Doctors could have been sued for telling patients to eat more than 35% fat (if the patient had any bad outcome) and the old guidelines could have stood against them in court. My wife's cardiology group regularly discussed that hospital policy prohibited going against ACC guideliness (without a lot of waivers or documented justifications) and the ACC and USDA had an upper limit of 35% fat (which was actually raised 5 years ago from 30%). At one point the USDA had a 55% to 70% carb range in their guidelines. in 2010 it went down to about 45-65% depending on how you interpret the protein guidelines. Now it would stand at anywhere from 25% to 65% as they still recommend about 25% carbs to meat basic brain needs. Next up may be removal of any saturated fat limit.