A meta-analysis of 29 long term weight loss studies[1] found:
> By 5 years, more than 80% of lost weight was regained
I think a much better hypothesis is that CICO does work, physically, but there are metabolic, hormonal and mental factors that either predispose towards obesity or make it difficult to escape.
It's a bit like telling gambling addicts to "just stop gambling" or depressed people to "lighten up".
And along comes GLP-1 drugs, where obese people find it easy to lose weight, find new motivation for life, etc. The GLP-1s aren't increasing metabolism, nor are they making people exercise, nor are they making food less available. Yet somehow, a hormonal mediation is greatly successful, hmm.