WHAT DOES SUSTAINABILITY MEAN FOR DIETS AND THE FOOD SYSTEM?
Sustainability in our food system is a complex topic. It encompasses multiple domains (economic, environmental, social) and long-term time scales (generational impacts). Issues as varied as greenhouse gas (GHG) emissions, wildlife habitat, rural livelihoods, the affordability of food, nutritional quality, and animal welfare can all fall under the broader umbrella of sustainability. Further complicating sustainability is the reality that there can be tradeoffs and interrelationships across domains. For example, animal source foods in general produce more GHG per kilocalorie than plant source foods; however, animal source foods also tend to provide more of several essential nutrients in bioavailable forms per kilocalorie, such as iron, calcium, and vitamin B12.1 Finally, the multiple issues that fall under the umbrella of sustainability are subject to value judgments, cultural differences, and traditions. What is most valued by one individual may be different for another, which means that sweeping statements about one-size-fits-all dietary advice or generalized public policy recommendations are difficult to provide.
Given the complexity outlined above, what are some of the definitions of sustainable food systems and diets? The United Nations' Food and Agriculture Organization (FAO) defines a sustainable food system as “a food system that delivers food security and nutrition for all in such a way that the economic, social and environmental bases to generate food security and nutrition for future generations are not compromised.” The same organization defines sustainable diets as “those 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.”2
The bottom line is sustainability is a complex balancing act full of nuance and shades of gray. This article will highlight this complexity and provide practical advice with a food that is often in the crosshairs in healthy, sustainable diet discussions: beef. The following information on beef production, sustainability, consumption patterns, and food waste will be largely focused on the United States.
BEEF CATTLE PRODUCTION IN THE UNITED STATES
The US beef supply chain is one of the most complex of any food. Beef cattle production starts in the United States on operations called cow-calf operations, more commonly known as farms or ranches depending on the region of the country. According to the 2017 US Department of Agriculture (USDA) Census, there are more than 720 000 beef cow-calf operations in the United States, with operations in all 50 states. This makes beef the single largest segment of the US agriculture, as cow-calf operations represent 36% of US farms and ranches. Cattle and calves were the top ranked commodity in US agriculture in 2017, with $77.2 billion in sales.3
Cow-calf production is extensive, meaning that most cows in the United States are housed on pasture or rangeland and spend most of their time grazing and eating forages, such as hay. On these operations, a beef cow will have a calf ideally once per year (the gestation period of cattle is similar to humans—approximately 285 days), and the cow will nurse the calf until weaning, which typically occurs when the calf is 6 to 10 months old and weighs 450 to 700 lb. Once weaned, cattle may remain on grass and graze for another 2 to 6 months, or the cattle may enter a feedlot, while still consuming a high-forage diet (>50% of their feed intake). Cattle during this time are referred to as stockers or backgrounders, respectively. The final phase of cattle production is known as finishing, where cattle will continue to gain lean muscle, but will also add a higher proportion of fat, in particular intramuscular fat known as marbling. At the end of finishing, cattle will weigh between 1200 and 1400 lb. Most cattle in the United States (~97%) are finished in feedlots and fed a grain-based diet for approximately 4 to 6 months before slaughter; however, proportionally, approximately two-thirds of the animal's lifetime is spent outside of feedlots. A much smaller proportion of cattle will be finished on grass or by consuming a 100% forage diet (eg, hay, silage, or fermented whole plants such as alfalfa) for approximately 6 to 10 months. In addition, dairy cattle will enter the beef supply, both in terms of culled dairy cows and male dairy calves that are raised as steers just as beef breed cattle (eg, Angus, Herefords). The US veal industry is small (74.5 million lb of veal production compared with 27.2 billion lb of beef production in 2019) within the United States and concentrated in the Northeastern and Midwest United States.4,5
Most beef cattle in the United States are not in a feedlot at any given point in time. For example, on January 1, 2019, the USDA estimated that there were 14.4 million cattle in feedlots, with the remaining 82% of the US beef cattle herd located outside feedlots primarily on pasture and rangeland (Figure 1).6 The US beef cattle industry is a combination of grass-based and grain-based feed intakes, with most of cattle's lifetimes and feed consumption resulting from grass and other forages.
