Jennifer Aniston follows the 80/20 rule when it comes to her diet.Myung J. Chun/Los Angeles Times via Getty ImagesJennifer Aniston, 55, exercises regularly and keeps her diet in check with the 80/20 rule.The 80/20 rule involves eating healthily 80% of the time and being more lenient during the other 20%."I give myself days where I can have whatever I want.