Food balance sheets present a comprehensive picture of the pattern of a country's food supply during a specified reference period. The first attempts at preparing food balance sheets date back to World War I. Food balance sheets were the major source of data when, in 1936, at the request of the League of Nations Mixed Committee on the Problem of Nutrition and its Sub-Committee on Nutritional Statistics, a systematic international comparison of food consumption data was prepared.
During World War II, the interest in food balance sheets increased considerably. The Inter-Allied Committee on Post-war Requirements used them in 1942/43 in their studies of post-war requirements in European countries and an even more detailed technique was developed and employed by a joint committee of experts from Canada, the United States of America and the United Kingdom in the report "Food Consumption Levels in the United States, Canada and the United Kingdom". During these years, food balance sheets were also constructed in Germany for the country itself as well as for the occupied countries. In the work of the International Emergency Food Council, which dealt with problems of food allocation and distribution in the period of worldwide food shortages after the war, food balance sheets played an important role.
From the outset, the Food and Agriculture Organization of the United Nations (FAO) has given considerable importance to furthering the development of food balance sheets, reflecting their usefulness in analyzing the food situation at the level of individual countries. At its Fourth Session in Washington in 1948, the FAO Conference recommended that governments be encouraged to develop their own food balance sheets and that FAO assist those governments that find it difficult to do so. It was also proposed that in future food balance sheets be published regularly for as many countries as possible.
In 1949, the Handbook for the Preparation of Food Balance Sheets was printed. In the same year, food balance sheets were published for 41 countries covering the period 1934-38 and 1947/48, with a supplement in 1950 giving 1948/49 data for 36 countries. In 1955, food balance sheets giving 1950/51 and 1951/52 data were published for 33 countries, together with revised data for the 1934-38 period. Supplements were issued in 1956 giving 1952/53 data for 30 countries, and in l957 giving 1953/54 and 1954/55 data for 29 countries.
For methodological reasons, it was decided in 1957 to discontinue the publication of annual food balance sheets and to publish instead three-year average food balance sheets. The first set of which, for 30 countries, was issued in 1958, covering the period 1954-56; the second for 43 countries in 1963, covering the period 1957-59; the third for 63 countries in 1966, covering the period 1960-62 and the fourth in 1971 for 132 countries, covering the period 1964-66. In 1960, time series covering the periods 1935-39, 1948-50, 1951-53 and 1954-56 were published showing data for 32 countries on production, available supply, feed and manufacture, as well as per caput food supplies available for human consumption in quantity, caloric value and protein and fat content.
In 1977, it was possible to publish provisional 1972-74 average food balance sheets for 162 developed and developing countries. For the first time, tables were included showing for all countries, continents, economic classes and regions and the world, long-term series of per caput food supplies in terms of calories, protein and fat by major food groups for the average period 1961-63 and individual years 1964 to 1974. The following issue included 1975-77 average food balance sheets for 164 countries, together with long-term series of per caput food supplies and tables showing the conversion ratios applied and the various assumptions made in arriving at the published figures. For the first time in this series, the table of per caput food supplies also showed, in addition to calories, protein and fat, the supply by food groups of selected minerals (iron, calcium) and vitamins (retinol, thiamine, riboflavine, niacine, ascorbic acid).
Starting with the 1979-81 issue, three-year average food balance sheets were published in a standardized format; 146 countries were covered. The publication showing standardized food balance sheets for the average 1984-86 included, in addition to the food balance sheets for individual countries, tables showing long-term series of per caput supplies, by major food groups, in terms of product weight, calories, protein and fat. These tables were shown also for the world, developed and developing countries. The tables were based on information for more countries than those included in the publication, and covered almost 100 percent of the population in both developed and developing countries. The 1992-94 issue covered 175 countries and the 1994-96 issue about 180 countries.
Food balance sheets were the main source of data used in the assessment and appraisal of the world food situation which FAO made for the pre-war period in its First World Food Survey (1946), for the early post-war period in the Second World Food Survey (1952), for the late 1950s in its Third World Food Survey (1963), for the early 1970s in its Fourth World Food Survey (1977), for the 1970s and 1980s in the Fifth World Food Survey (1985) and, covering the two decades from 1969-71 to 1990-92, in the Sixth World Food Survey (1996) . Food balance sheets also provided a major source of information for establishing the statistical base of FAO's Indicative World Plan for Agricultural Development, for which purpose 1961-63 average food balance sheets were prepared for all the 64 developing countries included in the study.
