Introduction
Food production has become one of the most outstanding social, environmental, and economic challenges in current times (FAO, 2020). It is estimated that, with the current population growth rate, within 30 years, it will be necessary to increase global food production by 70% (United Nations, 2019). Consequently, animal source food would double by 2050 (Alexandratos and Bruisma, Reference Alexandratos and Bruisma2012), which will generate great environmental pressure (Ritchie and Roser, Reference Ritchie and Roser2020). Livestock production is one of the main contributors to land degradation (Van Kernebeek et al., Reference Van Kernebeek, Oosting, Van Ittersum, Bikker and De Boer2016), water consumption (Hoekstra, Reference Hoekstra2012), and greenhouse gas (GHG) emissions (Gerber et al., Reference Gerber, Steinfeld, Henderson, Mottet, Opio, Dijkman, Falcucci and Tempio2013). For this reason, there is a global trend to change dietary patterns and an increasing commitment to alternative protein sources (Fanzo, Reference Fanzo2019; Hu, Otis and McCarthy, Reference Hu, Otis and McCarthy2019; Weinrich, Reference Weinrich2019; Röös et al., Reference Röös, Carlsson, Ferawati, Hefni, Stephan, Tidåker and Witthöft2020; Andreoli et al., Reference Andreoli, Bagliani, Corsi and Frontuto2021; FAO, 2022). Nevertheless, meat is a great source of protein (WHO, 2018) and an economic livelihood for a large part of the world’s population (Keathley, Reference Keathley2021). Since the environmental impact of meat and crop production depends, to a great extent, on the production system used (Moran and Wall, Reference Moran and Wall2011; Van Zanten et al., Reference Van Zanten, Meerburg, Bikker, Herrero and De Boer2016; WHO, 2018; Peyraud and MacLeod, Reference Peyraud and MacLeod2020), not all meat products should be considered as unsustainable choices. Therefore, and to evaluate the sustainability of the different meat and plant-based products, sustainability indicators can be used as a reference of their environmental performance (Jones et al., Reference Jones, Hoey, Blesh, Miller, Green and Shapiro2016; Aldaya et al., Reference Aldaya, Ibañez, Domínguez-Lacueva, Murillo-Arbizu, Rubio-Varas, Soret and Beriain2021).
In order to assess the environmental performance of a hybrid burger and its plant- and animal-based alternatives, two sustainability indicators have been used: the water footprint (WF) and the carbon footprint (CF). The WF measures the amount of water used to produce a good or a service (Hoekstra et al., Reference Hoekstra, Chapagain, Aldaya and Mekonnen2011), whereas the CF measures the sum of GHG emissions and GHG removals in a product system, expressed as CO2 equivalents (CO2e) (ISO/TC 207/SC 7, 2018). In this study, we focused on WF and CF since they are widely recognized as key indicators for assessing the environmental impact of food production, particularly in terms of resource use and climate change. Other environmental impact categories, such as land use, eutrophication potential, and biodiversity loss, are also relevant in food production but were excluded in this study for several reasons. First, several studies (Mekonnen and Hoekstra, Reference Mekonnen and Hoekstra2010; Poore and Nemecek, Reference Poore and Nemecek2018) highlight WF and CF as the primary environmental pressures in food products like burgers. Second, these indicators are also robust, quantifiable metrics commonly used in environmental life cycle assessments (LCAs), allowing for more robust comparisons. Moreover, other studies such as those by Clune, Crossin and Verghese (Reference Clune, Crossin and Verghese2017) and Smetana et al. (Reference Smetana, Mathys, Knoch and Heinz2015) have conducted LCAs of burgers, focusing primarily on WF and CF, which further supports their relevance as key environmental indicators for this study.
Even if there are several publications that have already evaluated the WF and CF of meat and/or plant-based burger patties (Fiala, Reference Fiala2009; Peters et al., Reference Peters, Rowley, Wiedemann, Tucker, Short and Schulz2010; Ercin, Martinez-Aldaya and Ysbert Hoekstra, Reference Ercin, Martinez-Aldaya and Ysbert Hoekstra2011; Hoekstra, Reference Hoekstra2012; Smetana et al., Reference Smetana, Mathys, Knoch and Heinz2015; Chaudhary and Tremorin, Reference Chaudhary and Tremorin2020; Arrieta et al., Reference Arrieta, Aguiar, González Fisher, Cuchietti, Cabrol, González and Jobbágy2022), there remains a significant gap in the literature regarding the environmental assessment of hybrid burgers. There are several studies where alternative protein sources, such as soya, peas, pumpkin, or insect flours, have been evaluated (Keoleian and Heller, Reference Keoleian and Heller2018; Saerens et al., Reference Saerens, Smetana, Van Campenhout, Lammers and Heinz2021; Saget et al., Reference Saget, Porto Costa, Santos, Vasconcelos, Styles and Williams2021; Smetana et al., Reference Smetana, Profeta, Voigt, Kircher and Heinz2021). However, most existing studies have analyzed meat-based and plant-based patties separately, without considering the environmental trade-offs associated with their combination in a single product. Hybrid burgers, combining plant-based and meat ingredients, offer a balanced approach by enhancing nutritional value, improving sensory quality, and introducing a novel, more sustainable alternative to traditional beef burgers.