HOW BEEF FITS INTO A SUSTAINABLE FOOD SYSTEM
The nature of beef cattle production is central to its contributions to a sustainable food system. Most of the land and feed resources used by the US beef cattle industry are not in direct competition with human food production, meaning that most of the land used by cattle cannot be cultivated to grow crops we eat directly (eg, fruits and vegetables) and most of the feed that cattle eat is inedible to humans. Animal feed–human food competition is a key topic in sustainable food system discussions as it potentially reflects natural resource competition and can influence how many people can be nourished in total from the food system.
A multiyear survey of US cattle farmers and ranchers found that the feed resources required to produce beef are 82% human-inedible forage (eg, grass, hay), 7% byproducts or human-inedible plant leftovers (eg, dried distillers grains), and 11% grain (eg, field corn, which is different from sweet corn consumed by people).7 This translates into 2.6 kg of grain per kg of beef produced in the United States. Given the most recent year's beef production, corn yields, and corn acres harvested, corn grain harvested and fed to beef cattle in the United States was derived from approximately 8 million acres.8 This is equivalent to 10% of harvested corn acres, 2% of cropland acres, and 0.3% of the land area in the United States.9
The feed resources required to produce a pound of beef, or any animal source food product, is often of interest in sustainability assessments as a reflection of feed-food competition. Frequently cited statistics include 6 lb, 3 lb, and 2 lb of feed to make 1 lb of beef, pork, or chicken, respectively. However, this feed conversion for beef does not account for the other segments of the beef industry outside of the finishing phase (cow-calf and stocker/backgrounder) and fails to make the distinction between the diet composition consumed by these different species.
Cattle are ruminants, which means their digestive systems are uniquely evolved to use fibrous plant materials (forage) for energy and nutrients by way of microbes so that they do not have to depend on high-quality dietary sources of protein to meet their amino acid requirements. The microorganisms within cattle's specialized stomach compartments pass on to the animal's gastric stomach compartment (abomasum) and small intestine and are a source of high-quality, readily digestible protein for the animal. Similarly, the microorganisms are sources of essential vitamins such as vitamin B12, which is why ruminant products (beef, lamb, cow's milk, etc) are such excellent sources of vitamin B12 for humans.
Pigs and chickens are similar to humans in that they are monogastric animals and depend upon the dietary intake of high-quality protein to meet their daily amino acid requirements. As a result, diets fed to pigs and chickens in the United States typically include soybean meal as a high-quality protein source. Ultimately, which species is considered most efficient at converting feed into human food depends on how feed conversion efficiency is expressed (Table 1).
TABLE 1 -
Comparison of Feed Conversion Efficiency Expressed 3 Different Ways
||Dry Matter Feed Conversion, lb of Feed Dry Matter/lb of Live Weight
||Human-Edible Feed Conversion, lb of Potentially Human Edible Feed (Corn, Soy)a/lb of Live Weight
||Net Protein Contributionb (Values >1 Mean More High-Quality Protein Generated Than Used)
|US average grain-finished beef for full life cycle7
This example demonstrates how a conclusion about which animal production system is most efficient is dependent upon how the sustainability metric is expressed.
aAnimal feedstuffs such as corn grain and soybean meal could be consumed by people and thus are classified as human-edible feeds. Forages like grass and hay cannot be consumed by people and thus are classified as human-inedible feeds.