In constructing the food balance sheets, both official and unofficial data available in the Statistics Division and other Units concerned in FAO have been used and missing data have been estimated on the basis of surveys and other information as well as technical expertise available in FAO. Comments on the previously published average food balance sheets and suggestions for their improvement received from countries have also been taken into account.
To restate, food balance sheets present a comprehensive picture of the pattern of a country's food supply during a specified reference period. The food balance sheet shows for each food item - i.e. each primary commodity and a number of processed commodities potentially available for human consumption - the sources of supply and its utilization. The total quantity of foodstuffs produced in a country added to the total quantity imported and adjusted to any change in stocks that may have occurred since the beginning of the reference period gives the supply available during that period. On the utilization side a distinction is made between the quantities exported, fed to livestock, used for seed, processed for food use and non-food uses, lost during storage and transportation, and food supplies available for human consumption at the retail level, i.e. as the food leaves the retail shop or otherwise enters the household. The per caput supply of each such food item available for human consumption is then obtained by dividing the respective quantity by the related data on the population actually partaking of it. Data on per caput food supplies are expressed in terms of quantity and - by applying appropriate food composition factors for all primary and processed products - also in terms of energy, protein and fat.
Annual food balance sheets tabulated regularly over a period of years will show the trends in the overall national food supply, disclose changes that may have taken place in the types of food consumed, i.e. the pattern of the diet, and reveal the extent to which the food supply of the country as a whole is adequate in relation to nutritional requirements.
By bringing together the larger part of the food and agricultural data in each country, food balance sheets are useful in making a detailed examination and appraisal of the food and agricultural situation in a country. As estimates of national aggregates, they are suitable for estimating the overall shortages and surpluses in a country. They are also useful in developing projections of future food supply needs or the future demand for food, in setting targets for agricultural production and trade and for establishing relationships between national food supplies, famine and malnutrition as well as evaluating national food and nutrition policies. The food balance sheets also provide a sound basis for the policy analysis and decision-making needed to ensure food security. For this reason, international organizations, governments, planners and researchers find them invaluable in determining whether a nation as a whole is moving towards meeting national dietary recommendations. A comparison of the quantities of food available for human consumption with those imported will indicate the extent to which a country depends upon imports (import dependency ratio) to feed itself. The amount of food crops used for feeding livestock in relation to total crop production indicates the degree to which primary food resources are used to produce animal feed which is useful information for analyzing livestock policies or patterns of agriculture. Data on per caput food supplies are an important element for projecting food demand, together with such other elements as income elasticity coefficients, projections of private consumption expenditure and population.
Conceptually, food balance sheets measure the food supply of the population. In reality, they are often unable to match practice with theory and, as a consequence, the statistics are often criticized for not meeting the expectations of data users. Food balance sheets measure food consumption from a food supply perspective. They do not give any indication of the differences that may exist in the diet consumed by different population groups, e.g. people of different socio-economic groups, ecological zones or geographical areas within a country. Neither do they provide information on seasonal variations in the total food supply. To obtain a complete picture, food consumption surveys showing the distribution of the national food supply at various times of the year and among different groups of the population should be conducted. In fact, the two sets of data are complementary. There are commodities for which a production estimate could best be based on estimated consumption as obtained from food consumption surveys. On the other hand, there are commodities for which production, trade and utilization statistics could give a better nationwide consumption estimate than the data derived from food consumption surveys.
Data obtained through household and food consumption surveys are often the preferred source of food consumption estimates for most analysts because they provide more information on food consumption than food balance sheets do. For example, because the surveys collect data from the people who are purchasing and eating the food, they can obtain information on the consumption characteristics of children, elderly people, males, females and on rural compared with urban populations. This type of information is not available from food balance sheets. In the absence of a comprehensive international data set from household surveys, however, the food balance sheets represent the only source of standardized data that permit international comparisons over time.
Food balance sheets are assembled form a variety of sources. The quality of the balance sheets and their coverage vary considerably among countries and commodities. Inaccuracies and errors may be introduced at each stage of a balance sheet's construction. The user of these data must therefore bear in mind their limitations. Ideally, the basic data required for the preparation of food balance sheets should be obtained from the same source. This implies that, firstly, the country should have a comprehensive statistical system which records all current information relating to each component of the food balance sheet (starting from producers to consumers). Secondly, concepts of the information adopted should be those of the food balance sheet concepts. Thirdly, the information available should be consistent, at least with respect to measurement unit and time reference period. In practice, however, such an ideal statistical system does not exist. Even in the few, mainly developed, countries which possess uncommonly sophisticated reporting procedures, the available data do not always meet either the second or third condition. Therefore, in practice, the basic data are necessarily based on a large variety of sources. The main sources commonly used are discussed below.
