Protein: we need quality, not just quantity


Getting enough protein in our diets is essential for adequate nutrition. What is less well known is that protein represents a group of nutrients, the amino acids, each of which needs to be consumed in sufficient amounts. Here, we look at how we digest protein, the importance of amino acids, and show that protein quality, not just quantity, is vital.

Protein, alongside carbohydrates and fat, is one of the dietary macronutrients found on the nutrition label of all commercially-produced food. The recommended daily intake (RDI) for protein on these labels varies between authorities, but is usually around 50 g. This allows food companies to easily calculate and display on packaging what percentage of your protein RDI is supplied by their product.

But what is meant by ‘protein’ on these labels? And where do these RDIs come from?

Protein and amino acids

Proteins are a group of molecules essential to all life, distinguishable from carbohydrates and fats by containing nitrogen. The use of proteins in our bodies is broad: they form our tendons and ligaments as collagen, break down our food as digestive enzymes, and protect from infection as antibodies, among many other roles.

Every protein is composed of a string of smaller molecules, amino acids, folded into a functional shape. The amino acids in the string and the folded shape of the protein are specific to the function of that protein.

When we discuss protein as a dietary macronutrient, we are really referring to the supply of amino acids in the foods we eat, rather than the protein per se. The protein content seen on food packaging should really be seen as the sum of the amounts of each amino acid in the food.

Protein digestion and use

Protein is present in the majority of foods we eat. The amount and type of protein varies depending on the food, but all are subjected to the same digestive processes once eaten.

Protein digestion begins in the stomach. The body produces the enzyme pepsin, which starts the breakdown of proteins with the help of the stomach’s acidic conditions. Digestion continues in the small intestine, with the enzymes trypsin and chymotrypsin continuing the breakdown of proteins to individual or very short strings of amino acids (dipeptides and tripeptides).

These small molecules, rather than the original proteins, are absorbed by the intestine and transported around the body in the bloodstream. Once absorbed, amino acids are used to construct the many proteins needed by the body.

Consuming adequate protein in the diet is essential. Our bodies do not store protein in the way we can store fat or carbohydrates. Instead, there is a constant cycling of protein construction, breakdown and excretion. This protein turnover cycle leads to around 250 grams of new protein being produced each day, either using recycled amino acids from body protein breakdown, or from the amino acids derived from newly digested dietary protein. If dietary protein is lacking, this can lead to an overall depletion of body protein over time.

The importance of each amino acid

The most common way of calculating protein RDI is by bodyweight. For example, a frequently heard recommendation is that you should eat 0.8 g of protein each day for each kg of bodyweight. Thus, a 75 kg man should consume 0.8 x 75 = 60 g of protein each day. However, there is a lack of consensus around the value of 0.8 g, with many arguing that intake should be at least 1 g, particularly for athletes and older adults.

This calculation around protein RDI hides the more specific amino acid requirements of the body. There are 20 common amino acids, 9 of which are essential. Essential means that the body cannot effectively make these amino acids itself, so must obtain them from the diet.

There are RDIs for each essential amino acid, based on the amount required for body protein production. However, these RDIs are not displayed on food products, as this would be difficult to calculate for each food and make understanding nutrition labels more difficult. Instead, the protein RDI approximates what is needed based on the amino acid content of an average diet. This approximation was designed for a population that consumes a diverse diet over time. It is less fitting for day-to-day protein consumption of the individual, particularly those who consume only a limited range of protein sources. As an individual, it’s important you obtain enough of each essential amino acid each day.

What happens if we don’t get enough of a certain amino acid?

The result of deficiency in amino acids is best explained through an analogy.

Imagine you are assembling toy cars. The process involves painting the body of the car green, and then putting on the wheels. You have a box of car bodies, a pot of green paint, and a box of wheels.

As you are assembling these cars, you come to a point where you still have car bodies and wheels, but you have run out of green paint. However, with a little more effort, you can make more green paint by mixing some blue and yellow paint you have. With this newly made green paint, the assembly process can continue.

However, if you come to a point where you have car bodies and paint, but have run out of wheels, you cannot continue to assemble the cars. No matter how much of the other two components you have, the wheels are essential, so car assembly must stop until you have more wheels.

