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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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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An optimal food system is a practical one

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.

A possible food system is one which provides sufficient nutrition to nourish the global population. Once a possible food system is identified, the practicality of implementing this must be considered in terms of the level of change required, the feasibility of the changes, and more importantly, the time taken to implement the required changes. Once possibility and practicality are considered, the food system can be optimised based on other environmental and socioeconomic factors. There is not necessarily one correct answer for what the optimal food systems are. However, it is important to think about the food system in the right way. A thinking failure today will lead to a system failure in the future.

A sustainable food system must deliver the bioavailable nutrients required to nourish the global population.

A possible food production scenario is one which provides sufficient nutrition to feed the global population. Nutrition must come first in any discussion of a food system. Therefore, only food systems that can adequately nourish the world can be considered as sustainable. Not only must the food system have sufficient energy (calories) to feed the world, it also must deliver sufficient fat, protein and carbohydrates (the macro-nutrients), sufficient essential amino acids as part of overall protein, and the required micro-nutrients and trace elements. Further to this, it must account for nutrient bioavailability – the proportion of a consumed nutrients that are actually utilised by the human body.

Based on these criteria, there are likely to be limited choices in what can be considered as “sustainable food systems”. The DELTA model allows users to test diverse scenarios and identify those that could contribute to sustainable global nutrition. The model uses food production information to predict the nutrition available to the average global citizen and compares this against requirements. Where a certain scenario meets requirements, it can be considered as possible.

It is worth noting that individuals are not limited in their choice to the same extent as the world is. 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, what might work for one individual does not necessarily work on a global level.

Not all possible food production scenarios are practical

Once possible food systems are identified, the practicality of implementing the system must be considered. A practical food system is one which has the ability to change and accommodate consequences over a quick enough time period to create a sustainable food system needed by future populations.

Any modification of the food production system will require changes in resource allocation and utilisation, food prices, consumption habits etc. The food system is very complex with multiple inputs, outputs and feedback loops. Planet earth’s resources are limited and are presently allocated for the food that is currently produced and consumed. One billion people currently rely on livestock for their livelihoods. Therefore, any material changes to the types and quantities of food produced will bear significant costs. It is one thing to change global attitudes but making changes in physical resources can be much more difficult. Some scenarios may simply not be feasible due to limited resources such as land.

It is critical to consider the time required to implement such changes. The world is looking to deliver the Sustainable Development Goals by 2030. It is important to be well on the path towards creating a sustainable food system by then. More importantly, while making any changes to feed future generations, current generations must still have access to affordable nutrition. In other words, we cannot put the food system “on hold” while re-inventing it.  If a food system cannot be implemented and make all the necessary changes quickly enough to meet the needs of future generations, then it cannot be considered practical.

Practicality in terms of affordability must be considered

As part of changes required, affordability must be considered. Changes in a food production system can impact the affordability of food. For example, if a proposed food system is higher in more expensive sources of nutrition then it may not be affordable for all. The EAT-Lancet reference diet suggests a diet that is healthy for people and for the planet. However, a recent study found this diet is unaffordable for 1.6 billion people. Moving to more expensive diets may mean a food system is not practical as many cannot afford to get the nutrition they require.

Further to this, as production levels of food groups change, food can become more expensive. Producers require a substantial increase in price to incentivise them to increase production, particularly if this means moving away from production of other profitable products. Supply of some products may also not be able to react quick enough, for example tree nuts can take 3 to 10 years before the trees start producing nuts. This will further drive up prices.

However, if prices increase, demand will start to drop off. Food will become unaffordable to many, particularly those already struggling to buy adequate, high-quality nutrition. A study found the value of mean price elasticity globally to be -0.60 for cereals and -0.58 for vegetables. This means if the price of cereals and vegetables were to increase by 25%, demand would decrease by approximately 15% globally. Lower income countries will experience greater decreases in demand, as food is more likely to become unaffordable as prices increase. Therefore, these regions which already struggle with meeting their nutrition requirements will be able to afford even less. As a result, the global population would not be sufficiently nourished, and that food system could not be considered practical. Practical food systems must be affordable.

The optimal food system must therefore be a practical one

Once possible and practical food systems are identified, they should be optimised based on other environmental and socioeconomic factors, such as greenhouse gas emissions, water utilisation and quality, economic growth etc. A food system that is possible and practical may have unacceptable environmental or socioeconomic consequences. This food system therefore cannot be considered optimal, or these consequences must become a focus for improvement.

There are no clear solutions as to what the optimal food systems are. However, what is important is that optimal food systems must be practical in terms of the changes required to implement them. And to be practical, it must be possible to provide sufficient nutrients to meet global requirements. Any discussion of an optimal food system needs to be constrained by what is practical or it becomes a utopian dream. The right thinking is essential, as a thinking failure today will lead to a system failure in the future. The scenario-based approach that DELTA Model takes enables the informed discussion and planning that is needed to avoid future failure.


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