"It compared outcomes in a group assigned a target of 25% CR (i.e., a 25% reduction in energy intake below baseline levels) with outcomes in an ad libitum diet control group. "
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"
It just means eating 12% fewer calories than your baseline to maintain your current weight. So if you eat 2,500 calories per day to keep your weight and activity levels, bump it down to 2,200 and keep it there. I have heard that it is possible to build muscle while "cutting" (calorie restricting) but it's going to be much slower and probably more uncomfortable. Note that this study was a 12% restriction maintained for 2 years. The metabolic and inflammatory benefits persist long after the calorie restriction period in animal models, and this study seems to show the same genetic pathways are getting upregulated and downregulated in humans as we have seen in the animals that benefit from longer lifespan after calorie restricting.
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.
and
"... CALERIE TM participant requirements included:
Source - https://calerie.duke.edu/background