Net protein contribution is human-edible protein return * protein quality ratio (PQR). Human-edible protein return is the kilograms of human-edible crude protein in the beef, chicken, or pork divided by the corresponding kilograms of human-edible feed crude protein consumed by the cattle, chickens, or pigs. Protein quality ratio is the digestible indispensable amino acid score (DIAAS) of beef (111.6), pork (113.9), or chicken (108.2) divided by the DIAAS of the animal's diet (beef cattle, 42.2; pigs and chickens, 60.9). The diets of pigs and chickens have a higher PQR because of the inclusion of soybean meal. Net protein contribution values greater than 1 indicate more high-quality protein generated in the form of meat than the animals consume (ie, adding to the human food protein supply).12
CONTEXT ON BEEF'S GHG EMISSIONS
A quick Internet search of beef and GHG emissions will result in a wide range of statistics, and 3 types of conflation typically occur that can make understanding which statistic is the most appropriate to use confusing to a nutrition professional. First, globally relevant statistics are often conflated with US emissions; second, all emissions from livestock production are often ascribed to beef; and third, direct and life cycle emissions are often used interchangeably without explicit delineation as to what emission sources are or are not included within a percentage.
According to the US Environmental Protection Agency (EPA) GHG emissions inventory, 2% of US emissions come directly from beef cattle (methane from cattle belches, methane and nitrous oxide from managed manure which is mostly the manure in feedlots). Total direct emissions from all agricultural production, crops and livestock collectively, were 8.4% of US emissions in 2017. Agriculture, land use, land use change, and forestry combined in the United States are a net sink of CO2 equivalent (CO2e) emissions, meaning they removed 172 million metric tons of CO2e from the atmosphere in 2017.13
Globally, life cycle emissions from livestock production (emissions from feed production to consumer) are estimated to be 14.5% of GHG emissions. Global beef life cycle emissions are 6% of the world's GHG emissions.14 The disparity between these 2 percentages is the other forms of livestock agriculture accounted for in the 14.5% figure, such as poultry, pork, and dairy production. Beef cattle do represent a higher proportion of total GHG emissions from animal agriculture than monogastric animals like pigs and chickens. This is one example of a sustainability tradeoff: beef cattle production has less feed-food competition and beef cattle are able to use more nonarable land than pigs and chickens; however, because cattle are ruminant animals, they produce more methane gas (a GHG 28 times more potent at trapping heat over a 100-year timeframe than carbon dioxide) from their digestive tracts.13
In the United States, beef cattle production produces 3.7% of US GHG emissions from a life cycle perspective. This partial life cycle assessment (LCA) estimate adds in emissions from feed production (eg, emissions from soil, manure on pasture lands), fuel and electricity use, and others, to the 2% estimation from the EPA inventory, hence why an LCA GHG estimate is higher than the EPA's direct emissions from the animals and their managed manure.7 The GHG emissions produced by US beef cattle contribute only a fraction of the GHG emissions attributed to global beef production, as most cattle in the world are located outside US borders: US beef cattle production emissions are less than 0.5% of the world's GHG emissions.
Importantly, emissions from cattle and other livestock are not static, and there remain many opportunities to reduce emissions further. Both in the United States and around the world, beef production has become more efficient, and GHG emission produced per pound of beef has declined. In the United States, according to United Nations' FAO data, direct GHG emissions from beef cattle have declined 33% from 18 lb of carbon dioxide equivalents in 1975 to 12.1 lb of carbon dioxide equivalents in 2016 per pound of beef produced.15 This reduction in beef's carbon emissions is a result of a decline in the size of the US cattle herd. In 1975, the United States had 132 million beef and dairy cattle and produced 24 billion lb of beef. In 2016, the US cattle herd had shrunk to 92 million heads, but beef production was slightly higher at 25 billion lb.6 The global average carbon emission intensity of beef has declined 20% from 1975 to 2016, falling from 32 to 25.7 lb of carbon dioxide equivalents per pound of beef, respectively.15 The ability to produce more beef with fewer animals means fewer natural resources are required and less GHG emissions are produced to generate human nourishment. This improvement in efficiency was gained primarily through improvements in animal genetics, animal nutrition, and husbandry practices. Continuing improvement in these areas of beef cattle production can further reduce environmental impacts within the United States and around the world.