Moreover, our study stands out by evaluating the nutritional productivity of the burgers in terms of both carbon and water use, a measure that reflects the amount of nutritional value produced per unit of environmental impact. This concept is particularly relevant in the context of plant-based diets, which have been associated with multiple health benefits, including lower risks of cardiovascular disease, obesity, and type 2 diabetes, as highlighted by Satija et al. (Reference Satija, Bhupathiraju, Rimm, Spiegelman, Chiuve, Borgi, Willett, Manson, Sun and Hu2016) and Willett et al. (Reference Willett, Rockström, Loken, Springmann, Lang, Vermeulen, Garnett, Tilman, DeClerck, Wood, Jonell, Clark, Gordon, Fanzo, Hawkes, Zurayk, Rivera, De Vries, Majele Sibanda and Murray2019). While fully plant-based diets offer these advantages, they sometimes lack key nutrients, such as vitamin B12, heme iron, and high-quality protein, which hybrid burgers can help provide by incorporating animal-derived components. This approach, which combines environmental and nutritional performance, is distinct in the literature. Nutritional productivity has been explored in previous studies, such as those by Hoekstra (Reference Hoekstra2012) and Springmann et al. (Reference Springmann, Wiebe, Mason-D’Croz, Sulser, Rayner and Scarborough2018), who assessed the environmental efficiency of food products by considering not only resource use but also their nutritional contribution. Blending the high nutritional value of beef protein with the lower environmental footprint of plant-based ingredients, our research offers a more comprehensive understanding of sustainability. This perspective is crucial when considering productivity relative to water and carbon, as it enables a more holistic assessment of the trade-offs between nutritional quality and environmental impact. This comparison is particularly significant as it provides a balanced solution to the environmental challenges posed by fully animal-based diets, bridging the gap between conventional and plant-based options, and addressing key sustainability indicators often overlooked in other studies.
This study focuses on the environmental impact of a hybrid burger that combines beef with plant-based proteins from soybean, rice, and beans, an alternative not extensively explored in the literature. While previous research (Shahid et al., Reference Shahid, Shah, Mach, Rodgers-Hunt, Finnigan, Frost, Neal and Hadjikakou2024) has compared alternative protein sources (like mycoproteins) from a life cycle perspective, hybrid options have not been the primary focus. The study by Chaudhary and Tremorin (Reference Chaudhary and Tremorin2020) directly evaluated the nutritional and environmental sustainability of a hybrid burger made with lentils and beef. By examining this hybrid burger option, our research offers a novel contribution that not only provides insights into a potential middle ground between animal and plant-based burgers but also highlights its nutritional and environmental benefits.
Materials and methods
System boundaries and burgers under study
The main goal of this research is to calculate the amount of freshwater (WF) and GHG emissions (CF) associated with the production of three 150 g burgers of different origins (beef meat, plant-based, and hybrid) in order to assess their nutrition and environmental performance before reaching consumers. In order to estimate the WF and CF of the three burgers under study, we considered different upstream and core processes along the supply chain (see Fig. 1). Downstream processes take place after a product or service leaves the company’s control and/or ownership. For this reason, and due to the uncertainty they generate, they are considered to be outside both the objective and the scope of this study.
Figure 1. Flowchart of the supply chain used for the calculation of water footprint and carbon footprint of the three burgers under study.
The aspects considered for the calculation of the WF and the CF were similar among the supply chain of the three burgers. On the one hand, for the calculation of the WF and CF of the meat burger, we considered two stages that are only included in the supply chain of the meat and hybrid burgers: the animal production and growth, and slaughterhouses stages. On the other hand, the plant-based burger and the hybrid burgers have other two stages that are not taken into account for the meat burger: the crop production and the protein preparation stages. The final cooking or burger-making stage, corresponding to the core processes, is common to the three of them. The study focuses on a pilot-scale production system.
Animal production and growth
The meat is produced in the northern part of Navarra, and it is sealed with the Protected Geographic Indication (PGI) Ternera de Navarra hallmark. This means that the production system applied is mixed; it combines grazing and milk fed along the first 4 months with fattened feed from 5 to 11 months (Table 1). Within the animal production and growth stage, the enteric fermentation refers to the methane (CH4) emissions produced by the food digestion of cattle.
Table 1. Summary of some of the characteristics that the Protected Geographic Indication (PGI) Ternera de Navarra’s beef must have to comply with the current legislation that also contribute to the sustainability of its production
Slaughterhouse
The slaughterhouse activities have minimal water consumption, and the main environmental impact is derived from the energy consumption of machinery. The activities at the slaughterhouse use, on average, 500–1,000 liters per animal (AINIA, 2020). However, most of the water used is treated and immediately returned to the same basin. Moreover, according to the Köppen climate classification (Kottek et al., Reference Kottek, Grieser, Beck, Rudolf and Rubel2006), Navarra is a region with abundant rainfall throughout the year and does not have a dry season. In that way, the WF was assumed to be negligible at that stage.
Crop production
The beans and rice used to produce the plant-based protein are grown in Spain, whereas the soya comes from the United States. Since no specific data on the production system or exact location of these crops were available, we used average country data from databases, which represent the mean values across all production regions within each country for CF and WF calculations.
Protein preparation
The plant-based protein used in the plant-based and hybrid burgers is produced at the factory of Alimentos Sanygran S.L., located in Tudela, Spain. The plant-based protein is commercially sold as ‘legumbreta fina’, and it is composed of soy flour (98%), beans flour, and rice flour.
Burger-making process
The study was conducted on burgers of three different formulations (i.e., a meat-based product, a plant-based product, and a hybrid product). The three burgers were made in the pilot plant of Food Sciences at UPNA. The plant-based ingredient was legumbreta fina, a commercially available extruded product made from mixed flours (soy, rice, and bean), and was obtained from a local manufacturer (Sanygran S.L., Navarra, Tudela, Spain). The protein is bought at Alimentos Sanygran S.L. and hydrated by the researchers working at UPNA in the same laboratories where the three burgers are prepared. The 69 g of the plant-based ingredient were soaked in 81 mL of water to prepare the plant-based burger (150 g), so that the product has a content similar to that of the meat-based burger. The plant-based burger is composed by legumbreta fina and water in the ratio specified in Table 2. The meat (Biceps femoris) used for preparing the veal-based and hybrid burgers in the study was derived from three bullocks produced under the conditions required by the Ternera de Navarra PGI hallmark. The hybrid burger (150 g) was prepared by mixing both meat (75 g) and plant-based legumbreta fina produced in Alimentos Sanygran S.L. and further re-hydrated at UPNA (75 g) in such a manner that the total composition of the product was maintained at 50% from both the animal and plant origins. All the three burgers have a final weight of 150 g. No more additional ingredients were considered in the formulation of the three burgers.
Table 2. Summary of the formulation of the three burgers under study, specifying the proportion of each ingredient relative to the final weight of each burger (150 g) in percentage terms, and the origin of each of the ingredients. n/a: not applicable.