The construction of the toy cars from components is analogous to the construction of a protein in the body from individual amino acids. In the assembly of a protein, several different amino acids are required. Like the green paint, if the body runs out of a non-essential amino acid, then it can produce more from other amino acids, although less efficiently. However, if the body runs out of an essential amino acid (those that must be derived from the diet), protein synthesis is halted – much like running out of wheels in the toy car assembly.

If you do not obtain sufficient essential amino acids from your diet, synthesis of necessary proteins can be halted. The wheels in the toy car analogy are the ‘first limiting’ component in car assembly. In humans, it is often the amino acid lysine that is the first limiting amino acid to protein synthesis. This is because lysine is required in a large number of proteins and is not always readily available from the diet. A person can be protein deficient by being deficient in just one essential amino acid, regardless of the amount of the other amino acids they consume. And since the body is unable to store protein, an excess of unused amino acids consumed will be wasted by the body when it cannot immediately use them. Getting enough of each essential amino acid is required for optimal health.

How do I ensure I get enough of each amino acid?

Different foods contain different distributions of amino acids. For example, chickpeas are higher in lysine than oats, but the reverse is true for the amino acid cysteine. Plant foods are more often limited in certain essential amino acids than animal foods, due to the similar proteins required by animals and our own bodies. If plant-sourced foods are your main source of protein, it is important to understand their amino acid profile. Plant foods with complementary amino acid profiles can be consumed together to make up for their individual deficiencies.

Another important consideration is amino acid bioavailability; the percentage of the total amino acid that is available to the body from different food protein sources. The efficiency of the protein digestion process varies depending on the structure of the protein consumed and the food matrix proteins are contained in. Extensive research has been performed on the bioavailability of each amino acid in human foods. The table below gives a summary of bioavailability values for some selected foods.

FoodAmino acid bioavailability
(% of total consumption that is absorbed)
Roasted beef94 – 99  
Fish81 – 94
Cooked kidney beans64 – 100
Oats70 – 88
Potatoes47 – 66
Rice75 – 99
Skim milk78 – 97
Cooked soyabeans71 – 90

Bioavailability of amino acids can vary widely between foods. Therefore, it is useful to have a score for each food reflective of the overall amino acid availability, commonly referred to as protein quality. The DIAAS score (Digestible Indispensable Amino Acid Score) is recommended by the UN Food and Agriculture Organisation for this purpose. The digestibility of each essential amino acid in a food is calculated and compared to a reference protein, and the DIAAS is the lowest of these calculated values. The score is thus reflective of the digestibility of the most limiting essential amino acids in the food.

A DIAAS score of 100 or more indicates excellent protein quality, with high digestibility of all the essential amino acids. Scores between 75 and 100 are considered good sources of protein, but consuming complementary proteins would improve their profile. Scores below 75 are of lower quality. Some example foods with their DIAAS are given below.

FoodDIAASLimiting amino acid(s)
Beef (roasted)99Leucine and Valine
Pea protein concentrate82Methionine and Cysteine
Rice (cooked)60Lysine
Skim milk powder105Methionine and Cysteine
Soya protein isolate84Methionine and Cysteine
Wheat45Lysine

Generally, animal-sourced foods have higher DIAAS scores than plant-sourced foods. This means that the profile of amino acids is better suited to human digestion and to fulfilling our needs for protein synthesis.

At a global scale, producing enough of each amino acid is critical to the ability of the food system to meet nutrient needs. When considering possible future scenarios, the DELTA Model predicts the supply and bioavailability of essential amino acids, as well as total protein.

Take home message

The single macronutrient protein consists of a group of essential nutrients: the amino acids. These molecules are what is needed in our diet to construct the diverse body proteins, essential to bodily function, health and life.

Getting enough protein in your diet is not just about reaching the protein RDI. Instead, you need to reach the RDI for each essential amino acid. This is most easily achieved by eating high-quality protein, or combinations of protein sources with complementary amino acid contents.


Glossary

References for DIAAS values: 1, 2, 3, 4

Green car photo by MW on Pixabay. All other photos courtesy of the Riddet Institute.

