Which carb.?

I’m attempting to become a more ethical eater, in the hope that small / individual / bottom-up changes will inspire larger / collective / top-down ones.

It’s hard though. I have some food allergies, I’m a bit lazy, and there are just so many factors to consider. I want to simultaneously minimise the carbon and water footprint of the food I buy, whilst reducing animal suffering and supporting producers trying to make a fair living.

One variable I don’t hear much about is land footprint – what choices can I make to minimise the land required to produce the food I eat? If anything, this is the factor I care about most, because minimising cultivated land area should maximise natural habitat area, which in turn should conserve more carbon, water and wildlife.

With this in mind, I’ve attempted to work out the total area required to supply 65m Britons with their annual recommended intake of carbohydrates from different sources.

>>Carbohydrates (RDI = 260 g)

I’ve selected the three main sources of carbohydrate in my diet: pasta, long grain white rice and potatoes. I’ve assumed that: pasta (746.7 g/kg carbohydrate) is made from Italian Durum wheat, yielding 3.9 t/ha with a 70% milling ratio; rice (799.5 g/kg carbohydrate) is grown in the USA, yielding 8.5 t/ha with an 80% milling ratio; potatoes (174.9 g/kg carbohydrate) are grown in the UK, yielding 37.8 t/ha. These yield estimates are from the FAO, and I’ve pulled nutritional information from the USDA Food Composition Database.

Rice and pasta have similar carbohydrate contents, but rice yields are more than double Durum wheat yields; so rice wins. Potatoes are higher yielding still, so despite their lower carbohydrate content, they beat rice (at least in terms of land footprint – they require larger inputs of sprays, fertilisers and water compared to other crops).

fig1.png

The area of the circle is equivalent to the area required to provide 65m Britons with their annual recommended intake of carbohydrates from either pasta, potato or rice. (Sorry Eire)

Still, even if we were interested only in land footprint, we couldn’t derive all our carbs from potatoes – you can’t grow potatoes (or any crop, really) year in, year out in the same field. You need break crops, both in time and space. To illustrate the effect this has on yield, imagine that all potato fields need to be left fallow for a year to recover; the ‘annualised’ yield would then be halved. I don’t think I know how to properly account for this in my back-of-envelope calculations above.


Conclusion: It’s a bit complicated. I don’t imagine this exercise will change the way I shop, but I think the maps are effective. I don’t think carbohydrates are the frontier of ethical eating though. Need to repeat for protein.


>>Protein (RDI = 60 g)

Update! I found a review of the land-use intensity of protein from different sources (based on full life-cycle assessments rather than back of envelope calculations). As above, I’ve plotted the area required to provide 65m Britons with their annual recommended intake of protein. I’ve used the mid-point of the minimum and maximum estimates from Nijdam et al‘s (global) review.

 

fig2.png

The area of the circle is equivalent to the area required to provide 65m Britons with their annual recommended intake of protein (60 g per day) from different sources. Based on the mid-point of the minimum and maximum estimates of land-use intensity from Nijdam et al. 2012 Food Policy 37.

 

Caveat: In converting between kilos and tonnes and hectares and squares kilometres, I might have messed up by a few decimal places. This would be a great shame. But I think everything looks of the right order of magnitude?

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