Abbreviation: PGI, Protected Geographic Indication.
Water footprint assessment
The WF assessment of the three burgers under study was carried out following the guidelines set by ‘The Water Footprint Assessment Manual’ (Hoekstra et al., Reference Hoekstra, Chapagain, Aldaya and Mekonnen2011) and the ISO 14046 standard (ISO/TC 207/SC 5 Life cycle assessment, 2014). The WF calculations were expressed in the units of liters per burger and divided into the following three possible ways of impact: blue WF (quantifies the freshwater consumed from surface or groundwater systems), green WF (refers to rainwater that is incorporated into agricultural products), and gray WF (refers to contaminated water and is defined as the volume of freshwater that is required to assimilate a load of pollutants based on ambient water quality standards). The detailed WF results by phase and data sources are provided in Supplementary Material 1, matching the index shown in Fig. 1.
In the case of the meat burger, animal-breeding and burger-making processes were taken into account for the calculations of the WF (see Fig. 1). Within the animal-breeding phase, blue water consumption of the farm corresponded to service (cleaning and washing) and drinking water. The nitrogen-contaminated water derived from nitrate leaching in manure management was also taken into account, which constitutes the gray water of this process. Finally, for the animal-feeding WF, three different stages were taken into account. First, the water needed to mix the food, which consisted of blue water. Second, the WF of milk from the 4 milk-fed months was taken into account. Third, the WF of the feed was included. Feed composition and crop origin data can be seen in Table 3. In the case of milk and crops, the three forms of impact were separated: blue, green, and gray water. When needed, both economic (e.g., market value fraction) and mass (e.g., mass fraction) allocations were used to assign environmental loads to co-products and by-products. For that purpose, we followed the formulas indicated in ‘The Water Footprint Assessment Manual’ (Hoekstra et al., Reference Hoekstra, Chapagain, Aldaya and Mekonnen2011):
$$ \mathrm{WF} prod\;\left[p\right]=\left( WFproc\;\left[p\right]+\sum \limits_{i=l}^v\frac{WFprod\;\left[i\right]}{f_p\;\left[p,i\right]}\right)\;x\;{f}_v\left[\mathrm{p}\right]\;\left[\mathrm{volume}/\mathrm{mass}\right], $$
where
$ WFproc\;\left[p\right] $
corresponds to process WF,
$ WFprod\;\left[i\right] $
corresponds to the blue WF of the input byproduct,
$ {f}_p\;\left[p,i\right] $
is the byproduct mass fraction, and
$ {f}_v $
[p] is the economic value fraction (see Supplementary Materials 1 and 2).
Once the economic and mass allocations of the by-products were applied, all the WF data (liters per animal) for the meat burger were converted to the final unit (liters per burger), multiplying it by the carcass yield calculated. This refers to the percentage of the carcass weight (kg) of the calf that is attributed to the burger (liters per burger), and it was calculated as shown in the following formula (Hoekstra et al., Reference Hoekstra, Chapagain, Aldaya and Mekonnen2011):
$$ \mathrm{Carcass}\ \mathrm{yield}=\frac{TCw- BFw}{Burger\ patty\ weight\;(150g)}, $$
where TCw is the total carcass weight in grams and BFw is the burger fraction weight in grams used for the elaboration of the burger patty. In order to calculate the WF of the plant-based burger, three processes were taken into account along the supply chain (see Fig. 1). In the case of the protein-preparation stage, the blue water needed to produce the protein legumbreta fina was collected. These data were provided by Alimentos Sanygran S.L.U. In the case of the burger-making process, the blue water needed to hydrate the protein was counted. Finally, similar to the meat burger, the blue, green, and gray WFs of the different crops that constitute the plant-based protein were taken into account (see Table 4). The WF was calculated in liters per kilograms of crop and then multiplied by the quantity of each crop (kg) needed to produce the plant-based and hybrid burgers (see Table 1).
Table 3. Summary of the green, blue, and gray WFs of the crops used for feeding the calves, separated by country and expressed in liters per animal
Abbreviation: WF, water footprint.
Table 4. Summary of the green, blue, and gray water footprints of the crops used for making the plant-based protein, separated by country and expressed in liters per kilogram of crop
Abbreviation: WF, water footprint.
For the calculation of the WF of the hybrid, the same data were used. Given that the hybrid burger is made up of 50% plant-based protein and 50% animal protein, it was only necessary to apply this ratio to the previously calculated values of the WF of the plant-based and animal proteins.
The water consumption data and ingredient details for both feed and plant-based protein were sourced from farmers, food processors at UPNA, Alimentos Sanygran S.L.U., and the BEEF+ project (2020). The WF data come from Mekonnen and Hoekstra (Reference Mekonnen and Hoekstra2011, Reference Mekonnen and Hoekstra2012). When data in liters were unavailable, various databases and literature were used to find the equivalent factor. For more details on the sources, see Supplementary Material 1.
Carbon footprint assessment
The CF assessment of the three burgers under study was carried out following the guidelines set by the ISO 14067:2018 standard. To calculate the CF, the different gases emitted during the production of the burger were taken into account. Not only energy consumption but also methane emissions produced by livestock and nitrogenous gases derived from manure management were taken into account. To unify the units and express all the data in carbon dioxide equivalent per kilogram (CO2e/kg), the global warming potentials established by the IPCC guide were used (IPCC, 2005).
The detailed CF results by production phase and data sources are summarized in Supplementary Material 2, following the same index that was used to develop the flowchart (see Fig. 1).
Much of the CO2 emissions come from the energy consumption of infrastructures and processes needed to produce the burgers: (i) the energy consumption of the farm and the slaughterhouse for the meat and hybrid burgers, (ii) the energy consumption of the protein preparation for the plant-based and hybrid burgers, and (iii) the energy consumption of the cooking of the three burgers. Calculations were made by using the energy consumption in kilowatt-hour per burger (kWh/burger) of the infrastructures where the processes were carried out. In the case of legumbreta fina, an economic allocation was used to estimate the weight of its production in the total annual activity of the factory (Alimentos Sanygran S.L.U.). Once the data of the energy consumption were calculated, an emission factor in Kg CO2e/kWh of the electricity marketer of each building was applied (see Supplementary Material 2). Moreover, physical and economic criteria were used to allocate environmental loads to co-products and by-products, following the methodology indicated in the ISO 14067:2018 standard.
