Frequently asked questions (FAQ)

How to use the FAQ
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Where can I find information on the nutrient composition of South African food?
Information on the nutrient composition of South African foods is available from the South African Food Database (SAFOOD). The data can be accessed in the following ways:
  1. printed food composition tables and in the
  2. software programs.    
Where can I get the information on the reference for a specific nutrient?
The reference source for each nutrient of a food is recorded in the reference database of the South African Food Database System (SAFOODS).  Please contact us for the relevant information.
  
Are all the values in SAFOOD of South African origin?

No, not all the values are of South African origin. Read more.   

How is the energy value of the food calculated?

The metabolisable energy value of a food item was derived by multiplying the amounts of protein, total carbohydrate (available carbohydrate plus dietary fibre) total fat, and alcohol (when applicable) with the conversion factors shown below. The results are tallied to give the energy value of the food item.

1 g protein = 17 kilojoules (kJ) or 4 kilocalories (kcal)
1 g total carbohydrate (available carbohydrate plus dietary fibre) = 17 kJ or 4 kcal
1 g fat = 37 kJ or 9 kcal
1 g alcohol = 29 kJ or 7 kcal   

Why don’t the proximate values (moisture, ash, carbohydrate, fibre, total fat, protein) always add up to 100?

Each of the analytical methods used for the individual proximates has an acceptable degree of variation from the true value. If, for example, the proximates are at the upper-end of their acceptable range, the sum of the proximates will be more than 100 g (and vice versa).

The rounding off of reported values adds to the compounding error of a value. Another possible reason is that organic acids and non-nutrient factors, which also contribute to the weight of the food, may not be included. The range of 97-103 g for the sum of the proximates could be considered acceptable (Greenfield and Southgate, 2003). Values falling outside this range were evaluated for valid reasons for the discrepancy.   

What is the difference between total carbohydrate and available carbohydrate?

Total carbohydrate is the sum of available carbohydrate plus dietary fibre while available carbohydrate include sugars that are glycogenic and polysaccharides hydrolysed in the digestive tract of humans (Greenfield and Southgate, 2003).   

Why don’t the fatty acid fractions (SFA, MUFA, PUFA) add up to the total fat value?
In most foods ‘total fat’ (total lipids) is made up of fatty acids plus non-fatty acid material such as glycerol, phosphate moiety of phospholipids and sterols. To calculate what proportion of the ‘total fat’ content in 100 g of a specific food item is fatty acids, fatty acid conversion factors can be used. The fatty acid conversion factors for different foods are: (a) Milk and milk products, 0.945; (b) Eggs, 0.830; (c) Meat and meat products, 0.910-0.945 (organ meats: 0.561-0.789) (Holland et al., 1991).

Fatty acid conversion factors for fruit and vegetables range from 0.534-0.950 g fatty acids/g of total fat (US Department of Agriculture, 1998).

I can’t find a food item I am looking for – what should I do?

If you have trouble finding a food item in the online database try to enter the name in a different format, e.g. if you cannot find brown bread, try bread, brown. As there are so many food items on the market there is a possibility that the food item that you are looking for may not be in SAFOOD. If you feel there is a food item which is regularly consumed by a large part of the South African population you are working with, you are welcome to register that food item by sending an email to safoods@mrc.ac.za. This could assist the SAFOOD compilers to identify the food items that should be included in the database.   

Do foods in the South African Food Database have salt added?

Unless otherwise specified, there is no salt added to the foods in the South African Food Database. Recipe foods (calculated) also do not have salt as an ingredient. The exception is processed foods (e.g. canned vegetables, polony, etc.) where the sodium and chloride values reflect the salt added during processing.   

How do I know if a canned product’s nutrient values (e.g. canned meat) reflect only drained solids (meat only) or the whole can contents (meat and brine)?

Usually the total contents of a canned product are analysed since it is a requirement for labelling purposes. Since food analysis is expensive, most manufacturers do not analyse the drained solids separately. In the South African Food Database the canned foods represent data on the analysis of total can contents. Where data on only drained solids were available, the canned food has “drained solids” indicated in parenthesis in the food name.

