So, I remember many changes - and I am not yet in my 50's - here are a few examples:

1. Margarine
Was: Way better than butter
Now: Actually worse, unless no trans-fat.

2. Four Food Groups
Was: THE standard
Now: Replaced by "A Pattern for Daily Food Choices"

3. Meat:
Was: Essential and large part of a healthy meal
Now: High in fat, better if portions are small

4. etc..

My favorite article and writer on this subject:

http://www.nytimes.com/2007/01/28/magazine/28nutritionism.t.html?n=Top/R...

Eric