12% reduction of what? The basal metabolism? Were the people overeating before? How many calories on average?
and
"... CALERIE TM participant requirements included:
Absence of significant health problems, including diabetes, cancer, heart and liver disease, and AIDS
Absence of medication use except oral contraceptives
Age from 20 to 50 (inclusive) for men and ages 20-47 (inclusive) for women
Body mass index (BMI) of 22-27.9 (lean to slightly overweight)
No recent substantial weight loss
No history of eating disorders, behavioral, or psychiatric problems
Use by women of an acceptable form of contraception throughout the study"
I want to live longer. I would also like to build some more muscle, ideally to a BMI of 22. What if I gain 10lbs of muscle then restrict?
When you put on 10 lbs of muscle, presumably your baseline will be slightly higher than it was prior to that (extra muscle requires extra calories to maintain), but still less than what it took to put that muscle on quickly and efficiently. I have no clue how much you should expect that difference to be, I'm sure many a bro scientist has opinions on it, some of which may be reasonable. Bulking and cutting is a classic technique in bodybuilding, however, typical cuts go on for a few months at most as opposed to 2 years.
One major takeaway from this study is that on average, you will be just as strong as when you started calorie restricting even though you will have lost muscle mass. It is theorized that your muscles will have become more efficient, so if you put on more muscle after a long period of calorie restriction you will be considerably stronger than if you had skipped the calorie restriction and just added the muscle. Food for thought.