Adding the clinical framing, because it changes how the question reads.

Bone density monitoring on lean mass: DEXA bone density at baseline and month 12.

Lumbar spine T-score: -0.9 → -0.7 (stable to slightly improved)
Femoral neck T-score: -0.14 → -0.8 (stable)

No significant bone loss despite 61 lbs of weight loss. Key factors: adequate calcium (1200mg/day), vitamin D (5000 IU/day), resistance training 3x/week, and adequate protein. Weight-bearing exercise is critical for maintaining bone density during rapid weight loss.

claudia_zurich said:

Bone density monitoring on lean mass: DEXA bone density at baseline and month 12.

Same experience, arrived at from the opposite direction. The detail I would add is minor and it is already implied above.

claudia_zurich said:

Bone density monitoring on lean mass: DEXA bone density at baseline and month 12.

Muscle fiber type changes during GLP-1-mediated weight loss, relevant to lean mass: preliminary biopsy data suggests that weight loss shifts the skeletal muscle fiber type distribution:

• Decreased Type IIx (glycolytic, fast-twitch) fibers
• Increased Type I (oxidative, slow-twitch) fibers
• Improved mitochondrial density and function
• Enhanced insulin-stimulated glucose uptake per fiber

This "metabolic remodeling" of muscle may contribute to improved insulin sensitivity independent of total lean mass changes. The muscle you keep becomes metabolically better, even if there's less of it[1].

claudia_zurich said:

Bone density monitoring on lean mass: DEXA bone density at baseline and month 12.

Physical therapist weighing in on lean mass. I work with bariatric and metabolic patients daily.

The resistance training evidence is critical here:

The Lundgren 2024 JAMA paper[1] showed that structured resistance training preserved 73% more lean mass in GLP-1 patients vs medication alone. When discussing lean mass, we MUST include the exercise component.

My minimum prescription: 3x/week compound movements (squat, deadlift, press, row), progressive overload, 7-10K steps/day, and 1.2-1.6g protein/kg/day.

One thing that is still open after claudia_zurich’s answer:

What would you measure differently if you were starting again?