The diet history aims to discover the usual food intake pattern of individuals over a relatively long period of time. It is an interview method composed of two parts. The first part establishes the overall eating pattern and includes a 24hr recall: questions such as "What did you have for breakfast yesterday?" coupled with "What do you usually have for breakfast?", following through the entire day in this way. Subjects are asked to estimate portion sizes in household measures with the aid of standard spoons and cups, food photographs or food models. The second part is known as the "cross-check". This is a detailed list of foods that are checked with the subject. Questions concerning food preferences, purchasing and the use of each food serve to verify and clarify information given in the first part. Questions about purchasing can also provide a check on portion estimates.

The diet history has advantages over other methods in that it estimates nutrient intakes over a long period of time. Its disadvantages are that it takes about one hour of careful questioning and the interviewer must be a nutritionist or dietitian experienced in obtaining diet histories. The most common fault of an inexperienced interviewer is probably that of suggesting answers. An additional problem is that there is a learning process for the subjects - people become more able to provide information about their food intake with practice. Occasionally this may mean that the first diet history has to be discarded.