Are healthy dietary patterns aligned with sustainability?

Healthy lower impact diets can increase financial cost, despite the few scientific studies

Clarissa L.Leydon Centre for Health and Diet Research, School of Public Health, University College Cork, Ireland.

Most of the studies agree today to conclude that a healthier diet can align with sustainability, while reducing environmental impact. Nevertheless, focusing only on one environmental indicator such as greenhouses gas emissions can lead to a bias in sustainability and the choice of indicators may orientate the conclusions. A recent review reported that higher quality diet reduced planetary pressures whereas diets with lower environmental impact are not inherently optimal. Identifying higher quality diets that align with reductions across multiple environmental impact indicators may be challenging. Healthier, lower environmental impact diets can increase financial costs, and at the same time, be a “win-win” strategy against obesity and other non-communicable diseases.

For several years now, global organizations have been converging on the idea that it is possible to combine a diet that enables individual health with the health of the planet (EAT Lancet Food Planet), (Torsjen Ingird, 2019). The current recommendations are based on “a priori modelling”, not always realistic with the actual diet and sociocultural adaptation (Nicolas Bricas, 2011). On the economic dimension, studies show that healthy and sustainable diets remain unaffordable for many.

Illustrating the “a priori model” with actual diet in different countries remains essential to organize the transition. Therefore, a recent systematic review (Leydon et al., 2023) assessed the adherence to a priori defined dietary patterns based on 4 dimensions of a sustainable diet: diet quality, metabolic risk factors for NCD, environmental impacts, and affordability.

Healthier diets can reduce environmental impacts, but the reverse is not yet proven

According to this work, high nutritional quality diets reduce environmental pressure on the planet, although the reverse is not yet proven (diet with low environmental impact are not the best in terms of nutritional quality).

Areas of uncertainty need to be analyzed in terms of energy demand, greenhouse gases and water use, especially for vegetarian and vegan diets (Kesse-Guyot et al , 2020 ; Beiscrok et al, 2017 ; Rosi et al, 2017). Moreover, diets of high nutritional quality can have a positive effect on body mass index, although this is not systematic, whereas prospective studies confirm that adapted diets could combine the development of obesity with nutritional impact. This confirms the urgent need to organize dietary transitions in populations (Seconda et al, 2020).

Healthy lower impact diets can increase financial cost

The link between quality diet and cost has not been established, as the sample of studies that carried out this analysis was too small and was driven by a high consumption of organic produce. Only three studies reported higher financial cost associated with the adherence to food-based dietary guidelines (Kesse-Guyot et al., 2020; Baudry et al. 2019) and the EAT-Lancet diet (Kesse-Guyot et al., 2021) . Research suggests that healthy and sustainable diets (Drewnoski et al, 2020; Hirvonen et al, 2020) are less affordable, particularly in lower to middle-income countries, and those from lower SES groups.

In sum, reconciling the environment and nutrition is generally more expensive for consumers, even if this conclusion is moderate in developed countries, where the reduction in animal protein helps to contain the rise in the cost of sustainable food.

There is still room for improvement in cerain environmental areas, such as water management and affordability

In the context of climate change mitigation, a transition of food systems towards a sustainable development is essential to adapt to the consequences of climate change, preserve biodiversity, soil and water, protect the health of farmers and consumers, etc. However, this transition is complex to implement, particularly in view of the economic context of the actors in the food chain (Monsivais et al, 2015). Using the various methodologies recognized by the scientific community (measurements, models), we can identify areas for improvement to support the transition to sustainable diets, and then to investigate in systemic change.

The environmental impact indicator used for most studies is GHGE. Only one study covers water use and water toxicity, and only one covers a range of environmental impacts. The studies thus demonstrate a challenge for water use and affordability; yet they are too few to conclude. Making diagnosis of current systems as complete as possible remains one of the only ways of ensuring a rapid transition and improving measurement metrics. Including other indicators reflecting different dimensions of sustainable food systems should help to provide a holistic view to move toward more sustainable diet.

Based on : Leydon L. et al. Aligning Environmental Sustainability, Health Outcomes, and Affordability in Diet Quality: A Systematic Review. Adv Nutr. 2023 Nov;14(6):1270-1296.

Key messages
  • Costs of sustainable diets are still double challenge: evaluation and control.
  • Public policies should exploit the results of this systematic review in order to develop healthy and sustainable diets adapted to different populations
  • Too few studies have a holistic evaluation of diet (on a sustainable way): research on those fields remains expensive and some metrics and their area of uncertainties are still under process of evaluation for the scientific community.
  • Future works should consider other dimensions of sustainable food systems, such as affordability and water use.
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