Studies such as the present on the assessment of food related environmental impacts of mean food dietary patterns, generally conclude that a shift towards less animal-based and more plant-based diets would have both a beneficial effect on climate and on the environment overall [3, 4, 24–29]. In the present study, it was found that the MDP implies lower demands on soil, compared to both the SCP and to WDP, and also on water and energy resources (even though our estimates were conservative). In fact, it was observed that a shift towards MDP would result in a reduction of the Spanish environmental footprint in any of the considered pressures from 33 to 72%. On the contrary, a progressive shift towards WDP would imply an increase in the footprints (12-72%). These results reinforce the sustainable character of the MDP in an increasingly globalised world [30, 31].
The comparison of the results on food environmental footprints between studies is complex because the results depend on a large variety of factors. A major limitation of this study was the use of data that has not been recently published, and the use of data from different countries (e.g. Northern Europe) belonging to different agro-ecological zones. However, despite some aforementioned limitations related to food intake and to environmental data sources used, the results in the present study are in line with most of the available literature [30, 31].
We consider our footprint estimates for land use and water consumption for the SCP to be realistic due to the agreement with the current real environmental pressures (Table 1). On the contrary, a slight overestimation of the energy consumption and GHG emissions footprints is acknowledged for the SCP. A comparison of the environmental footprints of the MDP and the WDP with the current real environmental pressures (rather than with the SCP) shows that the WDP would substantially increase all the environmental footprints. The adherence of the Spanish population to the MDP would decrease all the environmental pressures except energy consumption which would show an almost imperceptible increase.
As far as the environmental contribution of the different food groups is concerned, most of the literature available, despite originating from different settings and types of analysis, converges overall in the global statements. Plant-based foods were the group that contributed least to the selected environmental footprint, and as expected, in the MDP meat and dairy presented lower figures of water consumption and to a lesser extent energy consumption compared to the other patterns. Plant foods based on vegetables, cereals, and legumes are notably the food group with the lowest GHG emissions even where processing and substantial transportation is involved . In our study, legumes were included in the vegetable group as was indicated in other studies and since separate LCA data was not available. In fact, legumes are stated as alternatives to animal protein foods due to their low environmental impact and long durability . However, some vegetable origin foods contribute substantially, together with dairy products, in the case of the MDP and SCP, to either water consumption (vegetable oils in particular, and to some extent nuts) or land use (cereals and vegetable oils) in their production. In both the SCP and in the WDP, vegetal oils also contributed to a great extent to water consumption and to energy consumption footprints. Meanwhile animal-based foods were found to cause the highest environmental impact in all dietary patterns. As in other studies of the Spanish context, meat and dairy were the foods that most contributed to environmental footprints , although at a much lower absolute contribution than the WDP. As far as GHG emissions and land use were concerned, undoubtedly meat resulted as the food item that contributed most, showing a large difference compared to other foods, both in the WDP and SCP. It was observed that a reduction in meat consumption decreased GHG emissions , and land use, subsequently increasing the availability of land for other uses . Even though there is high production variability  which may be as much of 80% of global agriculture across countries, land use is related to livestock production and accounts for more than half of the GHG emissions resulting from agriculture . Meanwhile, dairy products, one of the main sources of animal protein in the MDP, contributed to a great extent in terms of energy consumption in the three dietary patterns. In the MDP, dairy products was the food group which presented the highest footprint in all 4 analyzed footprints since in the MDP meat has a lower weight compared to the other patterns both in frequency and amount (Additional file 3) . Regarding GHG emissions; fish also showed a remarkable environmental contribution in all the dietary patterns. According to our results, the MDP in Spain would substantially reduce overall water consumption: despite a possible increase in water consumption from vegetables and fruit groups. Water consumption of certain food groups as vegetable oils and fats or meat products would be lower than the WDP.
The most relevant dietary distinctions in terms of environmental cost were those that occurred between animal-based versus plant-based diets, with an important influence of the various ways foods are grown, processed, and transported. The largest environmental impact of food production from the farm level to consumers is generally associated with primary production. In terms of energy consumption, differences in greenhouse production versus open-air cultivation of certain crops, and canned or frozen-produce versus fresh-produce are substantial [25, 33]. Besides the energy involved in agricultural production, the amount of energy used in household food storage, preparation and waste is not negligible .
Food policy and dietary guidelines need to develop and move on from the classical approach which only focuses on nutrients and health, to one that takes into consideration environmental impact. Even consumers are tending to become more and more concerned about the environment and, even more so, about their personal health, there is a strong resistance to changing certain food choices (i.e. reducing meat consumption) whilst cultural culinary traditions are not easy to modify. Some studies state that even radical changes in food consumption patterns would provoke quite small environmental benefits [27–29]. A significant reduction in environmental footprints through a shift from the SCP towards a MDP type diet, would probably not only require substantial changes in consumers’ food choices but more specifically changes in agro-food-industry practices, public catering supply and agricultural and trade policies [7, 29, 34, 35]. Spain is one of the major producers and exporters of typical Mediterranean products, thus it would make sense to maintain a MDP agricultural production model.