FAO’s estimates of the prevalence of undernourishment are essentially a measure of food deprivation based on the calculation of three key parameters for each country: the average amount of food available for human consumption per person, the level of inequality in access to that food and the minimum number of calories required for an average person.
Average food available for human consumption comes from national “food balance sheets” compiled by FAO every year which estimate how much of each food commodity a country produces, imports and withdraws from stocks for other non-food purposes. FAO then divides the energy equivalent of all the food available for human consumption by the total population to come up with average daily energy consumption.
Data from household surveys are used to derive a coefficient of variation to account for the degree of inequality in access to food. Similarly, since a large adult needs almost twice as much dietary energy as a three-year-old child, the minimum energy requirement per person for each country takes into account its mix of age, gender and body sizes.
The minimum level of dietary energy requirement is derived from the FAO/WHO/UNU Expert Consultation in 2001, which established energy standards, published in 2004, for different sex and age groups performing sedentary physical activity and with a minimum acceptable body-weight for attained heights.
The average energy requirement is the amount of food energy needed to balance energy expenditure in order to maintain body-weight, body composition and a level of necessary and desirable physical activity consistent with long-term good health. This includes the energy needed for the optimal growth and development of children, for the deposition of tissues during pregnancy, and for the secretion of milk during lactation consistent with the good health of mother and child. The recommended level of dietary energy intake for a population group is the mean energy requirement of the healthy, well-nourished individuals who constitute that group.
FAO reports the proportion of the population whose daily food intake falls below that minimum energy requirement as undernourished. Trends in undernourishment are mainly driven by:
- Changes in food consumption as measured by country Food Balance Sheets;
- Changes in the variance of the distribution of dietary energy consumption in the population, induced by changes in both the distribution of dietary energy consumption due to income levels, and the distribution of dietary energy requirements based on weight for attained heights by sex and age; and
- Changes in the minimum level of dietary energy consumption, induced by changes attained heights and the sex-age population structure.
This indicator has been defined within a probability distribution framework as follows:
- P(U) is the proportion of undernourished in total population;
- (x) refers to the dietary energy consumption or intake;
- rL is a cut-off point reflecting the minimum acceptable dietary energy consumption;
- f(x) is the density function of dietary energy intake; and,
- Fx is the cumulative distribution function.
In developing the methodology for estimating the prevalence of undernourishment, a basic problem concerns the use of energy requirement norms and energy consumption for individuals. Even after taking into account the most influential factors such as age, sex, body weight and activity, differences exist in the energy requirement of individuals. As it is not feasible to determine energy consumption of individuals, the estimate of the proportion of individuals with insufficient energy consumption is defined within a probability distribution framework.
The graph below illustrates the methodological framework for the estimation procedures of the proportion of population who are undernourished.
In the graph above, the curve f(x) depicts the proportion of the population corresponding to different per person dietary energy consumption levels (x) represented by the horizontal line. The area under the curve up to the minimum acceptable dietary energy consumption, rL, represents the proportion of the population below minimum level of dietary energy consumption or the proportion of the population undernourished, i.e. prevalence of undernourishment, pU.