Nutritional Quality of Diets
The nutritional quality of a diet, food or nutrient encompasses its benefits and detriments on the health of the consumer. The nutritional quality of the model diets with regards to the enlisted factors was assessed as described in section 2, and the results are presented herein. The nutritional quality of the diets consisted of their Food Compass and HENI scores and are plotted in Table 2. Both scores increased as the scenarios approached the optimal model diet. Food compass scores ranged from 65.46 (current diet) to 81.73 (optimal diet). Approximately 91.7% (22 out of the 24 diet scenarios) had FCS above 71, whereas the current diet (S1M1/M2/M3) and S2M2 (0.83% legumes, 1.39% processed meat, 4.89 red meat and 4% white meat) diet models recorded 65.46 and 70.90, respectively. According to the Food Compass Score categorization, consumption of foods with scores below or equal to 30 should be minimized, foods scoring between 31–69 are to be consumed moderately and above or equal to 70 are recommended. The Food Compass Scores exhibited approximately 93.3% positive correlation with the HENI scores, which ranged from 60.21 minutes per 100 kcal in the current diet (S1M1/M2/M3) to 320.85 minutes per 100 kcal in the optimal diet. Diet scenarios with lower calorie densities yielded higher HENI scores. This is evidenced in the 91.8% negative correlation between the calorie contents and HENI scores.
Table 2
HENI and Food Compass Scores of Model Diet Scenarios
Diet Scenario*** | Scaled FCS Score | HENI Score |
S1M1/M2/M3 | 65.46 | 60.21 |
S2M1 | 72.38 | 177.62 |
S2M2 | 70.90 | 177.01 |
S2M3 | 72.42 | 172.69 |
S3M1 | 72.48 | 176.45 |
S3M2 | 73.73 | 174.61 |
S3M3 | 72.81 | 172.55 |
S4M1 | 72.30 | 174.81 |
S4M2 | 73.08 | 173.52 |
S4M3 | 73.08 | 172.33 |
S5M1/M2/M3 | 71.79 | 168.06 |
S6M1 | 71.87 | 167.96 |
S6M2 | 73.38 | 169.84 |
S6M3 | 73.48 | 170.71 |
S7M1 | 73.77 | 181.73 |
S7M2 | 73.47 | 169.76 |
S7M3 | 73.44 | 170.50 |
S8M1 | 74.24 | 166.87 |
S8M2 | 73.46 | 169.65 |
S8M3 | 74.20 | 170.80 |
S9M1 | 73.16 | 171.55 |
S9M2 | 73.64 | 169.56 |
S9M3 | 74.13 | 169.21 |
S10M1/M2/M3 | 81.73 | 320.85 |
***See supplementary material (SD1-S3, SD1-S4, SD1-5, SD1-S6) for definition of summary definitions of diet scenarios |
Despite the strong positive correlation (93.3%) between the HENI and Food Compass scores, each nutritional assessment criterion yielded different rankings of the intermediate diet scenarios, including the default feasible diet on the Food4HealthyLife calculator. For instance, the S7M1 (6.89% legumes, 1.39% processed meat, 1.44% red meat and 3.47% white meat) diet model obtained a better rank (2nd ) under the HENI scoring system than under the Food Compass Scoring system, where it ranked 5th. In contrast, the S8M1 (7.56% legumes, 1.39% processed meat, 0.78% red meat and 3.47% white meat) diet model ranked better (2nd ) under the Food Compass system than under the HENI system, where it ranked 23rd. Despite the varying ranks, the current (S1M1/M2/M3) and optimal (S10/M1/M2/M3) diet models obtained the same ranking under both nutritional quality profiling criteria.
