Zwang, Congrats on finding a workout you like and doing it!

We have big concerns, too, about undoing the hard work we've done to build muscle mass.

We wouldn't fast at all to lose weight, just to boost the immune system because of the Big C and immune system disorders. The research does show that two to three days of fasting really can reset the immune system, but ... (let me go look up the research notes.)

But prolonged fasting, as in weeks or months, can be really dangerous. At the end of WWII, the military wanted to know the effects of starvation and the best ways to reverse it so they ran controlled experiments. I learned about this in college nutrition classes. The results of the study:

"Among the conclusions from the study was the confirmation that prolonged semi-starvation produces significant increases in depression, hysteria and hypochondriasis as measured using the Minnesota Multiphasic Personality Inventory. Indeed, most of the subjects experienced periods of severe emotional distress and depression.[1]:161 There were extreme reactions to the psychological effects during the experiment including self-mutilation (one subject amputated three fingers of his hand with an axe, though the subject was unsure if he had done so intentionally or accidentally).[5] Participants exhibited a preoccupation with food, both during the starvation period and the rehabilitation phase. Sexual interest was drastically reduced, and the volunteers showed signs of social withdrawal and isolation.[1]:123–124 The participants reported a decline in concentration, comprehension and judgment capabilities ...."

Minnesota Starvation Experiment - Wikipedia, the free encyclopedia

Long-term follow-up showed that some of the participants never recovered all the way emotionally. They became obsessed with food and anything that brought on feelings of deprivation (of any kind) could trigger emotional meltdowns. The calories allowed during the semi-starvation period are actually higher than many popular diets allow today. Makes ya' think!

Zwang, your approach of working out to build muscle sounds smart to me. Keep up the good work and thanks for opening this discussion and putting in the warning for people who have ever had an eating disorder. This is dangerous territory and we're treading it with care. It's been helpful to be able to talk about our experience. Thanks.