The CF of the crops needed to produce the feed for the calves (meat and hybrid burgers) and the plant-based protein (plant-based and hybrid burgers) was obtained from ADEME (2023). Most of the data were given in kg CO2e/kg. These emissions proceed from the fuel used in agricultural work, as well as the nitrogen oxides that are emitted from the soil by fertilization. Taking into account the composition of feed and the ratio of each crop within the plant-based vegetable protein, it was possible to calculate the amount of kilograms of CO2e emitted by each burger. Once the economic and mass allocations of the by-products were applied, all the CF data (kg CO2e/kg) for the meat burger were converted to the final unit (kg CO2e/burger), multiplying it by the carcass yield used for the WF calculations (see the ‘Limitations of the study’ section).
The data about the energy consumption and ingredient details for both feed and plant-based protein were sourced from farmers, food processors at UPNA, Alimentos Sanygran S.L.U., and the BEEF+ project (2020). The CF data come from ADEME (2023). When data in kg CO2eq were unavailable, various databases and literature were used to find the equivalent factor. For more details on the sources, see Supplementary Material 1.
Nutritional water and carbon productivity
Nutritional water productivity (NWP) and nutritional carbon productivity (NCP) refer to the efficiency with which agricultural systems convert carbon and water into edible food products, impacting food yield and resource use efficiency (Lal, Reference Lal2004; Ranganathan et al., Reference Ranganathan, Vennard, Waite, Lipinski, Searchinger and Dumas2016). This concept is important for assessing the sustainability of food production, as it considers how plants and animals utilize carbon and water to produce essential nutrients, such as fats, carbohydrates, and proteins. The NWP and the NCP were calculated by dividing the proximate composition (Supplementary Material 3) by the total WF (including the green, blue, and gray water components) and the CF of each burger. Moisture (ISO, 1997), protein (ISO, 1978), fat (ISO, 1973), and total ash contents (ISO, 1998) of the hybrid and plant-based samples, along with the flour used as raw material for the plant-based samples, were analyzed in duplicate (see Supplementary Material 3). The results were expressed in terms of productivity: g/l in the case of NW productivity and g/kg CO2e in the case of NC productivity. Three nutritional components were analyzed for each of the three burgers under study: proteins (ISO, 1978) (g), fats (ISO, 1973) (g), and carbohydrates (carbohydrates were calculated by difference, subtracting the sum of moisture, protein, fat, and ash from the total weight of the burger) (g). To compare different burgers with their nutritional water and carbon productivity (NWP and NCP), we used the following formula (Wen and Chen, Reference Wen and Chen2023):
$$ \mathrm{NWP}\;\mathrm{or}\ \mathrm{NCPi},\mathrm{n}\;\frac{= Pi,n}{WFPi\ or\ CFPi}, $$
where Pi,n is the gross production of each nutrient n of burger i and WFPi CFPi is the total WF and CF of the burger. The nutritional analysis was conducted using data from Ternera de Navarra PGI (Government of Navarra, 2004) and Alimentos Sanygran S.L.U. (Alimentos Sanygran S.L.U., 2022).
Results
The meat burger has a greater environmental impact in terms of WF and CF when compared with the other two burgers (see Fig. 2). It should be noted that the water needed to produce the beef burger was 1.8 times greater than the quantity needed to produce the hybrid burger and 21 times greater than that in the case of the plant-based burger. In turn, regarding the CF, the beef burger emitted approximately 2 times more kgCO2e along the supply chain when compared with the hybrid burger, and 13 times more than the plant-based one.
Figure 2. The water footprint (l/burger) and carbon footprint (kg CO2e/burger) of the three burgers under study: meat burger (beef), hybrid burger (50% beef and 50% vegetable—soy, beans, and rice), and plant-based burger (soy, beans, and rice).
Water footprint by component and production phase
As shown in Fig. 3, the three burgers have a higher green WF than blue or gray. The largest part of the green WF corresponds to the production of crops for animal feed and the raw material for the plant-based protein. The green WF refers to rainwater evapotranspirated and can be considered the least harmful component; it has lower environmental impacts on surface and groundwater bodies than the use of blue or gray WFs.
Figure 3. The water footprint (WF) (l/burger) of the three burgers under study, separated into green, blue, and gray WFs: meat burger (beef), hybrid burger (50% beef and 50% plant-based soy, beans, and rice), and vegetable burger (soy, beans, and rice).
Regarding the blue WF, in the case of the meat burger, the major part is related to the freshwater needed for feed production (380 l/burger). This includes the water needed to irrigate the crops and the mixing water for feed preparation. The plant-based burger’s blue WF, instead, is related in its great majority not only to the water needed to irrigate the crops (32 l/burger) but also to the water needed to hydrate the protein (0.114 l/burger) and the water incorporated in the burger making process (0.54 l/burger).
Finally, the major part of the gray WF corresponds to the crop production phase, which is translated into the nitrate pollution caused by fertilizer use. In the case of the meat burger, the decorticated oat flake needed to produce the animal feed has the highest gray WF (396 l/kg). in contrast, in the case of the plant-based burger, the beans flour used for the production of the plant-based protein has the highest gray WF among all the ingredients (938 l/kg). In all the cases, the hybrid burger has half the value of all the impact forms of WF, as it is produced in a ratio 50:50 of meat- and plant-based protein. In the case of all the three burgers, crop production is the stage in which more water resources are needed.
In the case of the meat and hybrid burgers, the animal production and growth phase represented 100% and 93%, respectively, of the total water used, from which approximately 84% came from feed preparation (see Fig. 4). This stage includes several processes: (i) milk-fed phase, (ii) feed production, and (iii) mixing water for feed preparation. Between them, the feed production had the greatest water consumption, particularly the crop growth for feed production. In the case of the plant-based burger, as it happened with the meat and hybrid burger, crop growth constituted the majority of the WF (99.6%) (see Fig. 4).
