Background
It is not possible to generate a nutrient profile for every food consumed during a National Nutrition Survey using only analytical data, because of the variety of ways people prepare food. In this situation Food Standards Australia New Zealand (FSANZ) relies on recipe calculations to generate nutrient data for foods and beverages consumed.
In addition to selecting the appropriate ingredients and proportions for each recipe, certain factors must also be applied to account for changes to a food or beverage as a result of preparation or cooking.
The weight change factor accounts for how much moisture a food will lose or gain during cooking. The majority of foods will lose moisture as a result of cooking, and the amount of loss will vary according to the cooking method. A smaller number of foods, such as dry pasta and rice, will gain moisture during cooking. The loss or gain of water during cooking can have a dramatic effect on the nutrient content of a food when expressed on a per 100 g basis.
The retention factor adjusts the level of each vitamin or mineral in an ingredient as a result of the preparation and cooking process undertaken. Each method of cooking, and the time for which the food is cooked, may affect individual nutrients to different extents. For example, water soluble vitamins may leach out into the water during boiling, which will reduce the level in the food, while mineral content may remain unchanged.
To ensure the recipes developed for the 2011-13 Australian Health Survey (AHS) drew on the most up to date factors available, FSANZ conducted a review of the recipe factors in FSANZ current databases and the current scientific literature to determine whether more suitable factors were available.
Review process
The review of retention factors and weight change factors for use in recipe calculations for the AHS were undertaken following the key steps outlined below.
Review of FSANZ existing recipe factor databases
The retention factors in FSANZ's original database were based on the retention factors published by the United States Department of Agriculture (USDA) Table of Nutrient Retention Factors Version 5 (2003), with some factors also based on published literature (e.g. the retention factors for fat and oil, cooked). The original database did not contain retention factors for all nutrients to be reported as part of the AHS. For example, retention factors were missing for iodine, selenium and vitamins B6 and B12.
The weight change factors in FSANZ's original database were based on the weight change factors used in the 1995 National Nutrition Survey (NNS). FSANZ has verified some of these factors in the past, using analysed values for similar foods, or by weighing foods before and after cooking. Some common cooking practices have changed since the 1995 NNS. For example, more people are now cooking their food using a microwave.
FSANZ reviewed and updated both recipe factor databases as part of the development of AUSNUT 2007 for estimating food and nutrient intakes from the 2007 Australian National Children's Nutrition and Physical Activity Survey (ANCNPAS). Due to the length of time between surveys, FSANZ decided to conduct another review of the current literature to ensure that the AHS databases were as complete and accurate as possible.
Review of current scientific literature
FSANZ undertook an extensive review of the current literature to compare weight change factors and retention factors from around the world with our existing data. Sources of new information included international databases, Australian industry data and scientific literature. In addition to the factors themselves, information was gathered for all aspects of the recipe ingredients and preparation practices including specific meat cuts, peeling of vegetables, cooking time, temperature and method, portion size, etc. This information enabled comparison of factors that were most appropriate for Australian practices.
Incorporating new factors into FSANZ recipe factor databases
The factors found as a result of the literature review supported the values in FSANZ's existing retention factor and weight change factor databases. Therefore updates focussed on filling missing values, for nutrients not previously reported and confirming weight change factors for newer cooking methods.
Retention factors
FSANZ used a range of sources for filling the nutrient retention factor gaps identified as part of the review of the original database. For example, the retention factors for:
- Iodine were estimated using Australian derived analytical data for a variety of raw and cooked foods including fish, chicken, potato and egg.
- Selenium were imputed from values for zinc based on the findings in two papers; one analysing the retention of selenium in potatoes and the other in pork. Both reports indicated that the retention behaviour of selenium was similar to that of zinc in these commonly consumed matrices.
- Vitamins B6 and B12 were either borrowed from the USDA (2007), or averaged using the USDA data and data published in Bognár (2002).
Because the literature indicated that there was no consistent effect of microwaving on nutrient retention compared to other traditional cooking methods such as steaming or boiling, new retention factors were not created.
Weight change factors
FSANZ also used a range of sources for filling the weight change factor gaps identified as part of the review of the original database. For example, the weight change factors for:
- beef and lamb were updated using recent analytical data provided by the meat industry
- cakes, slices, breads and sausages were updated using recent analytical data generated by FSANZ
- mixed dishes were updated using a range of analytical data generated by FSANZ.
FSANZ staff also performed some manual weighing of foods before and after cooking to fill data gaps for weight change factors and to validate existing factors. This was generally targeted at foods which have increased in popularity for Australian consumers, such as pizzas.
Conclusion
Conducting this review provided FSANZ with an improved level of confidence in the recipe factors used to calculate nutrient profiles for foods and beverages reported as consumed during the NNPAS.
References
Bognár, A. (2002). Tables on weight yield of food and retention factors of food constituents for the calculation of nutrient composition of cooked foods (dishes). BFE, Karlsruhe, Germany, p. 7-11; p. 41-43; p. 95-97.
United States Department of Agriculture. (2003). USDA Table of Nutrient Retention Factors, Release 5.
United States Department of Agriculture. (2007). USDA Table of Nutrient Retention Factors, Release 6.