|  | Situation 1 This would attenuate the association between n-3 fatty acid intake and the risk of colon cancer. So the association found in the epidemiological study is weaker than the ‘true’ underlying association. It could be the case that this epidemiological study will not pick up the effect of n-3 fatty acids on colon cancer. |  |

|  | Situation 2 The epidemiological study would still find an effect of n-3 fatty acid intake on colon cancer. However, if the values for n-3 fatty acids in the database are consequently above the true value, nutrient recommendations with respect to n-3 fatty acids intake and the risk of colon cancer based on those results would be too high. If the n-3 fatty acids data in the database are systematically below the true values, the recommendations would be too low. |  |

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The following examples illustrate why insight into the quality of the data in a FCDB is important.

Example 1: (epidemiological) research.

Imagine the following research project

- An epidemiological (case control study) to the relation of n-3 fatty acids and colorectal cancer.

- Past food intake is assessed by a food frequency questionnaire (FFQ).

- Food composition data are used to calculate n-3 fatty acid intake.

Consider the following situations

Situation 1

The food composition data with respect to n-3 fatty acids are not very precise. How would this effect the outcome of this epidemiological study? Show answer

Situation 2

The food composition data with respect to n-3 fatty acids are not very accurate. For example the reported values are systematically above the true value. What would happen if the outcomes of this epidemiological study are used to give recommendations regarding n-3 intake to the population? Show answer

Therefore, to get valid results from epidemiological research, high quality food composition data are important. At least, it is important to have information on the quality of food composition data (e.g. their validity and precision) in order to interpret results from epidemiological research.