Personally, I think a lot depends on a person's age and what meds they are taking. WHen I was in my early 30s I went on Atkins for the first time and I lost 13 lb in the first week and steadily after that. I had no trouble getting into deep ketosis and I felt marvelous and full of energy. Now that I'm much older and on several prescription meds, it's much more difficult for me to lose weight on ANY weight loss plan. Getting old is a b***h but it sure beats the alternative.