The Optimeal® tool for healthy, sustainable food products and diets

Both individual consumers and the food industry are increasingly considering the dual impact of their food on health and the environment. Quantifying how sustainable certain foods are is challenging, but the Optimeal® tool allows you to look at this question in detail.

Optimeal was developed in the Netherlands and has contributed to several scientific publications around the sustainability of diets. You can enter a daily diet into Optimeal, and ask it to optimise the diet for nutrition, or to minimise the environmental impact of the diet, or even to replace a certain food item with nutritionally equivalent foods. Optimeal then returns an altered diet that answers the question posed with the minimum degree of change to the original diet. This helps to ensure that the new diet would still be acceptable, due to its similarity to the original diet. 

Optimeal can also be used in food product development. For example, a food developer may wish to reduce the environmental impact of a new ready-meal, while ensuring that it meets some constraints around nutrition. Optimeal would optimise the increases and decreases needed to the ingredients in the meal that satisfy the developer’s requirements. 

Optimeal differs from the Sustainable Nutrition Initiative’s DELTA Model in the scale of sustainability it considers. Optimeal is excellent for analysing food and diets from an individual up to a national level, whereas the DELTA Model considers the sustainability of the global food system. Considering sustainability from the individual and the global perspective are both important in designing future food systems.


Photo by Caroline Attwood on Unsplash

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

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.


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

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

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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Build a food system from nutrient rich foods first

The philosophy of the Sustainable Nutrition Initiative (SNI) is to help create a better understanding of our food systems and identify opportunities for improvement. This is to ensure that in the future we can sustainably feed the global population. SNI has developed a modelling approach to test any range of possible scenarios that could contribute to globally sustainable food systems; 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. The Model does not try to identify or prescribe options for diets for individuals, as there are many ways individuals, particularly those with money and access to different food types, can meet their nutrient requirements. Rather, it enables the creation of scenarios to inform discussions about possible future food production systems that meet the nutrient requirements of the entire population.

A critical feature of a sustainable food system is that the food produced is sufficient to provide the bioavailable nutrients required by the global population. However, there are imbalances in the production and consumption of these nutrients, causing a range of health issues. There is also sub-optimal use of resources, including environmental resources, to produce and distribute food. Globally, the current food system provides sufficient energy and macro-nutrients, but not sufficient micro-nutrients and trace elements, to meet global requirements. Therefore, production and consumption of nutrient-rich foods, particularly those that address micro-nutrient and trace element deficiencies, should be a priority.

There is an increasing challenge to feed the world within global resource constraints

The target of the global food system is to meet nutrient requirements of the global population. This includes all nutrients that humans must obtain from their diet to survive and thrive; energy, macro-nutrients – including essential amino acids as part of overall protein, micro-nutrients and trace elements. However, the earth has limited resources. There is a limit to the amount of food that can be produced before we run out of land, water and other resources. Not all food production scenarios are practical within these constraints. It is therefore a challenge to use resources optimally to ensure all nutrient requirements are met.

The global food production system produces enough energy to feed the world, but problems arise from lack of choice or poor choice

The current food system already has sufficient, even an abundance of energy and macro-nutrients to feed the global population. According to FAO, the world produces around 2,900 calories, 83 grams of protein, and 84 grams of fat per person, per day. This is more than enough to meet the average human requirements. There are however imbalances in the production and consumption of such nutrients. The reason that 11% of the world is undernourished is because of the inequality in access to food (distribution and affordability), rather than production scarcity. Other health issues caused by an under or over consumption of energy arise from a lack of choice or poor choice.

There is not enough production of some micro-nutrients to feed the world

While there is evidence that global food production can feed the world on a calorific basis, the micro-nutrient and trace element requirements of the global population may not be able to be met, even with perfect distribution and zero waste.

According to WHO, an estimated 2 billion people have a micro-nutrient or trace element deficiency (including clinical and sub-clinical deficiencies). Micro-nutrient and trace element deficiencies are common contributors to poor growth, intellectual impairments, and increased risk of morbidity and mortality. This is often referred to as ‘hidden hunger’; it doesn’t always cause death in the way protein-calorie hunger does. Instead it often results in individuals ‘surviving but not thriving’. Long-term consequences occur not only at the individual level but have detrimental impacts on national economic development and human capital. The most common deficiency is iron which affects a quarter of the global population. In some cases, these deficiencies are due to poor dietary choice, but others are due to a lack of choice resulting from limited access.