Figure 4. The water footprint (WF) of the three burger per production phase (left). The production phase with the highest water consumption of each burger is broken down per component (right). The data are represented as a percentage of the total WF, including the green, blue, and gray components. The first row corresponds to the meat burger, the second to the plant-based burger, and the third to the hybrid one.
Carbon footprint by production phase
The largest source of CO2 emissions in the meat burger production is the feed cultivation and preparation phase, amounting to 91% of the total GHG emissions (see Fig. 5). In the case of the plant-based burger, the major GHG emissions come from the crop cultivation stage (see Fig. 5). These emissions proceed from the fuel and energy used in the agricultural work, as well as the nitrogen oxides emitted by fertilization. The energy consumption derived from the slaughterhouse activities, industrial production of the plant-based protein, and cooking stage turned out to be negligible within the supply chain of the three burgers as it represented less than 1% of the total CF.
Figure 5. The carbon footprint (CF) of the three burgers per production phase. The data are represented as a percentage of the total CF. The first row corresponds to the meat burger, the second to the plant-based burger, and the third to the hybrid one.
Nutritional water and carbon productivity
The NWP of the plant-based burger was ~27 times greater in the case of proteins, ~14 times greater in the case of fats, and 150 times greater in the case of carbohydrates when compared with the meat burger, as shown in Fig. 6. The differences with the hybrid burger were lower, but still the NWP of the plant-based burger was ~13 (proteins), 11 (fats), and ~21 (carbohydrates) times greater.
Figure 6. The nutritional water productivity (left) expressed in g/l and the nutritional carbon productivity (right) expressed in g/kg CO2e for the three burgers under study. The nutritional WP includes the green, blue, and gray water footprints. The nutritional analysis was carried out analyzing proteins (first row), fats (second row), and carbohydrates (third raw).
In the case of the NCP, the plant-based burger’s protein, fat, and carbohydrate content was 15.4, 5.4, and 65 times greater, respectively, than that of the meat burger. In the case of the hybrid burger, the differences were also noticeable as the plant-based burger had a CP 7.4 times greater in the case of proteins, 4 times greater in the case of fats, and 13 times greater in the case of carbohydrates (see Fig. 6).
The big differences in protein and carbohydrate water and carbon productivity come from the fact that the legumbreta fina has a protein content of 50%, compared to 19% of the Ternera de Navarra PGI meat, and 15% of carbohydrates, compared to 1% of the carbohydrate content of the meat. Moreover, the fat content is similar in both products: 1.5% in the plant-based protein and 1.7% in the meat, respectively. However, the water use and the GHG emissions are considerably lower in the case of the plant-based burger (see Fig. 2), which makes the NWP and NCP of the plant-based burger still higher.
Discussion
Comparison with other studies and implications
Comparison with water footprint studies
The data of the WF of a meat burger obtained in the present study (3,871 l/burger, including the green, blue, and gray WFs) shows some differences with the WFs of other studies published in the literature. Hoekstra (Reference Hoekstra2012) calculated the mean WF of beef meat in Spain (2,684.6 l/kg meat). According to their results, a beef burger of 150 g has a WF equivalent to 4,026.9 l/burger. The main differences between the WF calculated by Mekonnen and Hoekstra (Reference Mekonnen and Hoekstra2012) and the one calculated in this study come from the green (3,592 vs. 2,447 l/burger) and the gray (233 vs. 1,035) WF components. These differences could be mainly due to differences in the composition of the feed taken as reference. Casado, Novo and Garrido (Reference Casado, Novo and Garrido2008) also analyzed the WF of cattle in Spain in 2006 and estimated that 17,450 liters of water are needed to produce 1 kg of beef meat. This means that 2,617 l/burger should be needed to produce a beef burger. In this study, they did not differentiate the three levels of impact of the WF (green, blue, and gray WFs). In addition to that, they used data from Canada to perform the calculations of the WF related to the feeding of the calves.
As other studies already stated (Peters et al., Reference Peters, Rowley, Wiedemann, Tucker, Short and Schulz2010; Hoekstra, Reference Hoekstra2012; Chaudhary and Tremorin, Reference Chaudhary and Tremorin2020; Arrieta et al., Reference Arrieta, Aguiar, González Fisher, Cuchietti, Cabrol, González and Jobbágy2022), the largest WF of animal production comes from the animal feeding phase, as seen in our study (see Fig. 5). The lower blue and gray WFs of Ternera de Navarra PGI beef are due to their mixed production system, where calves stay longer grazing rather than feeding. The composition, origin, and production system used for feed crops have a great impact in the final environmental load of the meat and other animal products (Wiedemann et al., Reference Wiedemann, Davis, McGahan, Murphy, Redding, Wiedemann, Davis, McGahan, Murphy and Redding2016). For example, as Ercin, Martinez-Aldaya and Ysbert Hoekstra (Reference Ercin, Martinez-Aldaya and Ysbert Hoekstra2011) already stated, the detailed assessment of the cultivation of crops is determinant in the freshwater use of a product. As far as we know, the studies cited above (Casado, Novo and Garrido, Reference Casado, Novo and Garrido2008; Peters et al., Reference Peters, Rowley, Wiedemann, Tucker, Short and Schulz2010; Hoekstra, Reference Hoekstra2012; Chaudhary and Tremorin, Reference Chaudhary and Tremorin2020; Arrieta et al., Reference Arrieta, Aguiar, González Fisher, Cuchietti, Cabrol, González and Jobbágy2022) do not have detailed information about the origin and production systems used to produce feed crops. In fact, using locally produced crops and agriculture by-products can substantially reduce the WF of an animal product, as the by-products, according to the economic allocation for the environmental burdens, have a water and CFs equal to zero.