Production and trade data are part of the ongoing national official statistics. They are based either on direct enquiries or records, or are estimated by Government agencies. Information on stock changes is available from marketing authorities and factories or from farmer stock surveys. Information on industrial uses are obtained from industrial/manufacturing censuses/surveys. Feed and seeding rates are obtained from cost of production surveys or are estimated by the Government agencies concerned. Losses occurring in industrial processing are also obtained from manufacturing surveys.
Since the basic data are obtained from different sources, they are subject to inconsistency. Their concepts are not likely to be the same as the food balance sheet concepts, since they were not primarily planned for that purpose. The time reference period may not be consistent throughout, or there may be some time lag between the available data. Furthermore, the data are often either incomplete or unreliable. Clearly, directly incorporating such data into the food balance sheet framework is almost impossible. Adjustments to the basic data and estimation/imputation of the missing data are necessary in order to maintain a certain degree of consistency, completeness and reliability of the resulting food balance sheets. In some cases, the exercise has to be based also on other external sources.
A conceptual problem frequently arises with respect to coverage/representativeness of the basic data. Production statistics are mostly confined only to commercialized major food crops. Non-commercial or subsistency production (i.e. home produce and food from hunting, fishing and gathering by households for their own consumption) are usually not included. This might be an appreciable part of total production in some countries. Manufacturing surveys may cover only a certain size of industrial establishment. Information on commercial stocks may be available from official or marketing authorities, factories, wholesalers and retailers, but inventories of catering establishments, institutions and households may not be available. Information on waste in industrial processing may be available, but waste/losses during storage, transportation or on quantities intentionally discarded for the purpose of price control or epidemic disease control may not be available. In these cases, even though the basic data are reliable, some adjustments are required to adapt the basic data to food balance sheets concepts/coverage.
The incompleteness and inaccuracy of the basic data tend to be the major problems. Production statistics may not be available for all commodities needed. Even where the statistics are available, they are not always reliable. This may be due to the fact that crop patterns and utilization of some crops in developing countries are sometimes rather complicated, making it difficult to estimate the production. The estimation of production of some crops is further complicated because they are continuously harvested at regular or irregular intervals over a long period of time, e.g. cassava and certain fruits and vegetables. Moreover, for certain crops, the produce is not completely harvested; a portion is held back as a reserve from which to draw if the need arises or even left to rot, e.g. cassava and plantains. Moreover, certain kinds of food may not be covered by food balance sheets because they are not included in national production statistics. Meat, such as that of game, wild animals and insects, may be excluded for this reason. Under conditions such as those prevailing in many developing countries, this meat may form a substantial part of the low consumption level of animal protein. Also, major food crops may not be grown in pure stands but mix-planted in fields of bewildering complexity. The reliability of official production data may also be questionable. This is because farmers frequently equate production with tax collection and, in some cases, because reliable information on pre-harvest food grain losses caused by pests and diseases are not usually available. Hence, the estimates of yield are likely to be inaccurate; if so, it follows that production statistics derived from the harvested area and the estimated yield may be subject to a biased estimation.
Import and export data may be accurate in the majority of countries, but in some countries there may be significant amounts of trade across national boundaries that go unrecorded. Moreover, import and export transactions may not receive equal attention from the custom's administration because taxes or quantitative controls are generally concentrated more on import items than export. As a consequence, the reliability of export data may also be questionable.
The availability of basic data on the feed, seed and industrial/manufacture use components are rather limited. Seeding rates for crops are fairly well established in most countries, but when the quantities fed to animals have to be estimated, many aspects must be considered. Feeding practices vary from country to country according to the quantity and quality of pastures, the degree to which rearing is intensive, the prices of feedstuffs, etc. In addition, the quality of grain and other feedstuffs fed to livestock may vary from one year to the next. Cost of production surveys and manufacturing surveys, which are the appropriate sources of such data, have not been conducted regularly in most developing countries. Even where surveys are conducted, their coverage is usually limited (e.g. cost of production surveys cover only a few major crops or do not cover livestock commodities, etc.). Moreover, information on stock changes and losses/waste are often nearly non-existent or, at best, only fractional in its coverage, e.g. commercial stocks of some commodities may occasionally be available from official sources or marketing authorities.
