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Sustainable diets are defined as "those diets with low environmental impacts that contribute to food and nutritional security and to healthy lives for present and future generations. Sustainable diets are protective and respectful of biodiversity and ecosystems, culturally acceptable, accessible, economically fair and affordable, are nutritionally adequate, safe, and healthy, and optimize natural and human resources." These diets attempt to address undernourishment, nutrient deficiencies and obesity and covers ecological phenomena such as climate change, loss of biodiversity and land degradation.
Sustainable diets frequently seek to reduce the environmental impact of the whole contributing food system, from production practices, to distribution and other economic or systems considerations (such as food waste). However, most sustainable diets include reducing consumption of meat, dairy and eggs, because of the broad negative environmental impact of these industries.
As a theme, it also covers the study of eating patterns that take into account the impact that food consumption has on planetary resources and the health of humans and promotes the needs of the environment, society, and the economy. This growing body of research is recognized by a variety of international bodies such as the United Nations Food and Agriculture Organization (FAO) and the World Health Organization (WHO).
The first description of a sustainable diet was in the 1986 paper by Gussow and Clancy. They describe sustainable diets as "food choices that support life and health within natural system limits into the foreseeable future." In 2010, the FAO and Bioversity International defined a sustainable diet 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.
The FAO further outlines the aims of sustainable diet practice as to achieve optimal growth and development as well as support for physical, mental, and functional wellbeing, while preventing malnutrition and promoting biodiversity and planetary health. Subsequent literature tries to turn that interpretable concept into "operationalizable" concept for creating a sustainable food system.
Motivations and awareness
Between 2010 and 2014 an increase in the awareness of sustainable benefits of decreasing meat consumption was observed. A longitudinal study taking place over the span of these four years attributed perceived environmental impact to approximately 41% of individual's explanatory reasoning for consuming less meat.
An increase in knowledge of environmental impact was observed. This means, when individuals were asked to comment on whether or not meat consumption is linked to climate change, the number of people responding positively increased. Researchers justified this increase as part of a “halo” effect. Meaning, due to an increase in health consciousness and economic efficiency for individuals as well as individuals desire to eat more healthily they also positively increased their evaluation of environmental impacts.
Food consumptions decisions have been found to hinge on health, naturalness, price, and sociability. All of these factors are associated with reducing meat consumption and increased willingness to follow a plant based diet besides sociability, which only has been connected to reduced meat consumption. The aspect of sociability and the social setting also pushes individuals to want to maintain the status quo in their consumption habits rather than convert to a more sustainable diet. Because the positive environmental impact also aligns with individual's health goals and concerns as well as limit cost effectively they more positively evaluate and care for the environmental impact.
Over the span of the longitudinal study, awareness of the link between meat consumption and environmental impact increased as well as meat consumption and health outcomes. Emotion-focused coping may provide one explanation for the increase in environmental awareness that eating less meat is good for sustainability. This concept states that defense mechanisms such as denial and rationalization may be mental strategies used to decrease negative emotions. As individuals begin to partake in more environmentally positive behaviors, regardless of motivation, this may alleviate their need for denial and rationalization and lead to their comprehension and understanding that eating more healthily is also more environmentally sustainable.
Motivation and Values
Motivation is defined as what individuals choose to do, how intensely they choose to do it, and the amount of time the behavior is maintained. This definition is not specific to environmental choices and food consumption but can be easily utilized in this setting due to its generalizable nature. This as well as the types of values held may play crucial roles in individuals environmental behavior and food choices. There are three main value types that are important for the current topic; egoistic, altruistic, and biospheric.
Egoistic values are those that concern individuals because of a direct personal impact. Altruistic values are those that concern individuals because of their relevance to others. Biospheric values are those that concern individuals’ due to their impact on ecological systems, nonhuman animals, and plants. Individuals justification of choices, behaviors, and actions regarding their food choice and its environmental impact are due to one or more of these value sets. Choices affected and caused by the halo effect are due primarily to egoistic values and then extrapolated to encompass one or both of the other value types; the choice was originally personally motivated but happened to bleed over into a positive outcome aligning with a less self-focused intention.
Everyday there are an exorbitant amount of choices that individuals must make. It would be impossible to stop and thoroughly consider each decision as well as all subsequent options and thus heuristics have been created. In regards to psychology, a heuristic is a cognitive shortcut employed to make quick decisions without using excess amounts of cognitive resources. Heuristics are used daily and often in food choice. Individuals know what they like to eat and often make food choices mindlessly. That is, food choices are not always a reflection of motivation or values and do not reflect individual's potential environmental intentions or lack thereof but are instead choices not mindfully made.
The FAO and WHO have outlined 16 components of a sustainable, healthy diet. The outline divides the components into sections regarding health aspects, environmental aspects, and sociocultural aspects. Each component is also in line with current United Nations Sustainable Development Goals (SDG).