Plant-based beverages are not suitable as milk replacements for young children

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The North American Society for Paediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN) has released a nutritional position paper highlighting the deleterious effects of using plant-based alternatives to milk on infant development and health.

There are many of beverage choices available to Western consumers. These include plant-based products that are positioned as alternatives to milk. Influenced by trends such as ‘plant-based’ or ‘animal free’ and with perceived health benefits associated with the name ingredient, sales of these products have seen rapid growth.

The consumption of plant-based beverages is a matter of consumer choice and preference, appropriate in a diet that contains a balance of nutrients. However, problems arise when they are used as a replacement for dairy in cases where milk is the primary source of nutrition: for infants and young children. 

By association and with the use of dairy terms, plant-based beverages leverage the nutritional credentials of milk. This leads consumers to believe they are getting (or providing for their children) a nutritional equivalent to milk, but in a healthier way, or with a lower carbon footprint, due to the perceived halo of plant-based products. However, this is often not the case. Many plant-based alternatives fall well short of dairy nutrient content, without considering differences in the bioavailability of nutrients between plant and animal sources.  

The paper puts emphasis on protein, which is particularly important in the growth of young children.  Due to a combination of low protein content and poor protein quality, one serve of almond or rice beverage may provide only 2% or 8% of the dietary protein of an equal sized serve of cows’ milk, respectively. The paper also recommends bioavailability studies for products that have been fortified to match other nutritional characteristics of milk (e.g. calcium). 

The paper makes clear the need for consumer education to ensure that children are given the right foods for their nutrient needs. 

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Glossary

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Microbiomes and Sustainable Nutrition


Did you know that around 10% of your daily energy intake is supplied by intestinal microbes? Or that many plants and animals that we rely on for food are dependent on microbes for their survival? Although the connections between the microscopic world and the global scale of sustainable nutrition are not obvious, microbes play a significant role in the way our food is produced, processed and digested.

The term microbiome refers to a collection of microbes in a certain location. For example, the human gut microbiome consists of the microbial population living in our intestinal tract, which is receiving increasing attention as we recognise its importance in human health.

Microbiomes exist in diverse locations, many of which form part of the global food system. The role of these microbiomes in delivering sustainable nutrition for the global population is increasingly clear.

Cereal crops are a staple food source for the global population, providing predominantly energy and protein. These crops rely on soil nutrients, such as nitrogen, to grow and produce the protein we then consume. Often these nutrients are applied to cropland as fertiliser, produced either industrially or from animal sources. Management of fertiliser application is essential to avoid environmental damage caused by excess nutrients in soils and waterways.

Nitrogen can also be captured directly from the air by soil and root microbiomes, and microbes associated with roots can increase the availability of micronutrients to the plant. These microbes also increase the resistance of crops to soil pathogens. Moreover, soil microbes play a role in reducing soil erosion by producing products that bind the soil together. Current soil microbiome research is tackling the problem of reduced crop yields due to microbiome depletion and working to understand how the beneficial impacts of soil microbes can be harnessed. Learn more

In addition to plant-sourced food products, microbiomes are essential in the production of animal-sourced foods. An example of this is the rumen microbiome. Much of the forage consumed by ruminants cannot be digested by the animal’s own digestive enzymes; instead, the action of rumen microbes converts resistant plant matter, such as cellulose, to nutrients that can be absorbed by the animal’s digestive tract. These microbial products form the majority of energy intake for many domesticated ruminants. The action of the rumen microbiome is thus an important step in converting inedible plant material into animal-sourced food products in our own diet.

