Commentary: Why diets need to change to avert harm from global warming

Extract

In this issue, Edwards and Roberts identify a connection between dietary affluence and impending harm from climate change¹ that has so far attracted little notice.² Fat populations, they argue, need more food (mainly to support their extra lean mass), and so amplify the greenhouse gas (GHG) emissions from food production. Fat bodies also need more fossil fuel to carry them around in cars and planes.

To elaborate their argument, they construct two hypothetical middle-aged populations of 1 billion with equal numbers of males and females. Male heights are set at 1.75 m and female heights at 1.60 m. One population is assigned a ‘normal’ body mass index (BMI) distribution with a mean of 24.5, with only 3.5% > 30.0—which is claimed to correspond to the UK in the 1970s. The ‘overweight’ population is given a BMI distribution ‘predicted for the UK in 2010’, with a mean of 29.0, and 40% >30.0 (obese). The authors estimate that the ‘overweight’ population would eat 19% more food, on the fragile assumption that their daily activity patterns were the same as the ‘normals’. Assuming further that the hypothetical 1 billion middle-aged ‘normals’ are equivalent to an average one-sixth of the total human population in their GHG emissions, the extra food needs of the ‘overweights’ would add 0.27 GT of CO₂ equivalents (CO_2e) to food-based emissions per year. To this, is added an extra 0.19 GT to transport the additional adipose tissue. The ‘overweight’ population is, however, more likely to be representative of heavy GHG emitters in high-income countries than of humanity in general. Allowing for this would push absolute emission increases upward. The authors conclude that the difference in emissions between the normal and overweight billions are likely to lie between 0.4 and 1.0 GT/year—equivalent, very roughly, to between 1 and 2% of the recent emissions from the total human population.