According to the United Nations, a sustainable, healthy diet begins with breast feeding. For children and adults, it includes a wide variety of minimally processed foods that are balanced across food groups. The sustainable diet is primarily plant-based, relying heavily on whole grains, legumes, fruits, and vegetables. The sustainable diet is also supplemented by moderate amounts of eggs, dairy, poultry and fish, and includes minimal red meat. The sustainable diet is also meant to be moderate in proportion, with all dietary needs being satisfied but not heavily exceeded. Finally, a healthy sustainable diet also includes safe and clean drinking water.
In order to qualify as a sustainable diet using UN guidelines, a diet must keep greenhouse gas emissions, use of fertilizers, and pollution within established sustainability targets. The diet must also reduce the risk of non-communicable diseases and promote general wellbeing. Additionally, foods produced in line with a sustainable diet should minimize antibiotic and plastic use.
An ideal sustainable diet also takes into account local culture and culinary practices in a given region, including emphasis on locally-sourced food products and regional food knowledge. The diet must also be accessible and affordable to all, and not encourage gender-related burdens of labor.  This is a crucial part of claiming a sustainable diet. Many consumers do not realize the impacts of producing certain products have on the surrounding cultures. Sustainability means being ethically sourced. A main aspect of sociocultural sustainability is the focus on managing and identifying impacts on these cultures, businesses that produce the product and the employees. 
Diets described as sustainable
Sustainable diets are typically associated with low-carbon diets, which are structured to reduce the impact of global warming. The most important examples of this type of diets are Plant-based diet. Other approaches also focus on broader environmental factors, as well as social and economic challenges. For example, approaches focused on diets tied to specific regions include the Mediterranean diet, a plant-based diet that is rich in fruits, vegetables, whole-grains, legumes, and to a smaller extent fish, among the sustainable ones.
It is often thought that food-locality is an important component for a diet to be environmentally sustainable. However, a very comprehensive study that gathered data across more than 38k farms showed recently that this is not the case, as the carbon and pollutant footprints due to the transport of food are almost always negligible compared with the other sources characteristic of food production. The only exception to this rule are avio-transported food items, which are niche products (e.g., most tropical fruits and nuts do not fly).
A 2020 study found that the climate change mitigation effects of shifting worldwide food production and consumption to plant-based diets, which are mainly composed of foods that require only a small fraction of the land and CO2 emissions required for meat and dairy, could offset CO2 emissions equal to those of past 9 to 16 years of fossil fuel emissions in nations that they grouped into 4 types. The researchers also provided a map of approximate regional opportunities.
Sustainable diets and gender
Women are more likely to buy products labeled as being green, environmentally friendly, and sustainable than men. There is a stereotype of green products being made for women thus creating the illusion that sustainable behavior is inherently an feminine practice.
This stereotype of sustainable behavior being inherently feminine has the potential to be overridden through the packaging of green products. If the packaging on the product reaffirms men's masculinity, that mitigates the threat men feel towards their masculinity and purchasing the product is not off-putting because of perceived femininity. Another way the stereotype may be overridden is having a community surrounding the green or sustainable behaviors that is predominantly male or has a masculinity-reaffirming undertone. An example of such a group is gourmets, persons who participate in gastronomy. They are mostly men and their behaviors are of a sustainable nature.
“Less but Better” practice of meat consumption
The phrase “less but better” refers to the decrease in overall amount of meat while increasing the overall quality of meat consumed. Quality, in this case, refers to the sustainable and responsible manner in which the livestock are raised. This means eating less meat that both tastes better and is more sustainably raised. Another similar phrase is “less but more varied” referring to less meat protein being consumed while simultaneously including more varied forms of protein such as plant based proteins. This could be in the form of a single meal not containing meat or meat-‘less’ day in which an entire day's worth of food lacks meat in content. Both of these phrases have been shown to affect consumer choices. When 1,083 consumers were given information regarding their current eating practices and the suggestions for potential improvements were given through the implementation of these phrases it was discovered that both of these phrases influence overlapping but slightly different consumer bases. Meaning that both phrases were effective when implemented but not with all consumers. Of the consumers that were influenced by the phrases each phrase was effective for slightly different varieties of consumers.
How the phrase of “less but better” effects consumers is ingrained in the consumer choice of whether or not to eat meat. Many individuals do not want to harm animals or see them suffer but choose to consume diets in which these are the outcomes for animals. This situation has been dubbed “the meat paradox”. Individuals cope with this cognitive dissonance often through ignorance (ignoring the known realities of their food source) or explanations loosely tied to taste. The cognitive dissonance intensifies if mind or human-like qualities of animals are explicitly mentioned.
