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INTRODUCTION
As incomes have risen and the population has become increasingly urbanized, diets and meal plans have changed, with an increased consumption of processed foods and meat. This transition of dietary habits has affected human health and the environment [1]. To maintain a sustainable environment and overall health, there has been a move toward eco-friendly food and some individuals have refrained from consuming animal-based foods [2]. As a result, vegan diets that contain no animal-based items have been increasing in popularity [2]. Many vegans have made nutritional choices with the aim of taking better care of the global environment, animal welfare, and the health advantages of a plant-based diet [3]. The production of food items from an animal source is associated with higher greenhouse gas (GHG) emissions than the production of plant-based food items because energy is lost at each trophic level [4,5]. When considering global GHG emissions by economic sector, the Agriculture, Forestry and Other Land Use sector accounts for 24% of the total [6]. According to the Food and Agriculture Organization of the United Nations (FAO), livestock contribute to nearly two-thirds of agricultural GHG emissions and 78% of agricultural methane emissions. Using the Global Livestock Environmental Assessment Model (GLEAM), emissions from feed crops account for approximately 45% of the total emissions from livestock, and methane and nitrous oxide from manure account for approximately 10% of total GHG emissions [7].
In this study, we used a common suggested meal plan SMP based on a Korean food menu and a vegan meal plan (VMP), which represented the SMP with all animal products substituted for alternatives. In Fig. 1 using these meal plans, the GHG emissions per kcal, GHG emissions per protein, and GHG emissions per amino acid were compared. We also considered the nutritional value of the SMP and VMP.
The amount of GHG emissions can be converted to a CO2 equivalent (CO2e) in food, largely based on the energy content (MJ) of the products or the functional unit; i.e., 1 kg for most products [8]. However, meat or animal products are consumed because they are nutrient dense rather than for providing energy, and they typically contain proteins with all amino acids and micronutrients, such as iron (Fe), zinc (Zn), selenium (Se), vitamin D, and vitamin B12 [9–11]. Some studies consider the GHG emissions related to foods, but they didn’t consider GHG emissions with their nutrients and nutritional values [5,12,13]. It is therefore irrational to evaluate GHG emissions from meat on the basis of energy provided (kcal) rather than the amounts of protein or other micronutrients (g or μg). Functional units, such as GHG emissions (g CO2e) per protein (g), GHG emissions (g CO2e) per amino acid (mg), and GHG emissions (g CO2e) per vitamin B12 (μg), are rarely considered [10,11].
MATERIALS AND METHODS
The subjects of the study were adult men, over the age of 19, who had entered the post-high school stage of education, because their nutritional requirements were higher than other ages and genders [14]. Table 1 shows the content of the meal plans prepared according to the one day meal plan of the National Institute of Agricultural Sciences meal plan menu [14,15]. In the meal plan database, the age range is set from 19 to 29. The meal plan menu was divided into two categories: (1) the SMP, including animal products, such as meat and eggs, and (2) the VMP, which was based on the SMP, but animal-based protein sources, such as beans and tofu, were substituted for meat alternatives. To ensure the nutrient adequacy of each meal plan, the nutrient content was assessed against the ‘9th Korean Food Composition Tables I and II published by the National Academy of Agricultural Science under the Rural Development Administration (RDA) [14–17].
Carbohydrates and proteins were selected as macronutrients, but fats were not considered because they were not included in the recommended intake. Proteins were subdivided into total amino acids, essential amino acids, and non-essential amino acids. To compare the macronutrients, the recommended intake was obtained from the ‘Dietary Reference Intakes For Koreans 2015’ (DRI 2015) to determine a standard value [14]. According to DRI 2015, the estimated energy required for adult men aged 19–29 is 2,600 kcal/day, with carbohydrates accounting for 55% of the total food intake, and the suggested intake for proteins is 65 g/day. Although the recommended intakes of various amino acids are available in the DRI 2015, in the ‘9th Korean Food Composition Tables I and II’ published by the National Academy of Agricultural Science under the RDA, there is no specific nutritional intake level for each amino acid. Therefore, only the categories of total amino acids, essential amino acids, and non-essential amino acids were considered.
In Table 2, vitamin A, vitamin D, vitamin B12, calcium (Ca), Fe, magnesium (Mg), phosphorus (P), potassium (K), sodium (Na), Zn, and folic acid were selected as micronutrients, all of which have recommended indicators. Their levels differed between the SMP and VMP. The levels of vitamins A, D, and B12 in the VMP were 0 μg. The recommended intake of each nutrient was 800 μg/day for vitamin A (retinol), 2.4 μg/day for vitamin B12, 800 mg/day for Ca, 10 mg/day for Fe and Zn, 350 mg/day for Mg, 700 mg/day for P, and 400 μg dietary folate equivalent/day for folic acid. The intakes of Na and K were 2,000 and 3, 500 mg/day, respectively, with these values based on sufficient intake and not recommended values [14,18]
Adapted from the ‘Dietary Reference Intakes For Koreans 2015’ (DRI 2015) [14].
Table 3 shows the carbon footprint of food items from The Foundation of Agriculture Technology Commercialization and Transfer (FACT), which were used to calculate GHG emissions for the VMP and SMP. In the FACT report, Toram Inc. used life cycle inventory database from Eco-invent (Switzerland) and LCA food (Denmark) to utilize the Life Cycle Assessment (LCA). There were four stages in the calculation of GHG emissions for food. First, food production was classified into three steps: (1) a preparation step, including seeding, herbicide and fertilizer use, water consumption, and use of fossil fuels; (2) a production step that could use organic or conventional methods; (3) a processing step, which involved consideration of additives, processing, packaging, transport, and storage. Second, there was a transport stage, in which land transportation by truck was selected. The average transportation distance was taken as 180 km from production site to the sale site [19]. Third, there was a consumption stage, which involved the use of liquefied natural gas, and a standard cooking time and heating power were selected to calculate GHG emissions. Finally, there was a disposal stage, but this was excluded because the resulting values were unreliable and accounted for only a small share of the total emissions [20].