Research and extension and adoption of new knowledge are a continuous process that delivers on incremental improvements in reducing beef cattle production's resource use and environmental impacts. Advancements in grazing land management, animal breeding decision making enhanced by genomic information, methane inhibitors, integrated crop-livestock systems, water recycling technology, and manure composting are just a few of the examples of new technologies being deployed and tested that will further enhance the sustainability of US beef production in the years ahead. These efforts are being driven by private businesses within the beef supply chain, public entities like Land Grant Universities and the USDA, and multistakeholder groups such as the US Roundtable for Sustainable Beef.
THE SUSTAINABILITY-DIET CONNECTION
Defining a Sustainable Diet
As referenced previously, the FAO's definition of sustainable diets makes clear that many dietary patterns can be sustainable. The definition also presents the complexities involved in determining whether a dietary pattern is sustainable. One must consider many factors, including location, climate, culture, economics, nutritional adequacy, and available natural and human resources. A sustainable diet in one part of the world may not be in another part of the world or even a given country.
People, Planet, and Profit Considerations
In considering the defining variables of a sustainable diet, the triple bottom line is an accounting framework that evaluates its impact on people, planet, and profit.16,17 This framework can then be used to determine the impact of a particular dietary pattern and ascertain if that dietary pattern meets the criteria for a sustainable diet.
Evaluating Impact on People
As shown in the 2015–2020 Dietary Guidelines for Americans, there are many dietary patterns that are nutritionally adequate, providing enough calories and essential nutrients.18 Nutritional adequacy is fundamental to healthy, sustainable diets. Human biology allows for flexibility with food choice regarding meeting nutrient requirements and achieving optimal diets, which is especially fortunate because lifestyle, culture, tradition, and values are often more powerful daily drivers of food choice than the quest for adequate or optimal nutrient intake.
There are many cultural factors that will influence food intakes, including ethnicity, race, and religion. The term “food culture” historically has referred to where people live and the traditional dietary patterns of that region or area (eg, Mediterranean food culture). More recently, research has focused on the impact of dietary patterns on an individual's food culture.
Costa and colleagues19 looked at how young women choosing to eat a vegan diet do not consider it a diet to follow but rather a lifestyle to live. This finding starts to blur the lines between considerations of culture and lifestyle. Nutrition practitioners need to not only understand the nutrition implications of various dietary patterns but also the lifestyle implications. When a dietary pattern becomes part of a person's identity rather than just a way of eating, recommendations to alter the diet can have a profound impact on a person's sense of self, well-being, and confidence.
Other factors to consider when evaluating a dietary pattern include lifestyle. A sustainable dietary pattern for a woman with 3 young children who works 2 jobs, lives in an urban food desert, relies on public transportation, and is at risk of food insecurity is very different from that of an educated, upper middle class woman with no children who works at home, lives in the suburbs, orders home meal kits, joyfully cooks each evening during the week, and dines out with friends and family on the weekend.
Over the past 10 years, much as been published on the negative impacts of “food elitism,” the practice of making food, beverage, or diet recommendations that require more money and/or more time like recommending fresh fruit and vegetables over processed forms including frozen or canned. Lawrence and colleagues20 write of marketers that target LOHAS (Lifestyles of Health and Sustainability) consumers who “have a strong interest in health, fitness, personal development, and social justice, and put a high value on sustainability and environmental protection.” These marketers promise higher quality and charge premium prices. Although their marketing is targeted, their messages are often far reaching, imparting feelings of fear or failure for consumers who believe their messaging but cannot afford their prices or do not have access to their products.
Huang and colleagues21 reported the negative impact of organic marketing on low-income shoppers and their fruit and vegetable purchases. Messaging about production methods (eg, organic and conventional production) and pesticide residues in 12 fruits and vegetables highlighted by the Environmental Working Group “Dirty Dozen” report resulted in shoppers reporting they were less likely to buy any fruits and vegetables. If nutrition professionals believe fruits and vegetables are an important part of sustainable diets, efforts must be made to communicate in ways to motivate people to buy and consume more fruits and vegetables versus less. The same applies to messages about beef production. Production information that creates a negative perception of a food's nutritional value is not helpful; nutrition professionals should strive to provide information about the role of beef in healthful diets that allow patients and clients to make informed not fear-based choices.
