ABSTRACT
Plant-based diets in comparison to diets rich in animal products are more sustainable because they use many fewer natural resources and are less taxing on the environment. Given the global population explosion and increase in wealth, there is an increased demand for foods of animal origin. Environmental data are rapidly accumulating on the unsustainability of current worldwide food consumption practices that are high in meat and dairy products. Natural nonrenewable resources are becoming scarce, and environmental degradation is rapidly increasing. At the current trends of food consumption and environmental changes, food security and food sustainability are on a collision course. Changing course (to avoid the collision) will require extreme downward shifts in meat and dairy consumption by large segments of the world’s population. Other approaches such as food waste reduction and precision agriculture and/or other technological advances have to be simultaneously pursued; however, they are insufficient to make the global food system sustainable. For millennia, meatless diets have been advocated on the basis of values, and large segments of the world population have thrived on plant-based diets. “Going back” to plant-based diets worldwide seems to be a reasonable alternative for a sustainable future. Policies in favor of the global adoption of plant-based diets will simultaneously optimize the food supply, health, environmental, and social justice outcomes for the world’s population. Implementing such nutrition policy is perhaps one of the most rational and moral paths for a sustainable future of the human race and other living creatures of the biosphere that we share.WHAT ARE SUSTAINABLE DIETS?
Definitions of sustainability generally address aspects of ecology, economy, and society and have different meanings depending on the context. A sustainable diet will not necessarily be defined the same way for consumers as for farmers or food manufacturers. In 2010 the FAO defined sustainable diets as “those diets with low environmental impacts which contribute to food and nutrition security and to healthy life for present and future generations. Sustainable diets are protective and respectful of biodiversity and ecosystems, culturally acceptable, accessible, economically fair and affordable; nutritionally adequate, safe and healthy; while optimizing natural and human resources” (1). Furthermore, according to Fanzo et al (2), the determinants of a sustainable diet are as follows: nutritional adequacy, environmental sustainability, cultural acceptability, and low-cost accessibility.
In the arena of environmental sustainability, the focus of this article, 2 important dimensions are considered: efficiency and environmental protection. Efficiency is a measure of how natural resources are used to obtain the foods of a given diet and is quantified by the ratio of inputs to outputs. Environmental protection addresses the preservation of ecological systems that allow life on earth: the biosphere. It is measured by environmental indicators such as global warming potential, biodiversity, and eutrophication. Thus, both key dimensions of environmental sustainability, the efficient use of natural resources, and the avoidance of environmental degradation in the production, preparation, and disposing of the food consumed are to be considered in assessing the sustainability of a diet.
ARE CURRENT FOOD PRODUCTION AND CONSUMPTION PATTERNS SUSTAINABLE?
Evaluating the food systems in light of these 2 dimensions provides a framework for assessing the environmental sustainability of current practices. The basic inputs and outputs of the food system as a whole are shown in Figure 1. The food system takes inputs from the natural world in the form of natural resources—that is, land, sun radiation, water, fossil energy, and chemicals. Working together, these aforementioned inputs produce food for human societies. Food is the desired output of the system; however, the food system also produces undesirable outcomes in the form of solid, liquid, and gas waste. Societal demand, which includes consumer preferences, is a major driver of the food system (3). The life cycle of foods is determined by the production, processing, transportation, storage, retail, and disposal practices used; and consumer demands in a given society define these interactions within the food system.Agriculture is the practice of producing crops and raising livestock. From an ecological perspective, agriculture involves managing resources to capture solar energy and the transferring of it to people for their use. For millennia, agriculture was a spatially complex system of polycultures, and a variety of crops and animals inhabited the same farm lands. Compared with output (food produced), inputs were low and consisted of solar energy, rain water, and animal waste for fertilizer (4). By efficiency standards, the system was sustainable. With the advent of industrial agriculture, farms became a monoculture enterprise, with a single farm generally producing a single food item (5). The main inputs are nonrenewable energy from fossil fuel and high amounts of chemicals, and oil is also used to produce nitrogenous fertilizers and irrigation water (5). These enormous inputs of energy in modern agricultural practices have greatly increased food production but have resulted in an energy imbalance.
The increase in energy usage for food production from traditional to current practices is depicted in Figure 2. Originally, agricultural activity resulted in a net gain in energy as more energy was obtained from food than expended on its production. One farmer could feed a family by using only the energy of his labor and that provided by nature. As food production intensified with the use of fossil fuel energy, the ratio increased for the energy input to energy output from food (6). The imbalance between the total energy required by the US food system and the total food energy produced by the effort was reported by the Center for Sustainable Systems (7). On-farm production amounts to 21% of the total system energy usage, and 40% of agriculture production energy go into making chemical fertilizers and pesticides. Large amounts of energy go into processing, transporting, storing, and serving food. For every 10.3 quads of the total energy used to produce food, only 1.4 quads of food energy is created, yielding an overall energy efficient ratio of >7:1 (7). From the energy perspective, the industrial food system is very inefficient and because most of the energy inputs are from nonrenewable sources such as fossil fuels, the current system is unsustainable (5).EFFICIENCY: ANIMAL COMPARED WITH PLANT FOODS
Raising animals for human food is an intrinsically inefficient process. As we move up in the trophic chain there is a progressive loss of energy. Grass-fed livestock subsists, but this is not the main source of meat for human consumption in developed nations. Modern husbandry (animal farms) is based on intensive feeding of grain crops to animals (5). This grain could be a source of food for humans. The same standards apply to the production of other animal products such as eggs and dairy. Several authors have computed the efficiency ratios of animal compared with plant foods for human consumption. The amount of grain needed to produce the same amount of meat varies from a ratio of 2.3 for chicken to 13 for beef (Table 1). Pimentel and Pimentel (8) established that, on average, 11 times greater fossil energy is required to produce animal protein than plant protein for human consumption. However, the energy-to-protein efficiency ratio varies greatly by type of meat. More specifically, it is only 4 times greater for chicken protein compared with grain protein but 40 times greater for beef protein compared with grain protein. We have previously reported that the ratio for water used in the production of soy protein compared with the same quantity of animal protein is from 4 to 26 and showed that the ratio between soy protein and the different types of animal proteins varies from 6 to 20 for fossil fuel usage (9). The land required to raise the feed to produce animal protein is 6–17 times greater than for soy protein (9).Thus, the conversion of plant foods to foods of animal origin is an intrinsically inefficient process (~10:1).The ratio of energy inputs to protein delivery is also qualitatively different for animal compared with plant foods. As the concentration of protein increases in plant foods, so does the efficiency. It does not change or may even decrease in animal protein sources (Figure 3) (10). High-protein plant foods such as soy beans and other legumes have greater protein delivery energy efficiency than cereals, which have a lower protein concentration. Therefore, less energy is needed to produce the same amount of protein from soy than from corn. However, very similar amounts of energy are used to produce equivalent amounts of protein from different sources of animal protein. In animal foods, the degree of protein concentration seems to decrease the efficiency ratio of energy inputs compared with protein outputs.