Rumen microbiome research currently has a strong focus on minimising the production of methane, a greenhouse gas and by-product of digesting plant material, by the rumen microbiome. This research is unpacking what causes certain microbiomes to produce less methane than others, and what the impact of different animal feeds is on methane production. Learn more

Continuing along the food supply chain, microbes are responsible for the production of common fermented foods. Fermented foods include cheeses, yoghurts, kimchi, sourdough and fermented meats, and are produced via the introduction of microbial populations to the raw food material. Apart from changing the taste, texture and appearance of these foods, the fermentation process enables perishable foods to be stored for longer periods, which can reduce food waste. The nutritional value of fermented foods is also enhanced in many cases. For example, the fermentation of cabbage to sauerkraut results in vitamin B12 synthesis, a nutrient not available in unfermented cabbage. There is also the probiotic capacity of fermented foods: their consumption can introduce beneficial bacteria to the human gut microbiome. Learn more

Microbiomes continue to play a role in the food system even after food is eaten. Although there are microbiomes in different sections of the human digestive system, the gut microbiome is intensively studied for its impacts on human nutrition and health. The make-up of our microbiome is in part determined by our diet, which forms the major food source for intestinal microbes. Just as our own ten trillion human cells require the nutrients we eat to carry out their function, so too do our equally numerous microbial cells. Current research is demonstrating increasing links between gut microbiome composition and various outcomes for human nutrition and health. This includes links to energy and nutrient yield from the diet, roles in intestinal disease and even impacts on brain function and mood. It is now recognised that we cannot have a full appreciation of human nutritional health without consideration of the gut microbiome. Learn more

A sustainable food system is one that ensures food security and nutrition for all, without compromising the future of the economic, social and environmental bases that the system depends on. Microbiomes are a critical element of a sustainable food system. Soil microbiomes enable and enhance crop growth, while playing a protective role in minimising the environmental damage of farming. Animal microbiomes are essential for the conversion of inedible plant material to animal-sourced foods, essential for food security in many developing parts of the world. Fermented foods are an integral constituent of the diet in many cultures and provide a means of preserving perishable foods, as well as adding nutritional and financial value. Finally, the human microbiome in part determines the nutrition we obtain from the foods we eat.

Microbiomes are present throughout the food system, and touch on all aspects of sustainability. As such, designing sustainable food systems for the future must involve consideration of the microbial element.


Glossary

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The cheapest nutritionally adequate diet contains both plant- and animal-sourced foods

A recent paper published in Nature Food asked what foods would be in the cheapest diet that satisfies nutritional requirements. Combining the prices and food composition data for common food items in the US, the authors determined the cheapest way to feed one person a nutritionally adequate daily diet.

The cost of the diet was calculated as US$1.98 per day (NZ$3.02). It consisted of 15 foods, all of which could be found in the average US home kitchen. The top five contributors were milk, legumes, rice, potatoes and corn tortillas.

The authors also analysed what level of price increase to animal-sourced foods was necessary before the cheapest diet became entirely plant-based. Between 200-1,150% increases in the cost of animal-sourced foods was required, and the plant only diet would cost US$3.61 per day (NZ$5.51). The plant only diet overlapped with the original diet for many foods, but also included soy beverages, green peas and peanut butter.

The authors highlighted that the bioavailability of consumed nutrients was not considered in this study. Inclusion of bioavailability would likely increase the cost of both diets but would have a greater impact on the plant-based diet, due to the lower bioavailability of many nutrients in plant foods. The daily diets proposed by the authors are not recommended diets – a limit of 15 different foods is not feasible – but the work does show that animal-sourced foods can be a cost-effective way to get adequate nutrition.

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Australia’s changing landscape of protein production

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A study by the Australian Farm Institute tells us that despite the trend towards alternative proteins, large opportunities exist for animal proteins in the future.

The Australian population is growing, forecast to be nearly 29 million by 2030. This will inevitably result in an increased demand for protein. While alternative protein substitution has increased and will continue to do so in the next 10 years, this will not diminish the demand on animal agriculture. Rising demand for protein driven by that population growth will outweigh any additional market share that alternative proteins may gain. However, the current production systems have finite resources. Therefore, both animal and plant production will need to become more efficient and productive if Australia wants to avoid relying solely on food imports to sustain their future population

It is worth noting that the current global food system is plant-based and animal-optimised. Approximately 85% of all biomass leaving the world’s farms is plantsourced. For any sustainable food system to nourish the global population, both animal and plantsourced foods will continue to be required. Animal-sourced foods are particularly important to meet global requirements for micro-nutrients such as iron, zinc and vitamin B12. In fact, scenario testing of possible global food systems with the DELTA model repeatedly demonstrates that animal-sourced food production will not only continue to be needed to provide adequate nutrition to a global population, but that production will also need to be sustainably increased.

