The intervention group followed a 3-phase diet:

A 15-day very-low-calorie diet (600 to 800 kilocalories per day)
A 2-week, 1,200-calorie diet with meal replacement for dinner and biweekly consultations
A maintenance phase with a 1,200-calorie to 1,800-calorie Mediterranean diet and 150 minutes per week of unsupervised exercise

Compared to the control group (given general diet and exercise advice), the intervention group showed the following:

Reductions in visceral fat
Improvements in C-reactive protein, HDL cholesterol, and HbA1c levels
A shift from severe to mild or moderate apnea (28% of participants), which allowed discontinuation of continuous positive airway pressure (CPAP) treatment

At the trial's end, 44.4% of the intervention group maintained their calorie deficit target and 17.6% met weekly physical activity targets.

For obstructive sleep apnea, lifestyle changes improve sleep quality Original paper