Our Actions are our Future: Grow, Nourish, Sustain. Together.
Today – Friday 16th October – is World Food Day, the 75th anniversary of the founding of the Food and Agriculture Organisation of the United Nations with its goal to achieve food security for all and make sure that people have regular access to enough high-quality food to lead active, healthy lives. We congratulate the FAO on reaching this anniversary and all the good work the organisation does.
At the same time, it is a day for all of us to reflect on the challenges facing the global food system. Despite advances in agricultural production methods and yields, we fail to produce and distribute sufficient food to nourish an increasing global population. Many production systems are damaging the natural resources on which they or other food production systems rely, and many food producers receive subsistence income from their products. The 2030 Sustainable Development Goal (SDG) of Zero Hunger looks as far away today as it did when the SDGs were first developed.
Over 2 billion people do not have regular access to safe, nutritious and sufficient food whilst the global population is still growing and expected to reach almost 10 billion by 2050.
Nearly 690 million people are hungry, up 10 million since 2019. The COVID-19 pandemic could add between 83-132 million people to this number.
The impact of malnutrition in all its forms – undernutrition, micronutrient deficiencies, as well as overweight and obesity – on the global economy is estimated at USD 3.5 trillion per year.
Today, only nine plant species account for 66% of total crop production, despite the fact that there are at least 30,000 edible plants. We need to grow a greater variety of foods to better nourish people and sustain the planet.
Approximately 14% of food produced for human consumption is lost each year between the “farm” and the wholesale market. Even more food is wasted at the retail food and consumer stages.
Our ability to effectively nourish an increasing global population is one of the key challenges facing the human race. The global food system is incredibly complex, the world’s largest economic sector, with multiple inputs and outputs. It is often politicised, is subject to various socio-cultural forces, and touches every human being on the planet. Charting a course for the food system of the future requires quality thinking and discussion built on strong evidence-based foundations.
The DELTA Model has been developed to help people explore different futures for the food system for themselves.
The goal remains to achieve food security for all and make sure that people have regular access to enough high-quality food to lead active, healthy lives. We can all help towards this through understanding the food system in all its complexity, strengths, and weaknesses, leading to better informed discussion on the future of food for all of us.
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.
Amino acid bioavailability (% of total consumption that is absorbed)
94 – 99
81 – 94
Cooked kidney beans
64 – 100
70 – 88
47 – 66
75 – 99
78 – 97
71 – 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.
Limiting amino acid(s)
Leucine and Valine
Pea protein concentrate
Methionine and Cysteine
Skim milk powder
Methionine and Cysteine
Soya protein isolate
Methionine 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.
Vegetables grown at higher carbon dioxide (CO2) concentrations may grow better but may not have the same nutritional benefits.
Increasing atmospheric CO2 concentrations have prompted research into the effect of this phenomenon on plant growth. In general, elevated CO2 is good for plant growth, increasing yield and environmental stress tolerance. However, a review of the research in this fieldhas found that elevated CO2 also reduces the magnesium, iron and zinc content of vegetables. This reduction was as much as 31% for iron in leafy greens.
In specific vegetables, the review found that sugar content of lettuce, tomatoes and potatoes increased at higher atmospheric CO2 concentrations, while protein content decreased. Other factors, such as antioxidant content, were strongly affected, but this effect was different between different vegetable cultivars.
Higher yields with lower protein content have also been found for staple crops and grains grown at elevated CO2 concentrations. These changes occurred alongside reduced iron and zinc content.
In a future with increased atmospheric CO2 concentrations, our crops and vegetables may grow larger and sweeter, but the amounts of other essential nutrients that we get from them may decrease. This could lead to higher caloric intakes required to obtain the same amount of nutrients from these foods. While the concentrations reviewed in this publication were high compared to those expected in the near future, we should be prepared for some degree of impact on our crops. Targeting crop varieties which make the best of the changing conditions is being explored.