The plant-based alternatives appeared to be the most environmentally sustainable in terms of water resource use. Smetana et al. (Reference Smetana, Mathys, Knoch and Heinz2015) analyzed the environmental performance of the most commonly used meat substitutes and the study revealed that the plant-based proteins are more sustainable than insect or mycoprotein-based analogues. Similar to our study, Ercin, Martinez-Aldaya and Ysbert Hoekstra (Reference Ercin, Martinez-Aldaya and Ysbert Hoekstra2011) determined that beef meat burgers have a much larger WF than soy-bean analogues. According to these authors, the WF of a 150 g soy burger is 158 l, a bit less than the 184 l of our study. The variations in WF results for beef and plant-based burgers arise from differences in production systems, boundaries, and data sources, requiring specific system information for more accurate estimations.
In relation to the hybrid options, literature scarcity makes it difficult to compare the results with other studies. However, a study carried out by Chaudhary and Tremorin (Reference Chaudhary and Tremorin2020) determined that 33% replacement of ground beef with cooked lentil puree can decrease the blue water use by ~33%. Hybrid options are little studied and are interesting both at an environmental level and a nutritional level.
Considering the differences observed in the WF of the three types of burgers in this study (plant-based, meat, and hybrid), several strategies could be applied to reduce their impact. For the beef burger, sourcing local feed ingredients would decrease the green, blue, and gray WFs. Strategies such as regenerative agriculture, which enhances soil water retention, and dietary supplements, which reduces cattle water intake, could contribute to a lower WF. Additionally, the inclusion of vegetal by-products for cattle feed (González-Martínez et al., Reference González-Martínez, Goenaga, León-Ecay, de las Heras, Aldai, Insausti and Aldaya2024) could also significantly reduce the overall WF. For the plant-based burger, selecting drought-resistant crops or improving irrigation efficiency could further reduce its WF. In the case of the hybrid burger, incorporating plant ingredients with lower water demands—such as legumes requiring less irrigation—while also reducing the meat proportion could significantly decrease both green and blue WFs. Further studies should focus on optimizing production systems to improve water management and sustainability.
Comparison with carbon footprint studies
According to the present study, the Ternera de Navarra PGI meat burger has a lower CF when compared with global mean data, amounting to 2.1 kgCO2e. A recent study by Saget et al. (Reference Saget, Porto Costa, Santos, Vasconcelos, Styles and Williams2021) about the life cycle analysis of beef burger patties revealed that a burger emits 4.5 kgCO2e in Ireland and 6.6 kgCO2e in Brazil. According to the data obtained in this study, the meat burger produced with Ternera de Navarra PGI emits two times and three times less kgCO2e than Irish or Brazilian burgers, respectively. These differences are probably due to the fact that the Ternera de Navarra PGI uses a mixed production system (Table 1) compared to the intensive model of the other studies. Globally, beef’s cured meat CF is settled in 36 kg CO2e/kg (Ritchie, Reference Ritchie2020), which is the equivalent to 5.4 kg CO2e/burger.
According to other similar studies (Fiala, Reference Fiala2009; FAO, 2010; Desjardins et al., Reference Desjardins, Worth, Vergé, Maxime, Dyer and Cerkowniak2012; Arrieta et al., Reference Arrieta, Aguiar, González Fisher, Cuchietti, Cabrol, González and Jobbágy2022), the major contributors to the GHG emissions of meat production are methane (CH4) emissions coming from enteric fermentation and feed cultivations and preparation processes. It is estimated that approximately 50% of the GHG emissions come from the enteric fermentation and 16% from feed production (FAO, 2010; Desjardins et al., Reference Desjardins, Worth, Vergé, Maxime, Dyer and Cerkowniak2012). However, the methane emissions in cattle depends, to a great extent ,on the farming system used and the pasture management (Deramus et al., Reference Deramus, Clement, Giampola and Dickison2003). Moreover, other studies realized that feed cultivation and preparation can have the greatest environmental load in the case of feedlot-finished systems (Schroeder, Kluwe Aguiar and Baines, Reference Schroeder, Kluwe Aguiar and Baines2012). The meat studied comes from a hybrid system where calves are fed both by grazing and feed. Due to the cold climate in northern Navarra, which limits grazing for several months, most of the environmental load of the burger is expected to come from feed production and manure management, particularly nitrogen gases. In addition, the feed-intake efficiency and diet composition are determining factors in CH4 emissions produced during ruminant’s digestion (Lassey, Reference Lassey2001; Beauchemin and McGinn, Reference Beauchemin and McGinn2006; Honan et al., Reference Honan, Feng, Tricarico and Kebreab2021).
Most of the CF derived from crops comes from the use of fertilizers, machinery, and the use of forest land that prevents more CO2 from being fixed. In the case of the plant-based burger, this impact was smaller because producing the plant-based burger requires only 150 g of crops, whereas producing the meat burger requires ~1 kg of crops. Few studies were found to compare the environmental performance of hybrid options. The results presented by Chaudhary and Tremorin (Reference Chaudhary and Tremorin2020) suggested that the GHG emissions of a lentil and beef-based burger (30%–70%) were reduced by ~33% compared with a normal beef burger.
Considering the differences in the CF observed across the three burger types (plant-based, meat, and hybrid), promoting the mixed feeding system used for Ternera de Navarra PGI could significantly reduce the CF of beef burgers. Extending the grass-feeding period and optimizing pasture use in the IGP Ternera de Navarra system—where cattle feeding is mixed—could further reduce the CF, as grass-fed systems have been shown to be more climate-friendly (Gagelman and Norwood, Reference Gagelman and Norwood2018). For plant-based burgers, further improvements in agricultural practices, such as reducing the use of fertilizers (Hillier et al., Reference Hillier, Hawes, Squire, Hilton, Wale and Smith2009) or adopting conservation tillage methods (Fathi et al., Reference Fathi, Tari, Amoli and Niknejad2020), could contribute to reducing the GHG footprint of crop production. Hybrid options could offer a promising alternative by reducing the need for animal-based products, thereby lowering emissions from beef production.
