In response, Erik Arnesen shared another year long 5:2 intermittent fasting vs. continuous energy restriction study where the drop out rate at the end of year one was just 7% and the average loss was 20lbs! (and actually I blogged about this one in the past - tl;dr no difference in outcomes but 5:2 participants were hungrier)
If the diets were identical, why the tremendous difference in adherence and weight loss at a year?
Sure, could be different patient populations, but I'm guessing the much larger factor was the service provision. Because at the end of the day that's a huge part of what's being measured in any organized diet study. Not just in terms of how many visits or touch-points a particular program has, or what collateral materials and support they provide their participants, but also the rapport development, motivational ability, and teaching skills of the service providers themselves.
Having led an inter-professional team for 16 years, I can tell you that who you've got helping your patients/participants has a tremendous impact on their outcomes even within the same program's delivery.
So the next time you consider the outcomes of any study's diet arm, a question worth pondering is how much of those outcomes are consequent to the prescribed diet itself, and how much are consequent to the health care professionals administering it?