A sustainable diet?

A recently published study by researchers at the Rowett Research Institute
in Scotland and part-funded by the UK branch of the World Wildlife Fund
provides an interesting comparison of what can be achieved by different,
nutritionally adequate diets, in terms of sustainability, in this case
measured by the reduction in greenhouse gas emissions (GHGE).

The ‘acceptable’ diet, based on foods consumed by at least half of the
UK population and including meat and dairy products, produced a 36%
reduction in GHGE compared with 1990 levels. However, the authors
acknowledged that after taking into account population growth, this
figure would be equivalent to reductions of just 30%, 25% and 14% at
2010, 2020 and 2050 population levels, respectively.

Comparing these figures with the target recommended by the UK Committee on
Climate Change to reduce UK GHGE from 1990 levels by 80% by 2050 (as quoted
in The Lancet 2009; 374: 2016-25) shows that the ‘acceptable’ diet does not
go anything like far enough.

In contrast, when the ‘acceptability’ constraints were removed, the
researchers’ model “generated a diet that met all energy and nutrient
requirements with a 90% reduction in the GHGE … but consisted of only
seven foods (whole-grain breakfast cereal, pasta, peas, fried onions,
brassicas, sesame seeds, and confectionery).” As the authors’ noted,
this essentially vegan diet “was unrealistic not only because of the
limited range of foods but also the inappropriate combinations of foods
(eg, a large quantity of breakfast cereal with no milk).” Presumably,
the addition of soy or other plant milk (“soya or mycroprotein products
as alternatives for animal-based products were not included because
they are not commonly consumed in the average UK diet”) and a greater
variety of plant foods could have produced a palatable, nutritious and
varied diet acceptable to vegetarians and vegans, if not to confirmed
meat-eaters, whilst still delivering a reduction in GHGE at least twice
as great as that of the ‘acceptable’ diet!

However, as the authors state, “with the use of the same methodology,
diets could be created to meet different dietary or cultural needs or
dietary preferences”, which sounds like a ‘come and get me’ to special
interest groups such as the Vegetarian and Vegan Societies in the UK!

Here is the abstract of the paper:

Sustainable diets for the future: can we contribute to reducing
greenhouse gas emissions by eating a healthy diet?

Jennie I Macdiarmid, Janet Kyle, Graham W Horgan, Jennifer Loe, Claire
Fyfe, Alexandra Johnstone, and Geraldine McNeill

ABSTRACT
Background: Food systems account for 18-20% of UK annual
greenhouse gas emissions (GHGEs). Recommendations for improving
food choices to reduce GHGEs must be balanced against dietary
requirements for health.
Objective: We assessed whether a reduction in GHGEs can be
achieved while meeting dietary requirements for health.
Design: A database was created that linked nutrient composition
and GHGE data for 82 food groups. Linear programming was used
iteratively to produce a diet that met the dietary requirements of an
adult woman (19-50 y old) while minimizing GHGEs. Acceptability
constraints were added to the model to include foods commonly
consumed in the United Kingdom in sensible quantities. A sample
menu was created to ensure that the quantities and types of food
generated from the model could be combined into a realistic 7-d
diet. Reductions in GHGEs of the diets were set against 1990 emission
values.
Results: The first model, without any acceptability constraints,
produced a 90% reduction in GHGEs but included only 7 food items,
all in unrealistic quantities. The addition of acceptability constraints
gave a more realistic diet with 52 foods but reduced GHGEs by
a lesser amount of 36%. This diet included meat products but in
smaller amounts than in the current diet. The retail cost of the
diet was comparable to the average UK expenditure on food.
Conclusion: A sustainable diet that meets dietary requirements for
health with lower GHGEs can be achieved without eliminating meat
or dairy products or increasing the cost to the consumer.

(Am J Clin Nutr doi: 10.3945/ajcn.112.038729.)

Paul Appleby

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