Environmental sustainability and nutritional quality of different diets considering nutritional adequacy

This study examines how four diets change nutritionally and environmentally when the diets are nutritionally adjusted. Data on individual Belgian diets of omnivores (n = 131), pescovegetarians (n = 159), vegetarians (n = 494), and vegans (n = 78) were obtained, called non-adjusted diets. We assessed if diets met energy and nutrient intake requirements and calculated the Alternative Healthy Eating Index (AHEI)-2010. The environmental impact was evaluated by a cradle-to-grave life cycle assessment considering all midpoint indicators of the Environmental Footprint 3.0 and expressing the impact per "daily food and supplement intake by one Belgian adult". The individual dietary intakes were adjusted nutritionally to meet the recommended energy and nutrition intakes using a quadratic programming algorithm. All diets had a significantly improved AHEI score but also a significantly increased water use (WU) when adjusting. The omnivore's diet demonstrated a significantly decreased carbon footprint (CF) while it significantly (except for vegans) raised for the restrictive diets due to adjustment. The omnivorous diet had the greatest improvements in AHEI (15.4), while WU increased the most among all diets (3.7 m³), primarily due to elevated fruit intake. The CF was reduced with 1.2 kg CO₂ due to decreased red meat consumption. The AHEI of the vegan diet improved the second most of all diets (13.2) due to the intake of omega-3 supplements, while its WU rose the least of all diets (2.4 m³), and its CF barely increased (0.1 kg CO₂-eq). The AHEI improvements of the vegetarian diet were similar to those of the vegan diet (12.5), while the one of the pescovegetarian diet was limited (3.5). The (pesco)vegetarian diet had an increase in WU (2.5 and 2.7 m³) and the highest increase in the CF (0.3 kg CO₂-eq). Since nutritionally adjusted diets do not lead to similar nutritional and environmental improvements, this research highlights the need to assess both metrics.