Development and validation of the SAGA Food Frequency Questionnaire with Focus on Fish Consumption
This study validates the SAGA Food Frequency Questionnaire for use in Nordic adult populations, demonstrating favorable reproducibility and a significant correlation between reported fish consumption and plasma long-chain n-3 fatty acid levels.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Diet is one of the most powerful forces shaping human health, influencing everything from the risk of chronic disease to how many years a person lives in good health. Yet, what people eat varies wildly depending on where they live, their age, their income, and the season. In Iceland, the national diet has a distinct character, defined by a high intake of fish, particularly lean varieties, and a common habit of taking fish oil supplements. To understand how this specific diet affects health over time, scientists need a way to ask large groups of people what they usually eat without overwhelming them. The standard tool for this is a food frequency questionnaire, a survey that asks how often someone consumes specific foods over the past year. While these surveys are efficient for large studies, they are only useful if they actually capture what people eat. If the questions are unclear or the answers don't match reality, the entire study could lead researchers down the wrong path.
A team of researchers from the University of Iceland and Chalmers University of Technology set out to test the reliability of a specific questionnaire designed for the Icelandic Stress-and-Gene-Analysis cohort, known as the SAGA study. Their goal was to see if this tool could accurately measure dietary habits, with a special focus on fish consumption, which is central to the Nordic diet. They began with a pilot study involving 922 adults who filled out an electronic version of the questionnaire and provided a blood sample. From this group, they selected a smaller, random sample of 200 people to participate in a deeper validation process. These participants were asked to fill out the same questionnaire again, roughly a year and a half later, to see if their answers remained consistent over time. To check if the questionnaire matched actual eating habits, a subset of these participants also kept a detailed four-day food diary, writing down everything they ate and drank, including portion sizes and cooking methods. Finally, the researchers used the blood samples taken during the initial pilot study to measure the levels of long-chain omega-3 fatty acids in the participants' plasma, a biological marker that reflects recent fish and supplement intake.
The results showed that the questionnaire was a robust tool for capturing the dietary habits of Icelandic adults. When the researchers compared the first questionnaire with the second one, the answers were remarkably consistent for most food items. Out of 78 different food variables, 75 showed a moderate to strong agreement, meaning the survey successfully captured the general pattern of what people ate, even after a significant time gap. The consistency was particularly high for fish. Whether participants reported eating lean fish, fatty fish, or taking fish oil supplements, their answers on the two separate occasions aligned well. This suggests that the questions were clear and that people could reliably recall their usual eating habits over the past year. The researchers found that 78 percent of the participants ate fish at least once a week, and 61 percent reported taking fish oil supplements, highlighting how deeply embedded these foods are in the local culture.
To ensure the questionnaire wasn't just consistent with itself but also accurate, the team compared the second questionnaire against the detailed four-day food diaries. This comparison revealed a positive link between the two methods, especially for foods that people eat regularly. For the most common food items, the questionnaire successfully ranked people according to how much they ate. While the agreement was not perfect for every single item—infrequently eaten foods like sushi or certain types of meat were harder to capture accurately—the overall picture was clear. The questionnaire worked best when grouping similar foods together, such as combining different types of bread or vegetables, rather than trying to pin down the exact frequency of every single variation. This approach helped smooth out small errors and provided a clearer view of overall dietary intake.
Perhaps the most compelling evidence came from the biological data. The researchers looked at the levels of long-chain omega-3 fatty acids in the participants' blood and compared them to how much fish the participants said they ate on the questionnaire. They found a significant connection: those who reported eating more fish had higher levels of these beneficial fats in their blood. This link held true even when the researchers separated the data to account for people who took fish oil supplements. The fact that the self-reported answers matched the biological reality in the blood confirmed that the questionnaire was not just a collection of guesses, but a valid measure of actual nutrient intake. The study concluded that this specific food frequency questionnaire is a reliable instrument for assessing diet in the Nordic region, capable of accurately ranking adults by their food intake. This validation is crucial for future research, as it ensures that scientists studying the complex relationship between genetics, stress, and health in Iceland can trust the dietary data they are collecting.
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