Vitamin D and iodine
Non-essential amino acids include: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. These have not been included in the DELTA Model® as the internal processes the nutrients are involved in are challenging to account for accurately, and these nutrients can also be synthesised from essential amino acids. Essential acids isoleucine and valine are also not present in the DELTA Model® currently as they are rarely the limiting amino acid in the human diet. Inclusion of these nutrients in the model is being considered for future versions.
The DELTA Model® provides scenarios that indicate directional movement to determine any adverse outcomes in food supply and nutrient availability from various scenarios. This is not to say that the outcomes of such a scenario (e.g. no meat) will most certainly result in the simulated nutrient deficiencies, rather it alludes to likely outcomes of changes in production. Changes in future food production will be broad and nuanced, and it is imperative to ensure the direction that such changes shift global nutrient availability is adequate to feed our growing population.
A healthy human intestinal microbiome provides numerous services, such as supporting absorption of nutrients and acting as a protection against infection. An unhealthy microbiome can be linked to poor health. Research insight has suggested that although a correlative relationship has been found between microbiomes and disease, the underlying processes that would determine a causal relationship are uncertain. As such, the role of the intestinal microbiome in nutrition is beyond the scope of the DELTA Model®.
Global averaging of nutrient availability
DELTA assumes an equal distribution of food globally and produces an average nutrient availability for the global population. This does not capture the realistic distribution of food that is inequitable across the world. This is because the DELTA Model® considers nutrient adequacy at a global scale and provides insight on various food system scenarios and the capability to produce nutrition for all. Both the individual and the global perspectives, and thus both modelling approaches, are necessary when considering the aptitude of the food system. DELTA does include historic information of on the distribution of nutrients at a country level, which provides come insight into the range of availability. However, there are too many variables to project this variation onto future scenarios, and insufficient data to look at the variation in intake or availability within countries.
Demand versus requirement
DELTA considers only nutrient requirements. Nutrient demand, where the specific nutrients and amounts are determined by consumers, is quite different and is not captured by DELTA Model®.
The current version of the model contains good data for protein and amino acid bioavailability. For iron and zinc, the availability of data for individual food items is not as great, therefore bioavailability is captured by changing nutrient requirement values. Due to insufficient bioavailability data for all other nutrients, no consideration of bioavailability is made for these.
Nutrient absorption is dependent on the meals and food combinations people make in their diet. Individual diets are beyond scope of DELTA, and thus meal effects are not captured.
The strength of the model’s nutrient requirement estimates are dependent on the EFSA data source. For some nutrients, limited data is available on human requirements, whereas for others there is sufficient data for all age and gender groups to set upper and lower bounds on intake, as well as target intakes.
The FAO data that informs the model has limitations. Some countries are missing data, and the quality of data reported varies between countries. Moreover, inhome waste estimates are at a regional and food group level. Unfortunately, this data is the best currently available and is sufficient for directional conclusions on future changes to the food system.
Currently, food items are grouped into 15 food groups for ease of use by a broad audience. This means that any increase in the total production of a food group causes a proportional increase in the production of each food item within it, following the distribution in the baseline data set. This increase is carried through all model calculations: waste, other uses, and the available nutrients. Future versions of the model may allow for user input at a higher resolution.