Deborah Foote is Deputy Chief Dietitian, Royal Alexandra Hospital for Children, Camperdown, NSW 2050.
An important tool in the repertoire of the clinical dietitian is familiarity with the ingredients and nutrient composition of a wide variety of commonly eaten foods. Formal use of food composition data is made in several ways in the clinical dietetic setting.
Assessment of nutrient intakes
Nutrient intakes of an individual are most commonly assessed from a dietary history or weighed food diary. Using the dietary history method the dietitian questions the subject on his or her usual eating patterns including types and amounts of foods and liquids consumed, and the frequency of consumption of the foods eaten. A dietary history will include an indication of the variation in intake from day to day and of the range of foods typically eaten at each meal or snack time. The dietitian will make estimates of the amounts of food consumed. The food composition tables would then be used to calculate the nutrients obtained from a typical day's intake. These results would only be a guide to the subject's usual intake, being based on so many estimates.
Using the weighed food diary method the subject (or caregiver) weighs or measures, using metric cups and spoons, all food and liquids actually consumed over a period of three or four days. This gives much more accurate amounts than a dietary history, however, there may be some problems. Subjects may alter their usual eating patterns to make the recording easier, or may omit to weigh or record some foods consumed or may not describe foods adequately. A weighed food diary should be done over some weekdays and some weekend days to cover the possible variations between these periods. Nutrient intakes are calculated from the records of foods consumed over the period of the diary then averaged to give daily intakes.
Results from the calculations of nutrient intakes from either a dietary history or a weighed food diary would be compared to the recommended dietary intakes (RDIs) for Australians in the appropriate sex and age group for the subject (National Health & Medical Research Council 1986).
Advice may be given to the subject regarding desirable changes to the diet, based on results of the assessment. If there appears to be a trend to low or excessively high intake of any nutrients such advice may be given, however the dietitian needs to be very cautious in making judgements based on such calculations.
Planning special diets
Most special diets involve controlling the amounts of certain foods eaten according to the relevant nutrients for the medical condition being treated. Reduced or increased intakes of nutrients may be needed. Food composition data allow dietitians to formulate exchange lists giving allowable serving sizes of interchangeable foods, or allowed and disallowed food lists for use in special diets. These lists may be based on different nutrients: carbohydrate for diabetic diets, protein for renal diets, sodium for renal or cardiac diets, potassium or phosphate for renal diets, particular amino acids for metabolic disorders, eg phenylketonuria (PKU) and so on for a large number of conditions.
Commercial food lists
In conjunction with diet sheets which list basic foods that are allowed or disallowed on special diets, dietitians will frequently supply commercial food lists. Both nutrient and ingredient composition data of manufactured foods are used to collate lists of foods by brand name which can be included in various special diets. Data are used either to calculate appropriate serving sizes of commercial foods to be used with exchange lists eg diabetic and PKU diets, or to determine allowable foods on diets eliminating particular ingredients, eg gluten- and wheat-free, milk- or egg-free, sucrose-free diets.
Another use of food composition data is in analysing recipes. These calculations can be used either for food items which are to be included on a hospital menu or in cookbooks to be supplied to patients on various special diets. Nutrients in each of the ingredients in a recipe are summed and the average content per serving is calculated.
Assessment of nutritional adequacy of hospital menus
In many hospitals, the cycle menu is planned by the food service manager who would frequently ask the dietitian to review the menu for its nutritional adequacy. The dietitian would look for compliance with the Australians dietary guidelines (Commonwealth Department of Health 1981) and may also calculate possible nutrient intakes from various combinations of food choices from the menu. It would be assumed that full meals would be chosen and consumed.
Problems using the Composition of foods, Australia
The Composition of foods, Australia (Cashel & others 1989) has been released with data for only some of the food groups from new Australian analyses. The new tables still include at the back many foods remaining from the old tables (Thomas & Corden 1977) for which the nutrient composition data are from foreign sources. The dietitian must remember that in different countries the same food name can be given to very different foods which would have widely variable nutrient composition, or the same foods have different names. It is important to keep in mind the variability of many local foods when analysing an individual's dietary intake. Nowadays many dietitians use computerised nutrient analysis of packages frequently based on NUTTAB (Commonwealth Department of Community Services & Health 1988). The information included in this computer data base is not as extensive as in the printed tables and therefore has more limitations in its use.
From a paediatric dietitian's point of view the main difficulty is the lack of compositional data on many of the foods commonly consumed by children eg baby foods, both commercial and home prepared, and infant formulas are still not included. Some food groups still have only a very limited range of individual foods in the tables, eg breakfast cereals, biscuits, confectionery, ice creams, compared with the enormous range available commercially.
Abuses of food composition data
Use of food composition tables by inexperienced unsuitably trained people eg health workers with little or no training in nutrition and food skills, leads to taking imprecise diet histories or food records and then attempting to calculate detailed nutrient intakes from this sketchy information. Such people will frequently be unable to make correct or best choice of the most similar food when a consumed food is not listed in the food tables. Their knowledge of food and nutrients may not be sufficient to know how alike various foods are in nutrient composition or which are the most important nutrients to access in different situations.
Any practitioner (adequately trained or not) can be guilty of making unjustifiably strong judgements based on calculations from a diet history or measured food intake over a small number of days. Both methods of determining food intake are notoriously open to inaccuracies. Accurate assessment of food intake over long periods is necessary before a really definite statement can be made that a diet is inadequate. Nutrient deficiencies can really only be diagnosed in the presence of corroborating biochemical and clinical evidence.
Knowledge of the nutrient composition of foods forms the backbone of clinical therapeutic dietetics. Without access to such data dietitians would be unable to assess patients' nutrient intakes adequately or to give individualised dietary instructions which patients can follow on a long term basis.
Cashel, K, English, R & Lewis, J. 1989. Composition of foods, Australia. Canberra: AGPS.
Commonwealth Department of Community Services & Health. 1988. NUTTAB88. Nutrient data table for use in Australia. Disk or tape format. Canberra: Commonwealth Department of Community Services & Health.
Commonwealth Department of Health. 1981. Dietary guidelines for Australians. J. Food Nutr. 38: 111–9.
National Health & Medical Research Council. 1986. Recommended dietary intakes for use in Australia. Canberra: AGPS.
Thomas, S & Corden, M. 1977. Metric tables of composition of Australian foods. Canberra: AGPS.