Sustainable food: weighed, measured, and found wanting?
An article by our Senior Expert for Nutrition Prof. em. Dr. Hannelore Daniel
The now almost inflationary use of sustainability as a normative term is on the one hand positive, because it creates awareness, but on the other hand the unreflective use and sometimes misuse of the term is also apparent. In many cases, the consumer is not informed of the basis for a product's sustainability claim. Furthermore, neither the list of criteria nor the rating scale of individual criteria of sustainability are defined in a binding manner and are, in any case, hardly comprehensible for non-experts. This makes product sustainability claims a matter of pure trust. And even then - as is usually the case - it is not as simple as one would like. Let's take the example of the food basket and the resulting climate-impacting emissions (Greenhouse gas emissions; GHGE).
What is the measure of all things?
Who defined that one must relate the evaluation criteria - such as GHGE - to the weight of the goods? Foodstuffs that contain a lot of water are thus usually those that have the lowest GHGE per unit of weight - let's take 100 g - even if they have a slightly higher impact during transport. A comprehensive analysis of about 480 food products conducted by a food retailer in France using LCA analyses as well as consumption data and product metrics from public databases concludes that in all food categories, fruits and vegetables - processed and/or frozen - have the lowest GHGE per 100 g, followed by confectionery, sweetened beverages, and sugar (1). Remarkably, as identified in other studies, household sugar has the lowest GHGE per 100 g of all foods. Of course, milk and dairy products have a much higher emission rate and meat or meat products lead to even higher rates. Here, however, the animal species must be taken into account. The list of meat species with the highest GHGE is topped by beef (there are still differences between dairy cow and male animal) followed by pork and poultry with the lowest rates.
All national recommendations on nutrition and food intake are based on the daily amount of energy requirement in kcal and the respective percentages of energy-providing nutrients (% of energy in the form of carbohydrates, protein, fat) rather than grams. Therefore, if we look at the above food groups based on their calorie content (per 100 kcal of ready-to-eat food), a rather surprising picture emerges. Now, all of a sudden, processed fruit and vegetable products (canned, convenience, frozen) are the ones with the highest GHGE, ranking ahead of meat and dairy products. In terms of calorie content, their emission rate increases by a factor of about 4, mainly due to transportation and storage. Confectionery continues to produce the lowest GHGE, in terms of energy as well as in terms of weight. Now, the FAO (Food and Agricultural Organization of the WHO) explicitly includes health and well-being as a criterion when classifying the "most sustainable diets". This then results in the low consumption quantity in the recommendations for confectionery. Thus, if the calorie contents are used as a reference basis, remarkable realities emerge for the dietary recommendations of all professional associations and the corresponding proportions of individual food groups in the shopping basket, which contrast with the public perception. This is currently characterized by the opinion that one only has to reduce or better stop the consumption of animal products to have the "most sustainable diet". However, this is only true if the replacement of animal products is not calorically compensated. If, on the other hand, the omitted calories are replaced isocalorically with processed fruit and vegetable products or plant-based substitutes, then either no net effect is achieved or even - depending on the degree of processing - a higher amount of GHG is emitted (2). While there are other good reasons to reduce the consumption of animal products (ethics and animal welfare, health), CO2 emissions are apparently not the measure of all things.
Everything in moderation
Based on consumption data from 1,918 consumers and the calculated GHGE of 73 of the most frequently consumed foods, there was a close correlation between the daily amount of calories consumed and CO2 emissions (2), which averaged 4,170 g CO2 equivalents per day across all consumers (with strong variance) (see figure). The diet in its entirety thus causes annual CO2 emissions equivalent to a flight (round trip in economy class) from Hamburg to Dubai. This does not provide an argument against changes in individual food consumption behavior; it is only intended to illustrate the dimensionality.
Unfortunately, even the consumption of regional products does not automatically lead to an improved balance in GHGE; certainly not if the purchase is done by car and involves driving further than 5 km (3, 4). Only if seasonal products are purchased preferentially, the CO2 burden can be significantly reduced.
From the data presented in the scientific studies cited here, it can thus be concluded that a higher sustainability of the diet - judged here on the basis of GHGE - can only be achieved with "moderation", i.e., a reduction in calorie intake. This is recommended anyway in view of increasing prevalence of obesity - a LESS is MORE approach should thus be included in the sustainability debate. One is inclined to give sufficiency the highest priority in all sustainability efforts.
- Drewnowski A. et al. (2015) Energy and nutrient density of foods in relation to their carbon footprint. Am J Clin Nutr 101:184-91.
- Vieux F. et al. (2012) Greenhouse gas emissions of self-selected individual diets in France: Changing the diet structure or consuming less? Ecological Economics 75, 91-101
- Edwards-Jones G. (2010) Does eating local food reduce the environmental impact of food production and enhance consumer health? Proc. Nutr. Soc. 69, 582-591
- http://www.ifeu.de/ fileadmin/uploads/landwirtschaft/pdf/IFEU_Umwelt_Regionale_Lebensmittel_2012_final_handout.pdf