Lighter life has all of the vitamins needed daily and is a low carb type of protein shake where as slim fast is very high in carb and sugar I think. Also with lighterlife your body goes into a ketogenic state and I doubt slim fast does. I hope that's a bit of a help! Also with lighterlife there is weekly cbt therapy which really does help. I'm sure some of the other very helpful ladies on here will give some more information or correct anything that I've said which isn't correct! Xx