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Glossary

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‘Meat is part of a sustainable world’: Professor Louise Fresco

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Professor Louise Fresco (President of the Executive Board, Wageningen University & Research) argues that taking meat out of the food system is not the solution.

The future of the world will be characterized by eating less meat as we shift towards flexitarian and reductionist diets. However, meat should remain as part of a sustainable food system. Fresco highlights the valid point that grazing animals utilize land that cannot be used for anything else, converting inedible plants into valuable food. Nutrient-rich meat also becomes increasingly important, particularly with the aging population.

This is consistent with results from testing food production scenarios with and without meat for their ability to provide adequate nutrition for the global population, using the DELTA model. Key micro-nutrient requirements such as iron, zinc and vitamin B12 cannot adequately be sourced for the global population without the inclusion of animal-derived foods in the food supply system. In other words, animal-derived foods are necessary to nourish the global population. Meat, as well as dairy, should continue to be a part of our diets. However, effort must be made to ensure it is produced in the most sustainable way. This increases the pressure for research to reduce on-farm emissions, reduce water usage and improve water quality, and increase productivity from animal agriculture.

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Eat less red meat, scientists said. Now some believe that was bad advice

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An international collaboration of researchers concluded that the advice to eat less red meat is not backed by good scientific evidence.

If there are health benefits from eating less beef and pork, they are small, and not sufficient to tell individuals to change their meat-eating habits. Links are mostly in studies that observe groups of people, and even then, are only detectable in the largest groups.

This raises questions about the longstanding dietary guidelines urging people to eat less red meat. There have been concerns for years that red meat causes heart disease, cancer and other illnesses. However, if this is not backed by good scientific evidence it should not influence dietary guidelines. Red meat plays a key role in the contribution to multiple micro-nutrient requirements such as iron, zinc and vitamin B12. Research from the Global Burden of Disease study found that 11 million deaths and 255 million disability-adjusted life years were attributable to dietary risk factors, however the key risk factors were under-consumption of whole grains and fruits, and meat was found to have very little impact. It may be that high consumption of red meat is not inherently unhealthy, but rather a lack of choice and/or poor choice means a high level of red meat in the diet results in lower consumption of other healthy foods in the diet. In other words, is not red meat itself causing disease, but the lack of other foods as part of a balanced diet.

Therefore, it may not be in individual’s best interests to decrease red meat consumption, instead we should focus on consuming a balanced diet of healthy foods and sufficient nutrients.

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Animal-source foods for human and planetary health

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The Global Alliance for Improved Nutrition (GAIN) has published their position on the role of animal-sourced foods (ASF) in sustainably improving nutrition globally.

GAIN illustrates the importance of ASF in a nutritious diet. This is particularly important in reducing risk of undernutrition among vulnerable groups, especially children. It highlights the superior nature of ASF in terms of nutrient content and bioavailability, as well as the important contribution animal agriculture makes on livelihoods and ecosystems globally. The paper does acknowledge the environmental impact of animal sourced foods and the need for the livestock industry to do better.

It is possible for individuals on a vegan or vegetarian diet, if they have the resources and means, to meet their nutrition requirements through a combination of plant-based foods and relatively expensive supplements. However, this is not affordable and accessible for everyone. The GAIN paper highlights that people in low and middle income countries tend to especially be low in iron, vitamin A, zinc, calcium, and high-quality protein. Most low-income consumers in these nations would benefit from sustainably increasing consumption of animal-sourced foods to provide the nutrients needed for better health and development.

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Glossary

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The future food system must provide adequate nutrition to sustainably feed the global population


The philosophy of the Sustainable Nutrition Initiative (SNI) is to help create a better understanding of the food system and identify opportunities for improvement in order to sustainably feed the global population with the nutrients required. SNI has developed a modelling approach to test various scenarios for a globally sustainable future food system; The DELTA Model. This model is unique because it explores the ability of different food production scenarios to provide the bioavailable nutrients needed to adequately feed the global population. It does not try to provide the answer to the perfect sustainable diet for individuals. Rather, it aims to generate informed discussion about possible scenarios for future food production systems. This is critical, as a thinking failure today will lead to a system failure tomorrow. 

