Modern diets are crap and people are eating a lot more than they realize with such calorie dense foods.  If you want to say that hormones play a role, that's fine, but differences in hormones or metabolism only changes the amount a person needs by just a few hundred calories a day at the very most (200-300 max). Changing what you eat doesn't cause your hormones to magically change and somehow alter the measurement of a calorie.  You were the same weight on the two different diets because you were eating the same number of calories, but you were miscounting somewhere.  People eat a lot more carbs than they realize because the body can process them faster than protein and they're extremely dense in calories.  It's a bad combination for people that can't keep extremely close track of what they eat. Also, there are quite a few medical professionals here, including myself.  We've actually studied this for years as opposed to a 5 minute google search.