To our knowledge, this is the first study to simultaneously assess the nutritional quality and environmental impacts of self-selected diets in relation to levels of FV consumption. Diets were adjusted to 2000 kcal (theoretical average adult energy intake), which allows for standardisation and to have a homogeneous functional unit [39].

Our results revealed that the lowest consumers of FV (Q1) have an average intake of 119 g/d, which corresponds to less than 2 daily servings of FV. These low consumers are more likely to be young and to have a lower socio-economic level than the highest-level consumers. The most recent National Diet and Nutrition Survey in the United Kingdom (NDNS, 2020) showed comparable results, with 67% of adults surveyed reporting consumption of less than the quantities recommended in guidelines [40]. These observations are consistent with the situation observed in 2019 in Europe, with 88% of the population aged 15 years and over not meeting the recommendation [41].

We observed that nutritional quality increased systematically with increasing intakes of FV. Hence, high FV intakes were characterised by lower energy density and higher densities of vitamins C (126.6% in Q5 vs 42.5% in Q1), B9 (109.4% in Q5 vs 72.0% in Q1), potassium (97.4% in Q5 vs 76.6% in Q1) and fibre (78.5% of DRVs in Q5 vs 52.0% of DRVs in Q1), contributing to a higher MAR, and lower amounts of free sugars compared to groups consuming less FV. This finding is supported by data from the literature showing that FV contains high amounts of a wide range of beneficial nutrients including fibre, vitamins (A, B9 and C), and minerals such as potassium [42, 43]. In addition, higher consumption of FV was associated, in our study, with higher densities of nutrients that are not found in FV, such as nutrients that are specific to fish products (iodine and EPA + DHA) and to dairies (calcium), without reducing densities of nutrients specific to meat products (iron, vitamin B12), showing that an increased consumption of FV is associated with a more balanced diet.

Our results also showed that as FV consumption increased, MER decreased, showing the importance of increasing FV intake. However, this raises the question of substitution when increasing intake. According to our findings, the contribution of cereals and meat/fish/eggs remained similar in the different quintiles, which could allow us to suggest that the FV pattern is independent of the meat/egg/fish and cereal patterns.

Although our results showed an association between higher FV consumption and higher fibre intake, ranging from 51.95% of DRVs for Q1 to 78.45% of DRVs for Q5, the recommended intakes were not met in adults as mean intakes remained below DRVs in all quintiles. A review conducted in 2017 reported comparable results for adults in Europe, showing that fibre intake was below the recommendations. Grain products, especially bread, have been identified as the primary food source of fibre, while vegetables, potatoes and fruits are secondary fibre contributors, providing 12.0% to 21.0%, 6.0% to 19.0% and 8.0% to 23.0% of fibres, respectively [43].

Regarding the environmental impact of the studied diet, there were no significant differences in single EF scores between quintiles of FV consumption, showing that the level of FV consumption is independent of environmental impact when estimated with an aggregate indicator. This finding could be explained by the low contribution of FV to the single EF score, compared to other food groups. FV intake (excluding that from mixed dishes) contributed between 3% (Q1) to 14.6% (Q5) of the total single EF score, whereas the major contributors were meat products with 35.4% (Q3) to 40.7% (Q1) of the total. This finding is confirmed by EAT-Lancet [14] and World Wildlife Fund [44] studies, according to which meat and dairy food groups are the highest contributors to single EF scores, but also to other environmental impacts such as climate change, ozone depletion or fine particulate matter.

When the environmental indicators were analysed separately, higher FV consumption was associated with higher impact on water use compared to other food groups, but had less impact on climate change, fine particulate matter and ozone depletion, even for the highest consumers of FV (Q5). The low contribution of FV to the total impact (single EF score) compared to other food groups, and the characteristics of the French market (half of FV are produced in France, with a low amount of inputs and fertilisation in production) [45, 46] could explain their low impact on climate change, fine particulate matter and ozone depletion. Our results suggest that increasing the intake of FV at constant energy intake will have little impact on climate change, fine particulate matter and ozone depletion, but may increase water use impact. The contribution of FV should, therefore, be considered for reducing water use, although meat consumption remains the priority to reduce the environmental impacts of diet [16, 47].