The fundamental principle of the DELTA Model is that for the global food system to be considered sustainable, it must deliver sufficient bioavailable nutrients to meet the nutritional needs of the global population. Having established the scenarios that can deliver this nutrition, it is essential to examine the associated environmental and socioeconomic consequences. Under such scenarios if the consequences are not acceptable, then a particular scenario is invalid and/or the performance of the environmental or socioeconomic outcomes need to be the focus for improvement.  However, a food system that optimises environmental and socioeconomic outcomes but fails to deliver the nutrition required is not sustainable. In this sense nutrition should come first in assessing future food production scenarios.

For the global food system to be considered sustainable it must deliver sufficient nutrients to meet the needs of the global population. 

According to FAO, a sustainable food system is defined 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. This means that:

  • It is profitable throughout (economic sustainability)
  • It has broad-based benefits for society (social sustainability)
  • It has positive or neutral impact on the natural environment (environmental sustainability)”

The beginning of the above definition is that food security and nutrition is met for all. This means that the food system must produce sufficient nutrients to meet global requirements. While it is essential to examine environmental and socioeconomic consequences, individuals should not be forced to starve or have nutrient deficiencies in efforts to protect the environment. There is no point in ensuring nutrition for future generations if the current generation cannot be sufficiently nourished. This is the basis for the initial phases of building the DELTA model. The Model starts with assessing nutritional needs and the ability of various food production systems to deliver to that nutritional need. 

Nutrition refers to supplying sufficient calories, macro-nutrients, micro-nutrients and trace elements

Individuals must consume sufficient calories and macro-nutrients – fat, carbohydrates and protein – to keep healthy. Protein consumed by the body supplies the  indispensable (essential) amino acids, which are the 9 amino acids that cannot be synthesised by the human body. These amino acids are required to manufacture proteins needed for bodily functions, such as building muscle, transporting nutrients and fighting infection. Essential amino acid deficiencies can result in a range of health issues including decreased immunity, digestive problems, lower mental alertness or slowed growth in children. Therefore, it is important to consider bioavailable essential amino acid supply and not simply protein when assessing a global sustainable diet. 

Equally as important to address are micro-nutrients and trace elements; the vitamins and minerals that are vital for human function. These are all too often overlooked to focus on energy, carbohydrates, protein and fat (the macro-nutrients). Micro-nutrient deficiencies, known as ‘hidden hunger’, are common contributors to poor growth, intellectual impairments, perinatal complications and increased risk of morbidity and mortality. Long term consequences occur not only at the individual level but have detrimental impacts on national economic development and human capital. A sustainable diet must deliver sufficient micro-nutrients to meet global requirements.

Many other models and recommendations of a sustainable diet compare nutrient composition against a generic adult recommended daily intake (RDI). However, this is inaccurate because RDIs vary depending on age, gender and a multitude of other factors. For example, according to New Zealand guidelines, females aged 19-50 require 18mg of iron per day due to loss through menstruation, while their male counterparts require only 8mg. Pregnant women require even more, with an RDI of 27mg/day. Since the DELTA Model takes a global view of the world feeding the world, the daily requirement per person per day is a weighted average based on the expected age and gender range of the population. It does not inappropriately apply the adult RDI for all individuals of the population.

Nutrient bioavailability must be considered

It is not enough to compare nutrient composition directly against requirements, the comparison must also take the bioavailability of individual nutrients in foods into account. Bioavailability refers to the proportion of a consumed nutrient that is absorbed into the bloodstream and used for normal body functions. Not all nutrients can be used to the same extent, depending on various internal and external factors. For example, haem iron, found only in meat, is more readily absorbed by the body compared to non-haem iron often found in plant foods. Haem iron also helps with the uptake of non-haem iron. According to Scientific American, only 1.4% of the iron in spinach can be taken into the body, while 20% of iron from red meat can be absorbed. On a composition basis, spinach has a higher iron content than beef; with 2.7mg/100g vs 1.9mg/100g. However once bioavailability is accounted for, to get the same amount of iron as in 100g of beef, 1.04kg of spinach needs to be consumed.

