Adipose tissue retains an epigenetic memory of obesity after weight loss

As someone who's struggled with weight loss, and have known others to struggle with it well, I think we colloquially called this "slow metabolism".

It always did feel like it was easier to gain weight than lose it, especially fat weight and not muscle weight for me.

I was recently sent a video about fat adaptation (basically teaching your body to be better at burning fat) by a very fit friend, but I wonder how much of that is bro science and how much of it is grounded in reality. Maybe worth looking into more deeply if it can counteract or balance out this.

metabolism is orthogonal . It's possible to have a fast metabolism and still be obese if you're eating at a surplus. But it's also possible people with faster metabolisms may be more successful at weight loss if already obese. So a 300-lbs person who eats 10,000 calories/day to be weight stable will find it easier to lose weight compared to to a 300 lbs person who is stable at 4,000 cal/day. This can also explain how some people lose tons of weight on GLP-1 drugs, whereas others lose less. The guy eating 10,000 calories/day will lose much more weight more rapidly owning to having a much bigger metabolic furnace, as soon as he restricts eating and his body is no longer getting 10,000 calories/day. Unfortunately, there are no studies that investigate the link, if any, with metabolism and dieting success.

10k calories a day is what a black bear eats preparing for hibernation. And it is what Michael Phelps would eat daily when training in the pool for hours on end.

Obese people can remain obese eating 1000 calories a day. I recall one episode of My 600lb Life and the show's featured person that day was at 900 or 1200 calories a day and still didn't lose weight. Might have still been gaining.

It is a dynamic system. People tend to only consider the CI in CI/CO.