A recent study assessed the environmental impact of diets in Sweden for six indicators (GHGE, cropland use, nitrogen (N) and phosphorus (P) application, consumptive water use and extinction rate). In this study, animal-based foods contributed most to the total environmental impact of diet (23.0–83.0%), followed by plant-based foods (8.0–40.0%), and discretionary foods (9.0–37.0%) for all environmental indicators. While animal-based foods contributed mainly to GHGE, cropland use, and N and P application, plant-based and discretionary foods had more significant impacts on consumptive water use and extinction rates (together responsible for 70–77% of the total dietary impact on these indicators) [48]. Comparable results were also observed in a recent population-based study conducted in Israel, where meat was the major contributor to land use, dairy to GHGE, and fruits followed by vegetables to water use; however, the authors highlighted that most FV in this country are grown using treated wastewater, which could reduce pressure on the environment [49].

The main strength of the present study was the matching of Agribalyse, the official national database on environmental impacts, with the INCA3 database, representative of all individuals residing in metropolitan France (excluding Corsica) and living in an ordinary household. In addition, INCA3 respects the methodology recommended by the European Food Safety Authority (EFSA) [50]. However, the INCA3 study, like all studies assessing dietary intakes, is based primarily on self-reporting by participants, which makes the reliability of the data partly dependent on the cognitive abilities of the participants, and on possible biases in reporting. Another limitation is the uncertainty in extrapolating long-term consumption from short-term cross-sectional, dietary reports [51]. Also, food consumption data from INCA3 were last updated in 2014–2015, whereas the food consumption habits of the French population may have changed since then, specifically due to the COVID-19 pandemic and inflation [52,53,54,55,56,57,58].

Our study also has several limitations and challenges that need to be addressed. It was impossible to dissociate the impacts of the ingredients of mixed dishes. Recipes indicating the amounts of ingredients for each meal enabled us to quantify the total amounts of FV for each individual. However, nutritional composition or environmental impacts were only available for the final dish and not for each ingredient, which made it impossible to assess the nutritional intake or environmental impacts of total FV consumption (i.e., including FV from mixed dishes).

Assessing the environmental performance of diets requires a multicriteria environmental perspective, going beyond climate change impacts alone [59]. In addition, optimal diets remain complex to model due to the many types of food products consumed, and the diversity of agricultural production systems, supply chains and local environmental settings. The majority of LCA databases are not exhaustive and lack data regarding the diversity of productions [59, 60]. Environmental data on FV production and imports from Agribalyse are generic estimates as not all crops are assessed [61, 62], which could impair the robustness of our results. However, LCA data were used for comparative purposes here and for the 2-by-2 comparisons, thus reducing the risk of over-interpretating absolute values that may suffer of uncertainties.

In addition, our results showed that not all environmental indicators behave similarly, confirming that it is essential to adopt a multicriteria assessment approach to better understand the environmental impact of diet.

Regarding the water use indicator, it would be necessary to approach this indicator more precisely, particularly by better taking into account spatial and temporal variability in LCA inventories and impact calculations [63]. Nevertheless, the results obtained on the overall dietary contribution to environmental impacts illustrate the importance of focusing on water use when adopting a more plant-based diet. This indicator has rarely been addressed, with scientific studies mainly focusing on GHGE and land use [16]. Linking the real contribution of adopting a more plant-based diet to water use is a short-term challenge, as global warming will make access to water resources more difficult and may potentially decrease FV consumption and thus disrupt the human health benefit/planetary health risk balance of FV. Production modes with irrigation techniques and territorial management should also be considered in the evaluation of water use, in order to identify pathways to reduce use of this resource. In fact, the efficiency of crop water use could be increased through irrigation strategies based on physical models of evaporation from partially wetted soil surfaces, irrigation water redistribution in the soil, and root water uptake. Micro-sprinkling seems to be the most suitable irrigation technique for efficient use of water, as it combines the advantages of drip irrigation with the capacities of sprinkler irrigation [64]. Other farm management practices will also play a key role in efficient water use, such as understanding soil types and structures, the need for water depending on the season and the development cycle of crops, keeping the soil covered with living or organic mulch to retain moisture, and selecting drought-tolerant crop species and varieties [65].