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Week-weighted Averages in CANDAT

When expressing and comparing results of multi-day (3 day commonly) food recalls one tends to use the average daily intake as a measure of a subject’s intake. Of course, 7 day recalls will give more accurate estimates of this daily intake and the accuracy will increase if all the days of a week are used. The assumption here is that subjects will eat differently on different days with the greatest variability been between week days and weekend days.

Rather than simply computing an average daily intake one may get more accurate results by weighting the days of the week and the weekend days differently.

A weight of 5 for each week day and a weight of 2 for weekend days should allow us to calculate week-weighted averages for any number of recalls. Of course, for recalls without weekends this would just be a day of the week average and vice-versa.

The week-weighted average could be calculated as follows:

xw = (∑ wi × xi) ÷ ∑ w

where xw is the weighted average with  xi as the daily intakes, and i is 1 – 5 (codes for days of the week) or 0,6 codes for weekend days corresponding to Sunday and Saturday respectively. w1-5 would then be 5 and w0,6 would be 2.

with a variance of

Var(xw) = Var(x) × ((∑ wi2) ÷ (wi)2)

where Var(x) would be the variance over all the days of the food intakes for the subject.

Recommended intakes

This is an area that has changed over the years. The ultimate flexibility requires that one be able to set levels by age and sex, by activity level and by pregnancy status. These levels can then be used to report on the adequacy of an individuals nutrient intake. Scores can then be given for individuals and average scores then derived for populations under study.

Food Groups in CANDAT

Candat has a sophisticated food group analysis function. Food groups are lists of foods which belong to a specific group. These lists are defined as individual food codes or ranges of food codes. Definitions of multiple food groups taken together are stored in what Candat calls a “Category” file. It is thus possible to have category files for many different kinds of food groupings. For instance you could have a category file for groupings of interest to diabetic subjects or particular kinds of cancer subjects or heart disease subjects. There is no limit to the kinds of category files that you can define and, once defined, can use in all your studies.

Nutrient data calculations

Food consumption research calculations are quite simple. Take the food eaten, say eggs, take a quantity, say 2 eggs and multiply the nutrient concentration needed, say protein, by the quantity (2) and you have the protein contribution by eggs. Simple… not so.

Nutrient databases express nutrient concentrations per 100 G. How many 100 Gs in one egg? Fortunately most nutrient databases also have food factors, in this case, small egg, average egg, large egg, etc. Each one of those has a factor. For instance if your egg is 60 G then your factor should be .6. The factor has to be .6 because that is what you multiply 100 G by to get 60 G. Hence all the of nutrient concentrations have to be multiplied by this same factor to yield the proper nutrient contribution. The protein for eggs in this case would be 2 (eggs) x .6 (factor) x [protein]. The square brackets around the nutrient denote concentration per 100 G. Simple? Of course it is.

Nutrients

Associated with each food is a series of nutrients. In food consumption research, these are the interesting values. Nutrients in foods are what affect the body eating them. Energy, muscles, well-being, diseases, sickness, all are affected by nutrients. Food research helps find the links between nutrients and their effects and thus which foods should be eaten or avoided.

Studies have to be carefully crafted to take into account the sources of food information as well as other factors which may be having an effect such as obesity, activity, smoking, alcohol consumption (which is just another food), etc.

Food data

All food databases store nutrient concentrations per 100 G weight of the food. For foods that are typically used by volume measures one must also know the density of the food, ie. how many G are in 100 mL in order to be able to figure out the weight of the food actually consumed. Food databases usually include conversion factors which allow the calculation of density. For instance if a food factor is given for a cup and we assume a cup to be 250 mL then we can calculate the density. Density of a food also depends on how it is served. A cupped of diced vs a cup of crushed pineapple. Each one of these would have a different density.

In scientific studies with multiple coders of food data it is important to ensure consistency. When a subject mentions pasta as a consumed food, which, of multiple pasta codes must the coder use? Is more information required? A user manual which documents the decisions made during coding is essential. Coder training in the use of the manual is also essential.

The more accurate and consistent is the data coding and entry the more valuable will be the resulting data and the more likely will the study be able to show nutrient effects.

Food databases

This section will describe food databases and their characteristics. All research must document the methods used in arriving at their conclusions. Food databases are sources of information used in food research. They change! Every few years new databases are released.

A good source of food information is essential for research. Fortunately many countries already provide access to databases of food information and today’s software uses that information.

It is important for you to be able to manage this food information on a food by food basis. You may need foods that are not already provided and so need to add them to the database. Some foods may have information you consider inaccurate, you must be able to edit these foods. There is a lot of information available to you in these databases, you must be able to access this information easily and efficiently.

As an introduction to this exciting field we are making available, for free, a food profile utility based on the most recent Canadian food file data. This utility is taken directly from CANDAT. It allows you choose the food you want and to view the nutrient information for different servings. Try it for free by downloading it and installing it on your PC.

The sidebar from this site contains information about food intake research. We also have software which allows food manufacturers to calculate the nutrient values of their foods. This software is presently being used by a large international food manufacturer as a tool to manage the nutrient information of their raw materials and finished products.  If you need information about nutrient declarations and food labeling, please contact us directly using this link. Contact Us

Please continue to view the information on this website, download and use our free utility and feel free to contact us for any information.

Have a look at all the food data available world-wide. Follow the links to Food composition tables for more information.

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