Why is the vitamin and mineral composition of processed foods sometimes higher than that of the raw food?

Conclusions cannot be drawn from the direct comparison between the vitamin and mineral composition of different forms of a specific food (raw, boiled, frozen, canned, etc.). The destruction of some nutrients by heat is only one of the factors influencing nutrient composition during processing. Moisture loss during cooking leads to the concentration of all nutrients. In addition, most often it is not samples of food from the same crop that were analysed raw, frozen, boiled, canned or dried. Differences in growing conditions, sample handling, etc. could therefore result in nutrient differences. Analyses for the various forms (raw, boiled, frozen, canned, etc.) of a food item may also have been done at different analytical laboratories, possibly using different analytical methodologies and thus producing different values. With inter-laboratory studies the impact on values, using different analytical methods, can be minimised. Adding additional ingredients to processed food as well as the fortification of the food item may also influence the final analytical values.

What does a “zero” or “trace” value mean?

Analytical methodology for nutrients are continually improving and becoming more accurate. A zero value was used when it is known that the specific nutrient is normally not present in that food.

The term trace value (“tr”) means that the nutrient is present in that food, but at such low levels that it cannot be adequately measured. A trace value can also be regarded as nutritionally insignificant as it is too small to be expressed in the unit of measurement used in the specific food database (Greenfield and Southgate, 2003).   

How do missing values affect the interpretation of analysed dietary intake data?

As a user of food composition data, you need to be aware of missing values in the food composition database. Missing values should not be regarded as a zero value. A missing value means that no information is yet available for the nutrient. When analysing dietary intake data, missing values should be flagged or the results interpreted keeping in mind that missing values lead to an underestimation of nutrient intake of an individual or population.

In order to reduce the number of missing values in a food composition database it is practice to estimate values by using other reference sources or by deducing the values from related foods. Estimated values prepared by careful interpretation of the data on related foods are acceptable in nutritional studies, provided that their use is clearly noted.   

What are the limitations of food composition data?

a.   Limited coverage of foods
It is unlikely that a database can ever be complete. This is due to the great number of foods on the market and the continuous addition of new products. The high cost of analysis also influences the availability of nutrient information on foods. Foods to be included in a country’s database are therefore prioritised based on the dietary intake patterns of the specific population. Data on the dietary intake patterns of the South African population served as a guideline for including food items in SAFOODS.

An attempt was made to include data on all major food products and generic foods. The South African Food Database contains information on most of the commonly consumed food items in South Africa.

b.   Limited coverage of nutrients
The high cost of food analysis and high level of instrumentation and analytical skills needed, contribute to the limited number of nutrients included in a database. It is common to find incomplete coverage of nutrients even if nutrient values are borrowed from other countries’ databases. The nutrients covered also reflect the change in nutritional interests with time.

Priorities were set for recording of specific nutrients in the South African Food Database according to the needs expressed by users.

c. Nutrient variability
Information on factors that influence nutrient variability in vegetables, fruit, milk and milk products, eggs, meat and meat products can be found in the Supplements to the 1991 FCT (Kruger et al., 1998; Sayed et al., 1999).

How do I quantify food intake in household/metric measures when the food composition tables express the nutrient values per 100 g of food?

A useful tool is the MRC Food Quantities Manual, which has the weight of foods in common units and household measures for many of the foods listed in the FCT.

How do I estimate the nutrient values for a food item (based on a recipe) not in the tables?

Guidelines on how to use a recipe calculation to estimate the nutrient content of a food item is given in the Recipe Calculations section of the printed FCT.

Can I use the food composition data in another product (book, computer product, etc)?

Before any part of the South African Food Database can be reproduced, permission must be granted by the Medical Research Council (MRC) in writing. Even if the use of the reproduced copy is for educational purposes, written permission from the MRC is still required.

Written requests can be forwarded to
 safoods@mrc.ac.za