With the meal plans and GHG emissions data, GHG emissions per nutritional value, especially calories (kcal) and proteins (g), were calculated. GHG emissions and nutritional value of the SMP was set as a standard to compare against the VMP.
RESULTS AND DISCUSSION
As shown in Fig. 2, the SMP was used as the standard to compare the relative GHG emissions per calorie with the VMP GHG emissions per calorie. The SMP GHG emissions per calorie were 1.253 g CO2e/kcal, while for the VMP the corresponding value was 1.027 g CO2e/kcal. Therefore, the VMP emissions per calorie were 18% lower than the SMP GHG emissions per calorie. GHG emissions from the SMP, which contained animal products, were greater than those from the VMP, but there was insufficient meal plan data to determine if the difference was statistically significant [10]. Table 4 shows the levels of proteins and amino acids in the diets. Based on these values, the GHG emissions per protein (g CO2e/g) in the SMP were calculated to be 31.75 g CO2e/g, while for the VMP the corresponding value was 40.85 g CO2e/g. The GHG emissions per essential amino acid (g CO2e/mg) in the SMP were 0.06 g CO2e/mg, while for the VMP the corresponding value was 0.12 g CO2e/mg, as shown in Table 4. The VMP emitted more GHGs under both conditions, but the specific origin of the protein source and essential amino acids should be considered [10,21]. For example, the sources of proteins and amino acids from animal products include eggs, beef, pork, chicken, fish, and milk. The sources of proteins and amino acids from plants include soybeans, tofu, barley, and brown rice. However, plant-based proteins or amino acids are incomplete sources and need to be mixed with animal products or consumed in large amounts to meet the recommended intake, otherwise supplements should be taken to meet the shortfall [14]. These results indicated that even when a meal plan includes some animal products, its GHG emissions may not be higher than a plant-based meal plan. Table 5 shows that the amount of vitamins A, D, and B12 in a VMP diet is 0 μg, whereas in an SMP diet the respective amounts are 83.12, 17.62, and 4.48 μg, indicating that these vitamins should be obtained by taking supplements when following the VMP diet. GHG emissions data for vitamin or amino acid supplements were not available and therefore it was not possible to make a comparison between diets that included supplements.
| VMP | SMP | |
|---|---|---|
| GHG emissions per protein (g CO2e/g) | 40.85 | 31.75 |
| GHG emissions per amino acid (g CO2e/mg) | 0.12 | 0.06 |
From a health perspective, a vitamin A deficiency can lead to abnormal development and growth in humans, particularly in the immune system [17]. Vitamin D helps the body absorb Ca, Mg, and P, which is important for normal bone development and maintenance. With a vitamin D deficiency, rickets and osteoporosis can occur in children and adults, respectively [18,22,23]. Vitamin B12 deficiency can lead to pernicious anemia and neurological disorders, such as delayed brain growth, spinal degeneration, and poor intellectual development [17,18,24,25].
Table 6 shows that the SMP provided 2.13 times more amino acids than the VMP, with 2.25 times more essential amino acids and 2.03 times more non-essential amino acids. A long-term VMP diet would likely result in a deficiency of essential and non-essential amino acids. This would weaken the immune system and increase the likelihood of developing various diseases. Among the essential amino acids, methionine deficiency can affect body weight and eating patterns [14,21].
Fig. 3 compares the micronutrient total intake with the recommended intake for the two meal plans. For both meal plans, Ca and Zn intake did not reach the recommended amount. If this condition persists, there is a risk that bone density will decrease, leading to osteoporosis. In addition, a continuous low intake of Ca may result in exposure to various health conditions, such as cardiovascular disease, degenerative joint disease, and neurodegenerative disease [14,26]. Zn deficiency is related to growth disorders, loss of appetite, diarrhea, vomiting, and inflammation. Excessive Zn uptake prevents the absorption of other micronutrients and weakens the immune system [14,26]. The other micronutrients exceeded the recommended intake in both the VMP and SMP.
CONCLUSION
When comparing the SMP and VMP in terms of the quantification of GHG emissions, the SMP resulted in higher GHG emissions than the VMP, but this could change depending on the type of food selected in the diet. Further studies are required to investigate the variation in GHG emissions between different meal plans based on the different amounts of proteins or amino acids in the diets, and by considering daily meat intake per person.
In terms of health concerns, the SMP contains large amounts of amino acids, vitamin D, and vitamin B12, but a VMP diet cannot deliver the recommended intake. It could possibly lead to amino acid, vitamin D, or vitamin B12 deficiency, with a need to consume multivitamin supplements or amino acid additives. It is therefore necessary to consider if the production of supplements emits GHGs.
There is a need to establish LCA data related to various supplements, which would enable a comparison of GHG emissions between individuals that consume supplements with a VMP and those eating an SMP, which might lead to an increase in GHG emissions by vegans. LCA data are not currently available for all ingredients, and for the more eco-friendly meal plans further research is needed to establish a specific database for additional meals. Plus, for the credibility issues, further research need to be conducted about the women of the same age. Such a study could provide reasons why animal products should be consumed. Because of the growing interest in other environmental impacts, such as nitrogen and water footprints, these issues should be examined in the near future.
