When conduction nutrition research, it is frequently necessary to find out exactly what the experiment participants are eating. Three of the most common methods for doing so are as follows.
Food Frequency Questionnaires (FFQ)
The participant in the study is asked what types of food they eat and how often. For example, do they eat bread? If so, what type (white, wholemeal etc),?How many slices do they have per serving, and how many times per day and per week do they eat this. Using this data, researchers can estimate how much food and what types a person consumes.
24 Hour Dietary Recall Questionnaire
Similar to the FFQ, this method involves administering a questionnaire to the research participant. In this case the participant is only asked to recall what they have eaten during the last 24 hours. This can be a more accurate method, as the participant only has 24 hours worth of eating to remember, and does not have to factor in foods that they eat occasionally. The flip side to this is that the 24 hours being studied may not be indicative of their usual diet.
The participant is given a diary to fill out with the details of what they eat on an ongoing basis. The food diary may be used for a few days or several months. Diaries tend to be more accurate than FFQ or other questionnaires, however they are not perfect. Users of food diaries often change their eating habits when they know they are being monitored. The motivation to accurately complete the diary can fade over time, leading to less accurate reporting. Diaries also take more time and money to issue, and then analyse.
Each of these methods provide “usable accuracy”, but are far from perfect. Participants may fill out the questionnaires or diaries incorrectly. Or they may deliberately under report certain eating habits. We know that people tend to under report alcohol and unhealthy food intake. Overweight or obese people have been shown to under report total food/calorie intake.
Some researchers have asked participants to take photos of the food they eat. This can provide additional accuracy, but still does not show all ingredients and their quantities in each meal.
With the rise of nutrition apps such as MyFitnessPal, it may become easier for researchers and participants to obtain accurate data at a reasonable cost. Nutrition researchers are actively exploring the role that technology and apps can play in accurate and efficient food intake reporting.
Data from these reporting methods is then turned into nutrient intake data using a food composition table. The macro and micro nutrients, along with other data of each food are listed. These tables are tailored to certain regions or countries. For example, the UK food composition table will list different foods and data than the USA table. This is to take into account which foods grow where in the world, different food treatment, storage processes etc, all of which affect the nutrient content of the food.
The International Network of Food Data Systems website keeps an updated list of many of the food composition tables used around the world.
Once this nutrient intake data is collected and analysed it can be used in a variety of ways. In the next post we will look at different techniques used in nutrition research.