Modelling the nutritional impact towards more sustainable dietary protein intakes

Abstract

The current food system contributes substantially to deforestation, biodiversity loss, land use and global greenhouse gas emissions (GHGE), accounting for 20–35% of emissions. With the global population projected to reach 9.7 billion by 2050, a transition towards sustainable diets is necessary (FAO 2019). This thesis aimed to examine what constitutes a sustainable diet for the island of Ireland, informing sustainable dietary recommendations and providing a scientific basis for food-based dietary guidelines (FBDGs).

Linear programming (LP) was used to model sustainable diets using dietary data from the National Adult Nutrition Survey (NANS; Republic of Ireland) and National Diet and Nutrition Survey (NDNS; Northern Ireland cohort). Current nutrient and food group intakes, GHGE and blue water use (BWU) were assessed, with particular focus on protein and essential amino acid (EAA) requirements. LP scenarios incorporated constraints on nutrients, food groups, environmental impacts and protein quality.

Current diets exceeded the planetary boundary for GHGE, producing 4.8 kg CO2e/day compared with ≤1.87 kg CO2e/day, while remaining slightly below the planetary boundary for BWU, producing 732.7 l/day compared with boundary of ≤786 l/day. Protein and EAA intakes were adequate, but protein sources were predominantly animal-based, with meat and meat products contributing 40% of total protein energy. Sustainable diets meeting nutritional and protein quality requirements were achievable and featured increased plant-based foods and reduced animal-based and discretionary foods. Including additional food groups, particularly beans and pulses and nuts and seeds, substantially improved feasibility. Only 41% of individuals could achieve a sustainable diet without these food groups, compared with 99% when they were permitted. GHGE and BWU were reduced by 47% and 91%, respectively.

Diets exceed key environmental limits, particularly for GHGE. However, a more plant-forward dietary pattern, reduced discretionary food intake and greater dietary variety could enable nutritionally adequate and environmentally sustainable diets, providing a pathway for population-level dietary change.

References
Food and Agriculture Organization of the United Nations and World Health Organization (2019). Sustainable healthy diets - Guiding principles. Rome.

Thesis is embargoed until 31 December 2028.

Date of Award	Dec 2026
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Department of Agriculture, Environment and Rural Affairs & Department of Agriculture, Food & the Marine
Supervisor	Anne Nugent (Supervisor) & David Wright (Supervisor)