The trend of nutritional quality observed in this study is similar to the findings of Mozaffarian, et al. 43, who revealed that the Food Compass, NOVA, Health Star Rating and Nutri-Score nutrient profiling methods yielded dissimilar nutritional quality scores for American diets. Despite this conformity of our findings to previous studies 43, the Food Compass Scores were more sensitive to the compositional changes in our model diets compared to the HENI scoring system. In the Food Compass, diet scenarios between the current diet and existing model feasible diet obtained an average FCS of 71.86, lower than the average score of 73.52 for diet scenarios between the existing model feasible and optimal diets. Thus, diet scenarios with compositional quantities closer to the current diet generally ranked lower than scenarios with compositional quantities closer to the optimal diet scenario under the Food Compass system. The opposite was observed in the HENI score ranking, where diet scenarios between the current diet and feasible diet recorded a higher average score (174.62 min) than diet scenarios between the feasible and optimal diet (170.68 min) scenarios. The variation in scores for diet scenarios between the current and feasible diet scenarios [standard deviation = 2.36 (FCS); standard deviation = 36.22 (HENI)] was generally wider than the variation (standard deviation = 0.62 (FCS); standard deviation = 3.70 (HENI)] in the diet scenarios between the feasible and optimal diet scenarios. The variation in trend is attributable to the difference in considerations for the two scoring systems. We could argue that if the need for nutrition security is a global call, then the variation in diet quality assessment method is not a fair option. Most likely, a concerted methodology or metrics for quality assessment would ensure that a quality diet in one region corresponds to a quality diet in another region. However, it would be rather unfair to make this idea dominate the nutrition arena due to the current dynamics in nutritional burdens across the world that dictate what a quality diet would be for a sect of people within a specified timeframe. A single global methodology would therefore work in an ideal world of common nutritional distribution.
Domain Contributions (%) to Food Compass Scores
Out of the seven (7) domains used in the Food Compass nutrient profiling of the diet scenarios, six (6) contributed to the obtained FCS, as shown in Fig. 3. On average, vitamins contributed the most (31.41%), whereas specific lipids contributed the least (0.051%). The nutrient ratio (27.36%), minerals (10.99%), food ingredients (23.19%) and protein and fiber (6.99%) domains also demonstrated significant contributions. Generally, the contribution of nutrient ratios and food ingredients increased as the diet scenarios approached the optimal diet. In contrast, the contribution of minerals and vitamins decreased, while the contribution of protein and fiber varied minimally (mean: 6.99, standard deviation: 0.23) as diet scenarios approached optimal. Consequently, approximately 80% of the Food Compass Score of the current diet scenario (S1M1/M2/M3) was contributed by the mineral (40.15%) and vitamin (40.24%) domains. These were reduced to 24.18% and 14.11%, respectively, in the optimal diet scenario. The food ingredients domain constituted 41.18% of the optimal diet Food Compass Score while contributing only 4.18% in the current diet scenario. Within the intermediate diet scenarios, food ingredients contributed the smallest (19.89%) to the S2M3 diet scenario (1.11% legumes, 2.5% processed meat, 4.89% red meat, 4.0% white meat) and the largest (26.09%) to S9M3 (10% legumes, 0.28% processed meats, 0.11% red meat and 2.81% white meat). Mineral and vitamin domains also contributed from 25.41% in S9M3 and 28.54% in S9M3 (10% legumes, 0.28% processed meats, 0.11% red meat and 2.81% white meat) to 29.46% in S2M2 (0.83% legumes, 1.39% processed meat, 4.89% red meat and 4% white meat) and 33.75% in S2M1 (0.67% legumes, 1.39% processed meat, 4.89% red meat and 3.47% white meat), respectively. The largest contribution of the protein and fiber domain was 7.61% in the optimal diet scenario (S1M1/M2/M3), with the lowest contribution of 6.63% in diet scenario S9M3 (10% legumes, 0.28% processed meats, 0.11% red meat and 2.81% white meat).
Dietary Risk Components Contribution (%) to HENI Scores
Figure 4 presents the contribution of the dietary risk factors to the obtained HENI scores for the model diet scenarios. Vegetables, fruits, dairy, sugar-sweetened beverages, whole grains, seafood, beans/legumes, PUFAs, red meats and fiber are the main contributors to HENI scores; there were only minor contributions from sodium, calcium, TFA and nuts/seeds. On average, the greater contributors are vegetables (19.61%), fruits (18.09%), sugar-sweetened beverages (15.16%), milk/dairy (15.11%), whole grains (8.28%) and seafood (7.53%). The relative contributions of beans/legumes (5.59%), PUFAs (2.72%), red meats (2.74%), fiber (2.67%), processed meats (1.51%), seeds/nuts (0.75%), TFA (0.04%), calcium (0.16%) and sodium (0.04%) were also recorded. Hence, except for sugar-sweetened beverages, only minimal contributions were made from the harmful dietary risk factors, whereas beneficial dietary factors contributed largely. The percentage contribution increased from vegetables (15.75%), fruits (12.60%), seafood (3.15%), nuts/seeds (0%), beans/legumes (0%), fiber (1.98%) and whole grains (3.15%) to 22.83%, 22.83%, 11.42%, 1.43%, 11.42%, 3.22% and 12.84%, respectively, as the diet scenarios transitioned from the current diet to the optimal diet scenario. In contrast, the contribution decreased from sugar-sweetened beverages (31.50%), milk/dairy (18.90%), red meats (6.30%), processed meats (3.15%) and calcium (0.30%) to 0%, 11.42%, 0%, 0% and 0.04%, respectively. This trend of percentage contribution of the dietary risk factors to the HENI scores reflects the compositional substitutions applied during the modeling of the diet scenarios.
