How food consumption data are to be converted to nutrient intakes is an important consideration. Firstly, a nutrient composition must be allocated to each item on the questionnaire. This could be either a single food or average of several foods. For example, if the question is about "beef", which cut of beef is used? Should nutrient values for "lean only" or "lean plus fat" be used? If nutrient values for several foods are to be used for one item on the questionnaire, should average nutrition values be taken for these, or should the nutrient composition values be weighted in some way? The most appropriate food(s) and weighting of the nutrient compositions will be dependent upon the dietary habits of the population being studied.

The nutrient composition used for an item could be modified depending upon the answer to another question. In the beef example above, if subjects are asked whether they usually eat the fat on meat, the composition of "lean+fat" cuts could be used for those who answer "yes" and the composition of "lean only" cuts could be used for those who answer "no". The nutrient composition used for items such as fried foods or home made cakes and pastries could be modified depending upon the answers to other questions about the type and brand of fat used. For each item on the questionnaire, the frequency of consumption is multiplied by the portion weight to yield a weight of each foodstuff consumed per week. This is then used with the nutrient composition of the item to calculate the mean daily nutrient intakes.