Less but better is a concept also commonly used by gourmets. Gourmets are taste and quality oriented consumers. Gourmets are individuals who partake in gastronomy, which in simple terms is the practice of choosing, creating, and enjoying high quality food. This practice is typically, but not exclusively, dominated by men. This type of consumer has a high regard for the quality of their food and ingredients. They typically research and strive to use what is locally produced and in season. Meat that originates from grazing livestock rather than industrial farming techniques where livestock are fed unnatural diets is typically if not always preferred by gourmet consumers.
The regulations gourmet's place on themselves are inherently sustainable although they are not purposefully intended to be this way. Gourmets prefer to work with produce that is in season and locally sourced. They enjoy cooking and creating meals that only rely on plants alone due to the challenging nature of creating such meals to their standards. If they do choose to indulge and include meat in their dishes they do so in small, high quality portions. Adhering to these standards are not only creating the level of quality strived for by gourmets but also aligning with sustainability as a side effect.
Reactions and policy
Most responses to sustainable diets and create dietary guidelines for sustainable diets is focused in the work of NGOs and researchers. Governments have been slow to adopt "sustainable diet" guidelines, with only a few publishing recommendations. Some industries, such as the meat alternative industry, have embraced these recommendations, while the Meat industry is actively lobbying against it. More generally, industrial food companies have not adopted "sustainable diet" as part of their Corporate sustainability strategies.
Sustainability of dietary recommendations
Dietary recommendations are available on the packaging of nearly all food items sold from grocery stores. Environmental information, such as green-house gas emissions though, cannot be commonly found on the packaging of food items sold at nearly any location. A shift towards more plant-based diets can generate substantial public health gains. This is increasingly true if the diets contain foods such as nuts, fruits, vegetables, and legumes due to their health protective qualities and lack of harmful factors such as transfats. The human body is also more efficient in transforming these food sources into calories and nutrients, adding to their health benefits. Countries such as the Netherlands and Sweden have established guidelines of sustainable diets for their citizens. The United States of America has not officially established any such guidelines.
Healthier diets are associated with a reduction in greenhouse gas emissions. In fact, as compared with a typical American diet, a change to a healthy diet has the potential to reduce emissions up to fifteen percent. Even greater gains in emission reduction have the potential to occur if individuals changed their diet with the purpose of sustainability. This would result in an emission reduction of up to twenty-seven percent. Neither of these dietary changes require individuals to completely cut out meat from their diets; although, a reduction in meat consumption is commonly required for individuals to meet dietary recommendations. In America, it is common for individuals to over consume meat and protein while lacking nutrients in the other remaining categories. The largest change required of individuals is an adjustment to the amounts of nutrients they currently consume such that they meet the current health recommendations in all of the nutrient categories 
Germany is another country that currently lacks official guidelines for a sustainable diet. Research conducted in 2014 by Meier, Christen, Semier, Jahreis, Voget-Kleschin, Schrode, and Artmann analyzed the country's current lack of sustainable diets and how land usage can be adjusted to balance internally created with imported goods. The research also showed the potential for a reversal in the import/export pattern of the country such that Germany may export more goods than they import currently.
Challenges of food consumption and environmental impact
Taste, health, and sustainability are three seemingly separate factors inherently linked by a common thread; environmental sustainability. To have a healthy diet is to have one with many sustainably qualities. Some may argue that sustainable diets are not feasible because they require meat to be cut out or that they will have to eat worse tasting food as a consequence. Both of these misconceptions are untrue, in fact, there are groups of individuals who place the highest value on the taste and quality of their food over other aspects and have consequently created an incredibly sustainable diet. There are a variety of motivations, values, and influences that effect individuals dietary choices  An extensive overview of what has been discussed and more will be provided below.
There is a current lack of awareness between meat consumption and climate change such that many individuals do not perceive there to be a link between the two concepts. Even when the two concepts are recognized as being connected in some way, individuals are highly skeptical of the degree of the connection. Many use their skepticism to convince themselves that the environmental impact is not worth recognition in regards to a behavior change.
People are reluctant to engage with the idea that their personal meat consumption has any role in the global context of climate change. They believe that their individual contribution will have little to no effect on the current state of affairs. Even believing that changing their individual behavior would, to a minimal degree, help alleviate the effects of climate change is highly contentious. Meaning, that people view their own decrease in meat consumption as having little to no effect on climate change overall. With this belief being widely held, it may not be surprising that research has also shown reluctance and resistance to the decrease of meat consumption by individuals. Those who desire to act on climate change in a positive manner view behavior change outside of food consumption as more desirable and an action they are more willing to participate in. Reasons for this resistance include; the taste of meat is a pleasurable one, individuals perceive themselves as taking other steps towards sustainability in other ways and thus do not feel obligated to indulge in this act, and are skeptical to meat production's link to climate change.
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