Evaluating Impact on the Planet
Dietary choices may have an impact on soil, air, and water as well as GHG emissions and their potential impact on climate change. Dietary choices also have an impact on other natural resources like fossil fuel use for production, processing, distribution, and storage. When considering the impact of a specific dietary pattern or individual food, it is critically important to evaluate LCA data and not focus solely on individual measurements or metrics. Many refer to an LCA analysis as a “cradle-to-grave” assessment from the birth or beginning of a food product to its final use or when it becomes waste. According to Satpute and colleagues,22 “LCA enables the estimation of the cumulative environmental impacts resulting from all stages in the product life cycle.” Readers interested in learning more about how LCAs apply to foods can read Cucurachi and colleagues'23 “Life Cycle Assessment of Food Systems” primer and Halpern and colleagues'24 opinion piece “Putting All Foods on the Same Table: Achieving Sustainable Food Systems Requires Full Accounting.”
Although it is tempting to compare foods based on a single metric like water use, doing so does not tell the full story of environmental impact. Likewise, sharing data on global averages is not a fair and balanced use of the data. For example, about 45% of GHG emissions in Ethiopia come from enteric fermentation from livestock.25 Meanwhile, in the United States, GHG emission from livestock is 4%.13 Yet, when GHG data are reported, many will report a global average that makes the impact of US livestock production look worse than it is.26 Perhaps one of the biggest challenges facing nutrition professionals today is the fact that nutrition science is a relatively new field and we have much to learn. Coupled with that, our colleagues in environmental science work in an even younger discipline with less than 20 years of robust peer-reviewed literature. As a result, we need to be mindful that we currently know much more about healthful dietary patterns than we do about the environmental impact of our food choices.
Evaluating Impact on Profits
Farm and ranch families comprise less than 2% of the US population. Meanwhile, as a result of the productivity and efficiency of these US farmers and ranchers, people in the United States have access to an abundant, affordable, and safe food supply.27 As with any business operation, a farmer's or a rancher's ability to make a profit is part of his/her sustainability story; no farm or ranch can be environmentally sustainable without also being financially sustainable. It is therefore critically important for farmers and ranchers to be able to operate in ways that maximize their ability to produce a profit while protecting natural resources.
In the United States, nearly two-thirds of land for agriculture cannot be used to grow crops.28 The soil quality may be too poor, topsoil depth too shallow, land too rocky, slope too steep, or trees too dense to successfully grow crops. Farmers and ranchers with this type of pasture, range, or forestland can use it to produce food by grazing livestock on it. Proceeds from the sale of livestock contribute to the overall economic viability of the farming or ranching operation with marginal land that cannot support crops.
So how does the financial sustainability of farmers and ranchers affect consumers? When US farmers and ranchers are productive, efficient, and financially stable, they can continue to produce food for the 98% of the population not involved in agriculture. If we lose farmers and ranchers, we lose food security, relying on producers in other parts of the world to feed us, which can impact food quality, availability, and cost.
