Hi

That’s a challenging questions, since my opinion is based on about 15 years of observations and learning I’ve stumbled across on the subject.

One book I might recommend is Cognitive Neuroscience by Banich and Compton. It discusses brain development and discusses how so much of what and who we think we are is deeply rooted in neurobiology.

https://www.amazon.com/Marie-T-Banich/e/B003VOS9T6/ref=aufs_dp_mata_dsk

I might also suggest looking into Dr. Asher Larmie, who has made a specialty of the study of weight loss as it relates to biology.

https://www.fatdoctor.co.uk/

Also, Neuroscientist Sandra Aamodt

https://www.ted.com/talks/sandra_aamodt_why_dieting_doesn_t_usually_work?subtitle=de

And Dr. Herman Pontzer’s research of how calories are actually used and stored in the body.

https://www.science.org/content/article/scientist-busts-myths-about-how-humans-burn-calories-and-why

Of course, no single professional’s opinion makes a “scientific fact” – so I would recommend looking generally into the subjects of biological weight set-points controllers such as the hypothalamus (there’s an interesting primer at https://www.obesityaction.org/resources/body-weight-set-point-what-we-know-and-what-we-dont-know/), weight controlling hormones like leptin, and general data and statistics on how the body will alter during weight loss in an attempt to retain calories during dieting and exercise even if it needs to pull calories from other sources than fat or digestion.

These are, of course, just starting points. I wish you the best of luck in your discovery journey.