In addition, protein quality is not equal in different foods. Foods differ in their indispensable amino acid composition, and the bioavailability of these amino acids is affected by a range of food factors. Hence, it is not as simple as multiplying protein content by a single bioavailability factor. Digestible Indispensable Amino Acid Score (DIAAS) is a method to measure protein quality. It measures the true ileal digestibility of individual indispensable amino acids. A score of 1 or greater is considered a complete source of protein, while a score of less than 1 indicates the food is limiting in one or more indispensable amino acid. Using DIAAS, the score for wheat is 0.45, for oats 0.67, for peas 0.65, for soy protein isolate 0.84 and for cow’s milk 1.16. It is therefore vital to take protein quality into account, rather than simply comparing protein composition.

Other models and recommendations of a sustainable diet make the over-simplification that all foods are equal in bioavailability. The DELTA Model is an improvement against such models, because it adjusts for bioavailability when comparing nutrient supply against requirements.

The food system must be built from nutrient rich and bioavailable foods

In order to produce sufficient food to meet global requirements within global resource constraints, it is important to start with foods rich in bioavailable nutrients. Foods that deliver high bioavailable quantities of any nutrient in short supply, as part of an overall nutrient-rich profile are essential to ensure food systems will provide adequate nutrition for the global population. For most food production system scenarios that can be tested with the DELTA Model, it is often not the macro-nutrients that limit the provision of adequate nutrition.  Rather, it is the micro-nutrients and trace elements.  The limitations are most common where the greatest variance in bioavailability occurs. Foods rich in bioavailable nutrients are therefore required. For example, the richest and best-absorbed source of calcium is milk products, which is also rich in other nutrients such as high-quality protein and vitamins such as B12. On the other hand, the best sources of other nutrients, for example vitamin C are plants. This is why a balanced food system with nutrient-rich animal and plant foods is important.

Diets cannot work on a global scale if there are insufficient nutrient-rich foods. For example, suggested diets recomended by EAT-Lancet and Greenpeace suggest a reduction in animal products. While such reductions claim to be good for the planet, they do not necessarily guarantee global nourishment, particularly when it comes to micro-nutrients and trace elements like calcium, vitamin B12, zinc, iron and others. Nutritionist Zoe Harcombe found the EAT-Lancet diet is deficient in multiple nutrients, for example the diet provides only 55% of recommended calcium and 88% of the recommended iron. This is consistent with the DELTA Model, which also indicates it is not possible to meet global nutrient requirements with only plant-based sources of nutrition without supplementation and fortification, which may not be a practical or affordable solution on a global scale.

This does not mean the answer to the global food system is an abundance of animal foods. The current food system is plant dominant; in fact 85% of all biomass that leaves the world’s farms is plant-based. The key is that a food system must be optimised with nutrient-rich foods to ensure global nutrient requirements are met. In other words, the food system is, and should be, plant-based and animal optimised.

The options available to feed the world are not the same as options available to feed individuals, particularly those that can afford to, have a lot more choice in their foods and diets. This includes the consumption of fortified plant-based foods and supplements to meet their nutrient requirements. What might work for one individual does not necessarily work on a global level. The SNI has developed the DELTA Model to generate informed discussion about the possibilities of how the world can feed the world, not to dictate an individual’s diet. And for the world to feed the world, nutrient-rich foods are required.

Once we have established how the world can be nourished, other aspects of the food system must be considered

Once possible scenarios of how the world can be nourished are established, practicality of the food system and improvements required to deliver optimal outcomes must be considered. A solution that can nourish the average global citizen may not necessarily be a viable solution. Wider socioeconomic and environmental factors must be evaluated, such as land and its use, greenhouse gas emissions, water availability and quality, social and economic viability, and so forth. Under such scenarios if consequences are not acceptable, then a particular scenario is invalid and/or the performance of the environmental or socioeconomic outcomes need to be the focus for improvement. However, the DELTA Model puts nutrition first when assessing sustainable food production systems. Any food production systems that cannot adequately contribute to nourishing the world will likely be a sub-optimal use of the world’s scarce and valuable resources.


Glossary

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