TRANSLATING THE EVIDENCE
The Role of Animal Protein in Sustainable Diets
If we go back to the FAO definition of sustainable diets and evaluate what “nutritionally adequate” means, we must look at both macronutrient and micronutrient needs. The 2015-2020 Dietary Guidelines included a Healthy Vegetarian Eating Pattern showing that we can get adequate protein from a variety of plant-based foods as well as dairy products and eggs.18 But there are certain micronutrients like choline, heme iron, zinc, and the essential fatty acid EPA that are easier to consume in adequate amounts when animal-based foods are included in healthful dietary patterns. According to the USDA National Nutrient Database, the top sources of each of these nutrients are animal-based products like eggs (choline), oysters (iron), beef (zinc), and salmon (EPA).29
Beef is an example of a nutrient-rich food that can contribute significant nutrients with relatively few calories. According to National Health and Nutrition Examination Survey data, individuals aged 19 to 50 years consume 1.7 oz of beef per day; adults older than 50 years consume slightly less beef per day (1.3 oz).30 In this same analysis, lean beef contributed less than 5% total fat and less than 4% total saturated fat. A separate analysis shows that beef contributes approximately 5% of total calories to Americans' diets while contributing more than 5% of these essential nutrients: potassium (6.1%), phosphorus (7.3%), iron (8%), vitamin B6 (9.2%), niacin (9.9%), protein (15.2%), zinc (23.1%), and vitamin B12 (25%).31 Teaching patients and clients how to choose lean beef helps them obtain optimal protein and micronutrient benefits while limiting total fat, saturated fat, and calories from beef. The USDA defines “lean” beef as 100 g (3.5 oz) of uncooked beef with less than 10 g of fat, 4.5 g or less of saturated fat, and less than 95 mg of cholesterol.32 Counseling patients and clients to choose nutrient-rich foods like lean beef is a powerful role nutrition professionals can play when it comes to helping individuals and populations overcome nutrient deficiencies.
In addition to nutrient adequacy, we must also address and respect food preferences and cultural food patterns. Many people like the taste, texture, mouthfeel, aroma, and other sensory properties of animal-based foods like milk, cheese, chicken, pork, and beef. All these foods can be included in healthful, balanced dietary patterns that are also sustainable.
The Mediterranean dietary pattern is an example of a cultural food pattern that has been widely adopted because of both flavor and health benefits. A recent study by O'Connor and colleagues33 demonstrated the benefits of including lean beef in a Mediterranean-style dietary pattern. In this randomized, controlled feeding trial with 41 overweight or obese adult subjects, participants in the red-meat group who consumed 500 g (18 oz) of lean, unprocessed beef or pork each week had greater reductions in total and low-density lipoprotein cholesterol compared with participants in the control group, who ate 200 g (7 oz) of lean, unprocessed beef or pork each week along with other protein-rich foods. Patients who enjoy lean beef can be encouraged to eat it as part of healthful dietary pattern, like the Mediterranean diet, that includes other nutrient-rich foods more commonly associated with healthy, sustainable diets.
The Need to Reduce Food Waste
Food waste is one of the biggest opportunities to address when it comes to promoting sustainable diets. In the United States, we currently waste 30% to 40% of available food.34 Food waste occurs throughout our food system, starting in agriculture (16%) and food processing (<2%), moving to losses in restaurants and retail (40%), and finally to in-home losses (43%).35 Meat, poultry, and fish are the top wasted foods in the home based on value.35,36 Teaching patients and clients how to properly store, handle, freeze and thaw, cook, and/or reheat these foods can reduce food waste in the home.
The environmental impact of food waste ranges from the extensive losses of natural resources that go into producing food (eg, land and water for crops; land, feed, water for animals; fossil fuels for machinery; etc) to the production of methane as wasted food in landfills decomposes through the work of methane-producing microorganisms. Municipal solid waste landfills are the third largest emitter of methane in the United States.37 Reducing the amount of wasted food that goes into landfills is an important and effective strategy for enhancing food security while reducing GHG emissions.
PRACTICAL APPLICATION OF THE SCIENCE
The Role of the Nutrition Professional
Although the issue of sustainability is undoubtedly complex, the role of the nutrition professional in promoting sustainable diets is clear. Science- and evidence-based information that motivates our patients and clients to adopt healthful eating patterns should be used as the foundation of our recommendations, while recognizing and respecting that there are different ways for our patients and clients to achieve healthy, sustainable dietary patterns. There are environmental, social, financial, and health benefits to including nutrient dense, animal-based foods in a healthful dietary pattern; further, the inclusion of these foods may improve adherence to a healthful dietary pattern if our patients and clients enjoy them. Finally, beef can fit into a sustainable food system to deliver good nutrition because it is responsibly produced, affordable, accessible, acceptable, and nutrient-rich. With good judgment and good science applied to animal husbandry, it is possible to feed people beef in a sustainable way.
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