The use of dietary intake assessment and questionnaires in clinical practice is largely debated, particularly for obese patients. The time needed to carry out them is very long, and the results are little or not at all workable due to the underreporting which may represent up to 50% of intakes for some patients. The usual methods and tools to evaluate dietary intakes are presented, they should not be used to calculate energy intake, but they permit to initiate a dialogue with the patient on his/her dietary pattern. The analysis of the dietary pattern is the first step in diet prescription and is essential to weight management and follow-up. This analysis must consider 3 important components: type of food usually eaten and preferred, the circumstances and environment of food intakes and meals, possible disorders of eating behaviour. Some results on food consumption in adults and children from the Fleurbaix Laventie Ville Santé Study are presented.