If someone has been training “intensely” for a lengthy period of time (this means months/years, not weeks) they have primed their metabolism and kept it more flexible because being “consistent” with nutrition and exercise will make the metabolism function at a greater capacity because the body demands more nutrients to support new muscle tissue, increased activity, etc..
The less active and adherent to healthy nutrition principles a person is, their metabolic function is likely less flexible. As very general rule, the healthier the habits, the more flexible an individual’s metabolism will be.
So what does this tell you about achieving lasting results? That consistency over time (not perfection for 12 weeks) leads to better body composition, better health, less systemic stress/inflammation, more optimal gut health, etc… Pretty much every thing that leads to better performance and health.