Insights into Self-Reported Dietary Intake
The value of dietary intake questionnaires to estimate food intake is under debate. A systematic review of 45 dietary intake studies conducted with children aged 6 to 12y finds timing of the interview to be important. As the interval between food consumption and the dietary intake survey increased, accuracy of recall diminished. Children’s age, body mass index, social desirability, food preferences, and cognitive ability were also related to accuracy.
Among adults, self-reported intake measures have been found to systematically underestimate energy intake by hundreds of calories daily. The severity of underreporting varies by body weight (obese individuals are more likely to underreport) and food type (snack foods are more likely to be omitted). One contributor is that incorrect identification of the food which was consumed. To be accurate, the exact food and quantity consumed must be reported.
Because consumer preferences and nutrient content of branded products change with time, self-reported intake cannot be simplified to generalized food categories, e.g. ready-to-eat cereals, pizza, bread, salami, etc. Food and nutrient databases must be continuously updated to reflect a changing marketplace and across the entire spectrum of choices - from individual ingredients used in home food preparation, partially-prepared foods, and away-from-home and restaurant food choices. With hundreds of thousands of food and beverage products in grocery and mass market channels, without mentioning restaurant and food service choices, it is not surprising that consumers have difficulty remembering accurately.
Recall must be coupled with accurate nutrition information for food ingredient/products. This is a huge task. Self-reported measures of dietary intake are so inaccurate that researchers question their value in scientific research to understand actual energy intake and physical activity energy expenditure. Using the classic 3,500 kcal per pound of fat, an 800 kcal per day error equates to ~4 lbs change in body weight over just 4 days.
While analyzing trends may provide some insights, the activity is akin to driving a car using the rearview mirror. We need better tools to monitor nutrition status objectively.
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