Environmental Impacts of Diets
In recent times, the environmental impact of diets has been as important to consider as their nutritional and human health impact. As presented in Fig. 5, the estimated environmental impacts for the diet scenarios indicate greater environmental impacts resulted from fossil energy use, freshwater ecotoxicity and ionizing radiation, which ranged from 0.64–1.28 MJ, 0.66–1.04 CTU eq and 0.79–2.19 Bq C-14 eq per 100 kcal, respectively. These are followed by global warming (short term) (0.08–0.20 kgCO2 eq/100 kcal), global warming long term (0.07–0.16 kgCO2 eq/100 kcal), land occupation (0.07–0.15 ha-yr/100 kcal) and total ecosystem quality damage (0.12–0.26 PDF.m2. yr/100kcal). The categories with the lowest impact were marine eutrophication, ozone layer depletion, photochemical oxidation, fine particulate matter formation, human toxicity (cancer and noncancer) and total human health damage. The diet scenarios also exhibited environmental impacts with regard to mineral resource use, freshwater acidification, terrestrial acidification, freshwater eutrophication, and water use.
Generally, the environmental impacts of the diet scenarios decreased as the scenarios approached the S9M3 (10% legumes, 0.28% processed meats, 0.11% red meat and 2.81% white meat) diet scenario and increased afterwards in the optimal diet scenario (see supplementary material, SD2 – S4). For instance, transitioning from the current model diet/S1M1M2M3 (0% legumes, 2.78% processed meat, 5.56% red meat and 4.17% white meat) to the S9M3 (10% legumes, 0.28% processed meats, 0.11% red meat and 2.81% white meat) diet model reduced global warming by 54.72%. The S2M2 (0.83% legumes, 1.39% processed meat, 4.89% red meat and 4% white meat) diet scenario recorded the highest impact for all environmental impact indicators except for freshwater eutrophication, ionizing radiation and fossil energy use. Similarly, the S2M1 (0.67% legumes, 1.39% processed meat, 4.89% red meat and 3.47% white meat) and S2M3 (1.11% legumes, 2.5% processed meat, 4.89% red meat and 4% white meat) diet scenarios yielded relatively higher impacts for all environmental impact indicators with the exceptions of ionizing radiation, freshwater eutrophication, and fossil energy use. An increase in global warming was observed in transitioning from the current diet scenario to the S2M1 (7.08%), S2M2 (7.59%) and S2M3 (7.56%) diet scenarios, where the authors propose a significantly increased intake of fruits, vegetables, whole grains, and fish in addition to the suggested changes in protein consumption (see Supplementary Material, SD1-S3, SD1-S4, SD1-S5). This observation signaled an increased intake of sustainable foods, while maintaining the consumption rates of unsustainable diets could potentially be environmentally harmful. However, maintaining the consumption rates of healthy and sustainable foods while significantly transitioning from 0% legumes, 2.78% processed meats, 5.56% red meat and 4.17% white meat (current diet/S1M1M2M3) to 10% legumes, 0.28% processed meats, 0.11% red meat and 2.81% white meat (S9M3) significantly reduced global warming by 54.72%. Hence, the S9M3 diet scenario emerged as the most environmentally friendly diet scenario. S9M2 (8.89% legumes, 0.56% processed meat, 0.78% red meat and 2.97% white meat) emerged as the second most environmentally friendly diet scenario for all indicators except ionizing radiation, freshwater eutrophication, and water use. For instance, it demonstrated a potential reduction in global warming by 46.22% relative to the current diet scenario.
