A dietary survey is a consumer profile charting diet against such factors as age, gender, and income — the systematic study of what a population eats and how it varies. National surveys sample thousands of households or individuals, combining dietary recalls or food diaries with measurements of height, weight, blood pressure, and blood nutrient levels. The resulting picture shows who eats what, who falls short of which nutrients, and how diet tracks with social class, region, and ethnicity. Governments use the findings to set fortification policy, target interventions, and monitor whether dietary guidelines are reaching anyone; industry uses them to spot market gaps. The great national surveys — America’s NHANES, Britain’s NDNS — run for decades, creating the time series that reveal how a nation’s diet is changing and what it is costing in health.