Both the pyramid and its replacement, the plate, are supposed to provide a visual representation to guide healthy eating.
Given the high levels of obesity in the U.S., the pyramid wasn’t doing its job. According to the New York Times article, Goodbye Food Pyramid, Hello Dinner Plate, (http://www.nytimes.com/2011/05/28/health/nutrition/28plate.html?hp), the pyramid “basically conveys no useful information.”
Originally intended to communicate the building blocks of healthy eating by showing food groups in horizontal bands in roughly some relation to the proportions in which people should eat them, the pyramid was reworked before its first introduction to address concerns by the dairy and meat industries that it under-represented those types of foods (as was the intention).
Later, the proportional horizontal bars were replaced by vertical ones that present all food groups on an equal footing (which diet experts say, they’re not).
The replacement image, a plate, is like a pie chart (the pie reference is not intended as a dietary suggestion) that roughly shows foods in the proportions that people should eat them.
Check it out for yourself.
As a professional communicator, I empathize with the challenge facing the people who designed the plate: how to clearly convey useful technical information while acknowledging some difficult political choices.