The current diet scenario recorded the second highest impacts but only for global warming in the short term, land occupation, mineral resource use, terrestrial acidification, ozone layer depletion and fine particulate matter formation. It, however, produced the least impact on freshwater eutrophication. Additionally, the optimal diet scenario, which contained the highest quantities of whole grains, nuts, legumes, vegetables, fruits, and seafood with the lowest quantities of red meat, processed meat, white meat, eggs, refined grains, dairy and sugar-sweetened beverages, recorded the highest impacts on freshwater eutrophication and water use, the third highest impact on marine eutrophication and the fourth highest impact on photochemical oxidation. It generally produced impacts higher than the impacts from the S9M3 (10% legumes, 0.28% processed meats, 0.11% red meat and 2.81% white meat) diet scenario, which contained higher amounts of red meat, processed meat, white meat, egg, refined grains, dairy and sugar-sweetened beverages than the optimal diet/S10M1/M2/M3 (11.11% legumes, 0% processed meat, 0% red meat and 2.78% white meat) scenario (see Supplementary Material, SD1-S3, SD1-S4, SD1-S5).
The environmental impacts of all indicators except ozone layer depletion and ionizing radiation were lower in the current diet but increased in scenarios S2M1, S2M2 and S2M3, where the sum of quantities of whole grains, nuts, legumes, vegetables, fruits, and seafood began to increase, while the total sum of processed meat, red meat, white meat, dairy, eggs, refined grains, and sugar-sweetened beverages began to decrease. Buttressing this trend, the environmental impacts for diet scenarios between the current diet and the default feasible diet scenario/S5M1/M2/M3 (5.56% legumes, 1.39% processed meat, 2.78% red meat and 3.47% white meat) are higher compared to the impacts of diet scenarios between the default feasible and optimal diet scenarios for all environmental impact indicators. This trend is driven by the increasing partial replacement of the total sum of animal-based meats with legumes as the diet scenarios approached the optimal. This is due to the strong linkage of animal-based meats with greenhouse gas emissions 42,45,46 and, consequently, global warming. Global warming in turn correlates well with most environmental indicators. In this study, both short- and long-term global warming demonstrated strong positive correlations (correlation coefficient > 0.80 at α = 0.01) with all environmental impact indicators with some nuances for water use and freshwater eutrophication. This is similar to the findings of Stylianou, et al. 42. All other indicators apart from freshwater eutrophication and water use correlated similarly.
3.3 Nutrition-Environmental Trade-offs
Global warming exhibited a strong positive Pearson correlation (r2 > 0.80, α = 0.01) with all environmental impact indicators except water use and freshwater eutrophication. For this reason, the nutrition-environmental trade-off analysis was accomplished by utilizing each of the nutritional quality indicators with global warming in the short term, ionizing radiation and freshwater eutrophication. The results obtained are presented in Figs. 6 and 7. Comparing the food compass scores with global warming impact, ionizing radiation and freshwater eutrophication showed a decreasing environmental impact with an increasing food compass score. A similar observation resulted from trade-off analysis using the HENI scores. However, a nuanced trend occurred in the optimal diet scenario, where in all the trade-off analysis scenarios, both the nutritional quality scores and environmental impacts increased. The increased quantities of fruits, vegetables, cereals, legumes, and nuts in this diet scenario could account for this trend. Thus, although the quantities of red and processed meat in the optimal diet scenario were zero, the significant increase in the quantities of fruits, vegetables, cereals, and legumes could account for the increased diet quality and environmental impact. Therefore, the environmental impacts reached their lowest in diet scenario S9M3 while yielding corresponding high nutritional quality scores. Apart from trade-off analysis using the food compass score and global warming, where the S2M2 diet scenario was the least sustainable diet scenario, the S2M3 diet scenario was the least sustainable in all trade-off scenarios involving global warming and ionizing radiation. When freshwater eutrophication was included in the analysis (Fig. 7), the S2M2 diet scenario became the least sustainable diet using the Food Compass scores, whereas S2M3 became the least sustainable diet. The least sustainable diet scenarios are described as diet scenarios that had low nutritional quality scores and high environmental impacts. Consequently, the S9M3 diet scenario, which had approximately 76% of its total animal-based meats replaced with legumes, is the most sustainable diet scenario and qualifies as the optimal diet since it resulted in both high nutritional quality and an approximately 55% reduction in global warming, which correlates well with the majority of the environmental indicators.