Comparison with nutritional productivity studies
Our study provides a detailed comparison of NWP and NCP across plant-based, hybrid, and meat burgers, offering new insights into alternative proteins. While existing research (Poore and Nemecek, Reference Poore and Nemecek2018; Gibbs and Cappuccio, Reference Gibbs and Cappuccio2022) highlights the environmental benefits of plant-based foods, our findings offer a comparative analysis of NWP and NCP across proteins, fats, and carbohydrates, which is less commonly explored (Renault and Wallender, Reference Renault and Wallender2000; Khan and Hanjra, Reference Khan and Hanjra2009; Casson et al., Reference Casson, Giovenzana, Beghi, Tugnolo and Guidetti2019). NWP refers to the amount of nutritional output (e.g., grams of protein, fat, or carbohydrates) per unit of water used, whereas NCP measures the nutritional yield per unit of CO₂ emissions. These indicators allow for deeper evaluation of food sustainability beyond traditional environmental assessments.
Consistent with previous studies (Renault and Wallender, Reference Renault and Wallender2000; Blas et al., Reference Blas, Garrido, Unver and Willaarts2019), our results show that plant-based foods are more productive in terms of water use than animal food products. Since Renault and Wallender (Reference Renault and Wallender2000) developed the Water Footprint Productivity Index , few studies have used this measure to assess the environmental sustainability of food products. To the best of our knowledge, no studies have assessed the nutritional carbon footprint productivity. Due to the lack of literature about these indexes, comparing our results with other similar studies remains a challenge.
Our study highlights the hybrid burger as a sustainable middle ground between plant-based and meat-based options. While the plant-based burger excels in nutritional water and carbon productivity, the hybrid burger offers significant improvements over meat in terms of resource efficiency, with protein, fat, and carbohydrate productivity 11–21 times greater for NWP and 4–13 times greater for NCP. Beyond macronutrient productivity, fiber and micronutrients play a crucial role in dietary health. Plant-based foods are higher in fiber, which has been linked to improved digestion and cardiovascular benefits (Slavin, Reference Slavin2005). In contrast, meat is a primary source of vitamin B12, an essential nutrient absent in plant foods and often requiring fortification in vegetarian diets (Watanabe et al., Reference Watanabe, Yabuta, Bito and Teng2014). Additionally, fat composition differs between these products; plant-based options typically contain higher unsaturated fat and lower saturated fat, which may reduce cardiovascular risk (Mensink et al., Reference Mensink, Zock, Kester and Katan2003). Hybrid formulations can balance these differences, maintaining a favorable fatty acid profile while preserving the sensory characteristics of meat. Given these variations, a broader assessment of micronutrient content and calorie productivity would provide a more comprehensive understanding of the nutritional and environmental trade-offs of alternative protein sources.
According to our results, the plant-based burger is richer in proteins and more productive in terms of water use and CO2 emissions. However, nutritional adequacy is not only determined by protein content but also by amino acid (Aa) composition, digestibility, and overall nutrient density. The amino acid profile refers to the types and amounts of amino acids in a protein, indicating its overall nutritional quality. Unlike meat, plant proteins may lack some essential amino acids. However, as Young and Pellett (Reference Young and Pellett2018) highlight, plant proteins can provide a complete Aa profile when appropriately combined (e.g., grains and legumes). Additionally, plant-based proteins tend to have lower digestibility (85%–87%) than animal proteins (≈100%), which should be considered when evaluating their nutritional value.
Limitations of the study
The current study has a number of limitations and uncertainties due to a lack of data, which can limit the accuracy of the results. First of all, to determine whether one burger is a preferable option over another, it is crucial to conduct a thorough WF assessment that goes beyond quantifying the green, blue, and gray WF volumes. This evaluation should include an examination of water scarcity and pollution levels in the areas where the production process occurs. In addition, average data for typical farming systems in Navarra were used, ignoring the fact that production system practices and diet composition can be different from farm to farm. Another potential limitation of these kinds of studies arises from the reliance on secondary data (in our case study, for the ingredients involved in feed production). Given the regional variations in agricultural practices and ingredient sourcing, there is a possibility of bias due to differences in the data sources. To strengthen the reliability of future findings, it would be advisable for future studies to conduct sensitivity analyses on the choice of databases, exploring how variations in data sources may influence the results.
Additives
There are a series of additives that are added both to feed and to plant-based burgers, for which neither WF nor CF data can be found. In the case of feed, there was one ingredient for which no information was obtained (soy husk), and several additives whose origin and the water and energy consumption involved in their manufacture were unknown: calcium carbonate, salt, corrector, calcium bicarbonate, and buffer.
The plant-based protein legumbreta fina used for the current study was hydrated and processed to make it similar to a burger. However, there are several additives, such as gums, salt, aromas, emulsifiers, and stabilizers, that need to be added to make the plant-based burger suitable for consumption, with a texture and sensory profile similar to a traditional burger.
While these additives are generally recognized as safe by food safety authorities, like the FDA, their inclusion contributes to a level of processing, which has raised concerns regarding the classification of some plant-based alternatives as ultra-processed foods (Monteiro et al., Reference Monteiro, Cannon, Levy, Moubarac, Louzada, Rauber, Khandpur, Cediel, Neri, Martinez-Steele, Baraldi and Jaime2019). Recent studies suggest that frequent consumption of ultra-processed foods may be associated with an increased risk of non-communicable diseases, such as cardiovascular disease, obesity, and metabolic disorders (Pagliai et al., Reference Pagliai, Dinu, Madarena, Bonaccio, Iacoviello and Sofi2021; Srour et al., Reference Srour, Kordahi, Bonazzi, Deschasaux-Tanguy, Touvier and Chassaing2022).
Similarly, additives used in animal feed, including preservatives, binding agents, and mineral correctors, may have environmental impacts that remain largely unquantified. These products, often synthesized in industrial settings, likely entail additional water and carbon costs that are currently unknown. Further studies should evaluate the full environmental footprint of these ingredients, as well as their potential health implications in the case of plant-based alternatives.