The estimate of the total population is also a part of the set of ongoing official statistics. The per caput figure of each food commodity is obtained by dividing the figure for food available for human consumption by the total population partaking of it during the reference period, i.e. refers to de facto population. However, for many countries, this figure may also be subject to either incomplete or unreliable data. The total population estimates may refer to resident population only, i.e. refers to de jure population. Thus, non-resident population, such as illegal immigrants, tourists, refugees, foreign diplomatic personnel and their dependents, foreign armed forces, etc., are not included. This omission may constitute a considerable part in some countries. This, therefore, would understate the total partaker population.
There are also problems related to the time-reference period to be used in preparing food balance sheets. Several twelve-month periods, such as July/June, October/September, April/March, have been proposed and were indeed also applied. However, none of these periods satisfactorily and uniformly covered the production of all agricultural commodities, their trade and domestic utilization. It can be assumed that there is no single twelve-month period which is fully suitable for recording supply and utilization for all products. It was therefore felt that, although the calendar year time-reference period (January-December) might not be a completely satisfactory solution, its advantage would appear to outweigh its disadvantages. The application of a calendar year time-reference period during which the bulk of the harvest takes place also helps in linking the agricultural statistics with those of the industrial and other sectors of the economy.
The accuracy of food balance sheets, which are in essence derived statistics, is, of course, dependent on the reliability of the underlying basic statistics of population, supply and utilization of foods and of their nutritive value. These vary a great deal both in terms of coverage as well as in accuracy. In fact, there are many gaps, particularly in the statistics of utilization for non-food purposes, such as feed, seed and manufacture, as well as in those of farm, commercial and even government stocks. To overcome the former difficulty, estimates can be prepared while the effect of the absence of statistics on stocks is considered to be reduced by preparing the food balance sheets as an average for a three-year period. But even the production and trade statistics on which the accuracy of food balance sheets depends most are, in many cases, subject to improvement through the organization of appropriate statistical field surveys. Furthermore, there are very few surveys on which to base sound figures for waste. In some cases, these estimates are subject to significant margins of error. Typically, assumptions about losses are based on expert opinion obtained in a country. Identification of major gaps in the available data might also stimulate the improvement of national statistics at the source.
Quality assurance is a series of processes to ensure that all information collected and published is reliable. The components of food balance sheets are complex transformations of data from a large number of sources based on sample surveys, censuses, administrative records and best estimates, and this complicates the task of assuring quality. The quality of data varies from one source to another and, in many cases, it has not been evaluated. The transformations themselves and the conversion factors used to estimate processed products and the nutritive content of the foods also influence data quality and complicate the task of quality assurance.
The usual approach to quality assurance is to integrate all the statistical information, the underlying concepts, definitions and methods in order to verify them through a series of vigorous consistency checks and comparisons to other related supplementary information. Consistency, however, is no guarantee of quality since consistent data is not necessarily accurate. One of the most valuable data verification techniques for appraising the quality of balance sheets is the unsophisticated method of comparing statistical aggregates against all available supplementary information.
Once estimates of the other components of the domestic supply have been made, the estimate of food available for human consumption is usually derived as a residual. Since the estimate of food available for human consumption is derived as a residual, its reliability would depend on the availability and accuracy of the other components on which it is based. In the case where the majority of the basic data are available and reliable, and the adjustments are based on sound judgement, the estimate of the food available for human consumption is likely to be reliable.
It stands to reason that where the basic data are incomplete and unreliable, an estimate of food available for human consumption is unlikely to be accurate. Furthermore, since it is derived as a residual, the error is not quantifiable and its direction is also unknown. In view of the frequent use of the estimate of food available for human consumption in various food and nutritional studies, it would be desirable if a more reliable and justifiable estimate of this component could be made available. At a minimum, this means the quantity of food available for human consumption would have to be estimated independently based on other existing statistical sources of information. One such source would be a household survey which collects quantities of food items consumed or acquired. Consideration of the survey data as the basic statistics pertaining to the food availability element does not, of course, necessarily imply using them directly as the estimates of food availability. They should rather be used as inputs or starting points in a process of adjustments that will have to take into account conceptual differences, judgements regarding data quality and also the consistency in relation to the inputs or estimates for the other elements of the food balance sheet. The use of the survey data in this manner should help to reduce the reliance on the residual or balancing approach in arriving at the food availability estimates, while also allowing more flexibility in handling the other elements for which the basic statistics are poor.
Nevertheless, food balance sheets, while often far from satisfactory in the proper statistical sense, do provide an approximate picture of the overall food situation in a country and can be useful for economic and nutritional studies, for preparing development plans and for formulating related projects.