Improving the protein quality of New Zealand vegan diets: an optimisation modelling approach incorporating energy constraints and diet acceptability.

Introduction: Under consumption of certain indispensable amino acids (IAAs) is common in poorly planned vegan diets, but targeted dietary modifications through optimisation modelling can improve the overall protein adequacy and protein quality of these diets. Methods: Shortfalls in protein and IAAs in the existing diets of a sample of New Zealand vegans (stratified into three clusters with varying protein intake) were calculated by comparing daily intakes to individual requirements. An energy-tailored optimisation using linear programming was used to add protein-rich foods present in each individual's current diet to meet all protein and IAA requirements while respecting serving-size constraints and remaining within individual energy boundaries. When daily diets exceeded upper energy constraints, energy-dense and low-protein foods were identified and removed to accommodate the addition of protein-dense foods. Post-optimisation analysis assessed changes in intake of protein, IAAs, dietary fibre and selected micronutrients, with results compared across clusters. Results: Protein and IAA shortfalls were more prevalent in cluster 1 (85% of daily diets) compared to clusters 2 (61.1%) and 3 (30.8%). Legumes and pulses contributed most to total protein and lysine at lower energy costs, while nuts and seeds contributed most to methionine and leucine, but at higher energy costs. Optimisation resolved shortfalls using habitual diets in 90% of the daily diets. Post-optimisation micronutrient analysis showed continued risks of shortfalls for calcium, vitamin B12 and iodine. Discussion: Mathematical optimisation can enhance the protein adequacy and protein quality of vegan diets while preserving some individual acceptability. However, full adequacy remains challenging in energy-constrained diets with large deficits in protein and IAAs.