Calculation of footprint for food and drink

Calculate a person’s food and beverage consumption and resulting household waste from dietary habits. The output is expressed in weight, footprint and cost, and can be used to efficiently nudge users towards more sustainable consumption.

All inputs, outputs and defaults can be seen in the Calculate food and drink technical API docs.

Inputs

This endpoint receives:

• a data source to base calculations on
• a list of dietary habits
  • How much do you eat? 
  • How much dairy is in your diet?
  • How much food do you throw away?
  • How often do you eat meat?
  • How often do you eat seafood?
  • What is your meat preference?
  • What is your seafood preference?
• age
• the date for which the footprint should be computed

The more input is given the better we understand the user’s behaviour, giving a more accurate footprint estimation. All inputs are optional and missing values are defaulted. If no input date is given, the current date is used as default. If no habits are provided the calculation will assume default answers, i.e. that your diet is similar to an average person from the data source you have specified. This can be used to compare a person's food and drink footprint to the average person in a country.

Outputs

This endpoint returns both total amount and amount per subcategory for each variable:

If you have not submitted optional information, the weight, footprint and cost of an average person’s diet for the chosen data source will be returned.

Calculation

Diet composition

The composition of different diets is based on the work of Stamm et al. In principle, we construct the diet of an average individual based on the amount consumed of different food categories. 

Food and drink multipliers

The detailed food categories used in the calculation are aggregated up to higher level categories as detailed in the Conversion of food and drink endpoint, which are returned in the output of this endpoint. Each food category is associated with a CO2e multiplier. The multipliers are calculated based on food consumption habits from the NORKOST food consumption survey, which gives insights into the different types of food consumed by the average Norwegian. On top of this, we also take into account the environmental impact of transporting the foods from the site of production to the site of consumption. Studies have shown that transportation is responsible for 6% of the total emissions across the food supply chain. We use this information to calculate the emissions arising from the transportation of food products.

The input date also affects the calculations. We take into account the technological changes over time (sustainable farming methods, fossil-free fertiliser production) and their impact on your footprint.

Diet adjustments

We ask the users a set of questions which help us analyse their diet better. Based on the user's inputs, the diet is adjusted. For the input on diet amount, the overall amount of calories eaten is scaled by a factor, assuming that the increase in calories eaten is equal for all categories. 

Diet adjustments for meat and shellfish

For the input on meat and seafood-eating habits, calories previously allocated to meat and seafood categories are reallocated to plant-based food categories. The calculation assumes that the overall number of calories consumed are the same for different diets. As you might already know, meat consumption has the highest impact per calorie of all the food groups. On average, meat production emits three times as much CO2 emissions per calorie than the production of the average vegetable , so a reduction in consumption of the former will reduce the footprint. 

Additionally, ruminant animals like cows and sheep have digestive systems that work very hard to break down grass, and produce a lot of methane gas that they emit via burps. Methane is a powerful greenhouse gas, although it disappears more quickly from the atmosphere than CO2. It is counted in the overall footprint in CO2 equivalents, where it’s given a factor reflecting both its greenhouse effect and lifetime. Note that the environmental impact will vary based on what kind of meat you consume. For example, the environmental impacts of white meat like chicken are much lower than that of red meat like beef. The habit question regarding preference of meat takes this into account. If a person prefers white meat over red meat, some calories of red meat are reallocated to white meat. As the environmental impact of white meats is lower compared to red meats, this would result in a reduced footprint.

Diet adjustments for dairy products

Since dairy products are associated with animal husbandry, they are also associated with high environmental impacts for the reasons described above. Specifically, milk, yoghurt and cheese have high emissions per calorie content, comparable to the average emissions of plant-based products. If you’re a vegan (or lactose intolerant), you can also input this, and the calculator will attribute those calories to other categories.

Food waste

Food waste represents an efficiency loss, and thus is associated with an environmental impact. If we lower food waste at the household level, this food will not have to be produced, and will result in an emission reduction. The food waste can be divided into supply chain waste (in the food industry, at the distributors, and in grocery stores) and household waste. The data for value chain and household food waste for different types of foods is obtained from the NORSUS report “Matsvinn i Norge” (Norwegian only).  The food waste at household level is affected by a person’s age and this is replicated in our calculations. The correlation between age and household food waste is explored in the NORSUS report “Kartleggingsrapport for matbransjen og forbrukerleddet“ (Norwegian only). Both reports are made for the industry association Matvett. For countries other than Norway, a single food waste factor is applied to all food categories and this factor is influenced by only the user’s food habits.

Converting between weight, calories and cost

The weight consumed of each food type is calculated by combining the  calorific densities (kcal/g) of the respective food types, obtained from Matvaretabellen, with the calories consumed. To estimate the amount of money spent on different food categories, we combine the monetary factor (Currency/kg) of a food category with its consumed weight (in kg). The monetary factors are obtained by combining SSB data on food and beverage consumption with spending amounts from the Consumer Expenditure Survey.