There does appear to be a "fat memory" (there's also a muscle memory -- those who've done strength training in their youth will make faster, bigger gains when resuming training later on).
But, absent some underlying organic cause or insult (injury, genetic propensity, illness), the same principles that work for those who have little trouble losing weight work for those who are obese. Perhaps a little more time and effort are involved.
The lesson that's been instructive to me as I travel through the decades has been to watch those who were typically thin as they hit their 30s and 40s. If they aren't practicing good nutrition and activity practices, even they tend towards girth, though it's usually a potbelly rather than an all-encompassing growth.
One you start a heavy diet, you've lost. There may be ways to lose weight that don't prompt the same response for your body. Maybe losing weight much slower? Or alternating fasts with periods of eating well? There is still much research to be done, and many ideas to be tested.
Yep, good point. Considering how much nutritional theory has been turned upside down in the past 10 years it's difficult to know when the body of research will more accurately reflect the numerous subtleties in the ways our bodies work.
Not the most encouraging thing to say to those who are already overweight, but it's an important detail nonetheless.