About under-reporting in food intake surveys

NHANES is a survey study and under-reporting of food intake is pretty well-known.

Google scholar has thousands reports about underestimation of food intake.

Undereating and underrecording of habitual food intake in obese men: selective underreporting of fat intake

Dietary methods research in the third National Health and Nutrition Examination Survey: underreporting of energy intake

Assessment of Energy Intake Underreporting by Doubly Labeled Water and Observations on Reported Nutrient Intakes in Children

Underreporting of Food Intake by Dietary Recall Is Not Universal: A Comparison of Data from Egyptian and American Women

Actually under-reporting of habitual food intake amongst pregnant American women is so high they should looks like skeletons (according to survey.

You need to know, how read the data. Survey can register changes through time, but it's unreliable as record of events.