than chicken. Instinctively I know this isn't true, but it's really helpful to have some science that starts to address some different questions in relation to meat production and global warming. CO2/kg is a blunt and simplistic metric - it doesn't, for example, factor in the differing behaviours of different greenhouse gases, and it doesn't consider nutrition. It certainly doesn't consider the wide variety of different farm systems used for producing cattle.
And to be clear - I'm not writing this because I think we should all be eating loads of meat. Globally our meat consumption must reduce significantly, but if our concern is global warming, then our decisions should be based on accurate science and a more holistic approach to understanding the costs and benefits of meat production.
The Rothamsted research provides yet another strong argument for grass-based ruminant systems on non-arable land.