The DELTA Model shows that if all food that is currently produced was distributed evenly globally, there would still be shortages against requirements for some micro-nutrients and trace elements such as calcium, iron and zinc. In other words, the global food production system currently cannot provide sufficient micro-nutrients and trace elements to feed the world. This indicates resources are not being used to produce food that is optimal for meeting human requirements.

The food system should prioritise nutrient-rich foods

To ensure that the food we produce has sufficient nutrition to feed the global population, while still staying within the constraints of planet earth, nutrient-rich foods should be prioritised. The food system should be built from foods that deliver highly bioavailable quantities of micro-nutrients. This is particularly important for the nutrients in short supply (like calcium, iron and zinc), but as part of an overall nutrient-rich profile.

For example, the richest and best-absorbed source of calcium is cow’s milk and its derivatives. Other foods show high concentrations of calcium; however, bioavailability is variable. Milk is an efficient source of calcium in the food system. But the real benefit lies in dairy being a balanced source, rich in multiple nutrients other than calcium, including high-quality protein, zinc, vitamin B12 and riboflavin.  

For iron, the best sources come from animal-sourced foods, including red meat. This is because the bioavailability of haem iron from animals is much greater than non-haem iron from plant sources. Haem iron also helps the absorption of non-haem iron. Therefore, it is important to have sufficient red meat, alongside plant-sourced foods in the system to meet global iron requirements.

Of course, animal-sourced foods are not the richest source of every micro-nutrient and trace element. For example, vitamin C is best sourced from plants. The key is that starting with foods rich in bioavailable nutrients helps to ensure the global nutrient requirements are met, while using the limited production resources in the most efficient way.

If the food system is built up from the most nutrient rich foods first, energy as well as other macro-nutrients will naturally be met, as these are inherent in food groups. For example, milk also contains fat and protein, as well as the micro-nutrients and trace elements as explained above. Therefore, improvement and optimisation of food systems should place priority on nutrient rich foods.


Photo by Louis Hansel @shotsoflouis on Unsplash

Food choice varies by individual context

The philosophy of the Sustainable Nutrition Initiative (SNI) is to help create a better understanding of our food systems and identify opportunities for optimisation and improvement. This is to ensure that in the future we can sustainably feed the global population. SNI has developed a modelling approach to test any range of possible scenarios that could contribute to globally sustainable future food systems; 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 uses scenario testing to generate informed discussion about possible future food production systems.

The options available to feed the world are not the same as the options available to feed individuals. Individuals, particularly those that can afford to, have a lot more choice in their foods and diets, including fortified foods and supplements to ensure their nutrient requirements are met. However, the world’s poorest already spend a large percentage of their income on food and have limited ability to spend more on food. This problem intensifies if food becomes more expensive as a result of changes in global production. Therefore, any recommended changes to food production systems need to ensure that the food they produce is affordable on a global basis. Furthermore, certain diets are not practical at a global level as they would require significant and costly changes to food production and distribution systems. The focus of improving and optimising food systems should be on how the world’s total food production can feed the world’s total population, not dictating an individual diet.

Some individuals have flexibility in their choice of diet

The primary focus of any sustainable food system is to meet nutrient requirements of the population. Looking on an individual scale, all nutrient requirements including macro-nutrients, essential amino acids, and micro-nutrients and trace elements must be satisfied to ensure health and wellbeing. An individual with the wealth and means is likely to be able to meet such requirements on any given diet. Those that can afford it can select a range of nutritious foods and take supplementation and fortified foods where required.

One example is a vegan diet. By omitting meat and dairy, it can be harder to reach the required intake of bioavailable essential amino acids and micro-nutrients, such as such as calcium, iron, zinc and vitamin B12. This is because such nutrients are best sourced from animal-based food groups. However, it is possible to meet nutrition requirements through plant-based foods only with the addition of processed fortified foods and/or supplements to provide the essential micro-nutrients that plant-based foods are often poor sources of. An individual with the wealth and means can consume a variety of nutrient-rich plant-based foods to meet the majority of their nutritional requirements. For example, nuts are high in protein, and pulses contain vitamins and minerals such as folate, iron and zinc. Individuals must also ensure they are consuming a variety of protein sources to ensure they meet their requirements for all essential amino acids, particularly lysine which is often the most limiting amino acid. Most plant-based foods are not complete sources of all essential amino acids. However, if a variety of sources are consumed as part of a meal, requirements can be satisfied.