Transport
On the other hand, the limits established in the present study (see the ‘Comparison with other studies and implications’ section) for the calculation of the WF and CF did not contemplate transportation. The main reason for not including transport in the calculations was the great uncertainty derived from the lack of information. Despite knowing the origin of the ingredients of both the feed and the plant-based burgers, the method of transport used (e.g., air, car, and boat) was unknown. In addition, this study was carried out using a typical farm system from the northern part of Navarra without taking into account any specific farm. Thus, real distances between the farm, the slaughterhouse, and the University (UPNA) could not be estimated. While the WF related to transport should be considered, there are no mean values available to estimate the water load associated with local, national, or international distances. It should be noted that most of the ingredients imported are transported by air, which primarily relies on fossil fuels. According to Hoekstra et al. (Reference Hoekstra, Chapagain, Aldaya and Mekonnen2011), fossil fuels have a smaller WF compared with biofuels, as the water use is limited to the colling and refining processes. However, it was decided to carry out a simulation of what the CF would be if the emissions caused by the transport of the ingredients of both the feed and the plant-based burgers were included. The emission factors used for the calculations of GHG emissions from transport were the ones established by ECODES (2019) and are separated into three categories: local, national, and international.
According to the results, transport had a major impact in the CF of the meat and hybrid burgers (see Fig. 7). This is due to the origin and quantity of the ingredients needed to produce the feed. The feed is composed by six different ingredients from which four of them are produced and transported out of the country (corn, DDG corn, soy 47, and palm oil). In fact, when the transport of ingredients was considered, the CO2 emissions were estimated to increase by 8% in the case of the meat burger.
Figure 7. Comparison between the carbon footprint in kg CO2e of each burger when taking into account the transport phase (black) and when not (gray).
In the case of the plant-based burger, three crops are needed, and two of them are produced and transported nationally, which significantly reduces the CF associated with the transportation.
Carbon fixation
Another limitation of the system comes from the carbon fixation uncertainties. According to previous research (Soussana, Tallec and Blanfort, Reference Soussana, Tallec and Blanfort2010; Alonso, Reference Alonso2011), pastures are great carbon sequestration sinks, and depending on the soil management, climate, and agricultural practices, they can fix large amounts of CO2. Hammar, Hansson and Röös (Reference Hammar, Hansson and Röös2022) estimated that the carbon sequestration rate of temperate grasslands in Sweden was approximately 0.2 Mg C ha−1 yr−1. It has been estimated that carbon sequestration by pastures can mitigate the GHG emissions of beef production from 22% (Hammar, Hansson and Röös, Reference Hammar, Hansson and Röös2022) to 34% (Soussana, Tallec and Blanfort, Reference Soussana, Tallec and Blanfort2010). However, it is difficult to find environmental assessment studies of meat products in which this parameter is included. Moreover, a recently published study underscores marked regional variations in net soil GHG balances, highlighting the need for spatially explicit assessments in other regions (Michailidis et al., Reference Michailidis, Lugato, Panagos, Grados, Freund, Jones and Abalos2025). A recent study by Saget et al. (Reference Saget, Porto Costa, Santos, Vasconcelos, Styles and Williams2021) included the carbon opportunity costs in their comparison between the environmental performance of beef and plant-based patties from Brazil and Ireland. It was seen that cattle needed large land requirements when compared with plant-based protein production, which consequently makes carbon sequestration and emission rates proportionately higher in meat products. On the other hand, it was also difficult to obtain carbon fixation rates from the crops needed to produce the feed and plant-based burgers. Other authors analyzed the global carbon fixation data for different crops (Mathew et al., Reference Mathew, Shimelis, Mutema and Chaplot2017). As it occurs with pastures, depending on the agricultural practices, the climate and other geographic and physiologic factors, the carbon fixation rate of each crop varies from one country to another. A study carried out in the northern part of Navarra (Lo et al., Reference Lo, Blanco, Canals, González de Andrés, San Emeterio, Imbert and Castillo2015) stated that the conversion from arable to grassland could lead to an increase in 10 Mg soil C ha−1. Moreover, Mathew et al. (Reference Mathew, Shimelis, Mutema and Chaplot2017) realized that natural grasslands and cereals had higher carbon sequestration yields when compared with most agricultural crops. Further research is needed so that CF studies include this parameter in the environmental assessment of both, especially for beef LCA.
Conclusions
The present study on different types of burgers produced in Navarra, Spain, shows that beef burgers have higher carbon and WFs compared with plant-based and hybrid alternatives. The animal production and growth stages were identified as the ones with the greatest environmental impacts, with feed preparation contributing significantly to both water use and GHG emissions across the supply chain. The plant-based burger showed to be the most water and carbon friendly burger under study. The hybrid burger offers a significant improvement in water and carbon productivity while maintaining the nutritional balance compared with the beef burger. However, uncertainties in the data and methodological constraints should be acknowledged when drawing conclusions. Future research could also extend the LCA to additional impact categories or conduct consequential LCAs to assess market-driven effects. In order to capture tradeoffs and/or synergies between different environmental aspects, a comprehensive footprint family assessment is essential (Vanham et al., Reference Vanham, Leip, Galli, Kastner, Bruckner, Uwizeye, van Dijk, Ercin, Dalin, Brandão, Bastianoni, Fang, Leach, Chapagain, Van der Velde, Sala, Pant, Mancini, Monforti-Ferrario, Carmona-Garcia, Marques, Weiss and Hoekstra2019).
Supplementary material
The supplementary material for this article can be found at http://doi.org/10.1017/S1742170525100112.
Acknowledgements
We would like to thank Isabel Velázquez, Alimentos Sanygran S.L., Rasmi Janardhanan (Marie Sklodowska-Curie Grant Agreement No. 801586), UPNA, Irantzu Goenaga, TRASA, and Kizkitza Insausti (UPNA, from BEEF+); Pablo Manzano (BC3); Olivia Barrantes-Díaz (Universidad de Zaragoza); Jose Mari Ayerra (Ternera de Navarra PGI); and Mesfin Mekonnen (University of Alabama) for providing data necessary for the performance of the current study. Open access funding provided by Universidad Pública de Navarra.
Funding statement
The project leading to these results received funding from ‘la Caixa’ and the Caja Navarra Foundation under Agreement LCF/PR/PR13/51080004.
Competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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