Not all diets are affordable by everyone

However, some of these choices are only affordable and accessible to wealthier individuals in some parts of the world. The world’s poor spend a much higher proportion of their income on food. The lowest expenditure quintile of the population in Ghana for example, spend over 70% of their household budget on food. Within the US, the lowest income quintile spends approximately 35% of their income on food, while the highest quintile spends only 8% (figure 1). Those that are wealthy have greater flexibility to change their expenditure on food and supplementation as required to fit their chosen diet and lifestyle. Unfortunately, not everyone has this opportunity.

Food spending as a share of income declines as income rises
Figure 1: Food spending and share of disposable income spent on food across US households, 2018

Changes in global food production can make food even more expensive. For example, a significant increase in production of pulses and nuts to meet a global vegan diet would require increases in prices to incentivise suppliers to move away from production of other profitable crops or livestock. Supply of some products may not be able to react quick enough to meet demand, for example tree nuts can take 3 to 10 years before the trees start producing nuts. This will further drive up prices.

However, as prices increase, food unaffordability on a global scale will increase. Research that reviewed 1600 US-based studies on food price elasticity found the value of mean price elasticity to be about -0.60 for cereals and vegetables. This means if the price of cereals and vegetables were to increase by 25%, demand would decrease by approximately 15% globally. These drops in demand would be greater for lower-income households compared to higher-income households, as food is more likely to become unaffordable as prices increase. As a result, the poor, who already struggle to consume adequate nutrients, will be able to afford even less. Even more modest increases in price will render many households unable to afford the food they need.

Changes in diets on a global scale have impracticalities in terms of cost and time required to make the change

Making changes to diets on a global scale may require significant changes to the global food systems in terms of the size of the change and time required, and therefore may not be practical. For example, the world adopting a solely vegan diet as mentioned above, would require land and resources to be converted from livestock to crop production. Production of nutrient-rich plant-based foods such as nuts and legumes would need to be significantly increased. It is one thing to change attitudes, but physical changes to the food systems can be much more difficult. Physical resources would need to be re-allocated, bearing a large cost and requiring a significant amount of time. Cutting animal production would also affect the one billion people who rely on livestock for food and livelihoods.

The focus of improving and optimising the food system should be on the world feeding the world, not dictating an individual diet

Freedom of choice about food can work at an individual level where people have the wealth and means to select the food they want. However, there is no ‘one size fits all’ when it comes to what the world should eat. Diets will vary based on economic and social factors such as income, culture, religion, geographical location and so forth. Moving the entire world to a given diet can result in many being unable to afford nutrition, or costly and time-consuming changes to food systems. Instead, the focus of improving and optimising the food system should be on how the world can feed the world. The scenario-based approach that the DELTA Model allows users to analyse different possibilities of how the world’s total food production can feed the world’s total population. It does not dictate an individual diet, rather it focuses on improvement and optimisation of future food systems. 


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Study shows the EAT-Lancet diet is unaffordable for at least 1.6 billion people

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A study has found the EAT-Lancet diet is unaffordable to 1.6 billion people, mostly in sub-Saharan Africa and South Asia.

The ‘planetary health diet’ costs a median of USD $2.84 per day, which is about 60% more expensive than a diet that meets our minimum nutritional requirements. The study found that the diet costs between 3% to 73% of national average incomes. Fruit and vegetables and animal-sourced foods are the most expensive components of the EAT-Lancet reference diet.

The EAT-Lancet diet has many flaws, it is not the perfect diet. But it generates good discussion about what needs to be done to make a healthy and sustainable diet affordable for the global population. A cost-effective diet must be optimised on cost per nutrient or bundle of nutrients. The issue with the EAT-Lancet reference diet is that it involves switching from low cost sources of nutrition to more expensive sources to deliver the nutrients we need. Even then, the EAT-Lancet diet falls short on supplying nutrients such as iron and calcium in adequate amounts, and the protein quality of the diet is lower.

Furthermore, switching to more expensive sources of nutrition means supply and demand can get out of balance due to demand increasing from those who can afford those foods. Supply may not be able to react quick enough, for example, tree nuts take 3 to 10 years before the trees start producing nuts. As a result, prices will increase, and food will become even less affordable to some of the population.

To make a sustainable diet affordable by the global population, the cheapest source of quality, bioavailable nutrients should be prioritised. For example, in the US, dairy is the lowest cost source of dietary calcium, riboflavin and vitamin B12, and should therefore be prioritised.

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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.


Photo by Valeriy Evtushenko on Unsplash