Weight lost is not all fat. Some proportion comes from lean tissue — muscle included — unless steps are taken to limit it. The faster the loss and the lower the protein intake, the larger that proportion tends to be.
Why it matters
Muscle is where glucose goes. Skeletal muscle is the largest site of glucose disposal in the body. Less muscle means less capacity to clear glucose from the blood, which works directly against what metabolic treatment is trying to achieve.
Muscle affects energy expenditure. Losing it lowers resting energy requirements, making maintenance harder afterwards.
Muscle is function. Strength, balance, stability and independence — increasingly consequential with age, and the reason this matters more for older adults than younger ones.
The pattern that causes trouble: weight lost with a significant muscle component, followed by regain that is predominantly fat. Repeated over cycles, body composition worsens even if weight returns to the same number.
What limits muscle loss
Resistance training. The most effective single intervention. Signalling muscle that it's needed is what prompts the body to preserve it. Two or more sessions a week covering major muscle groups is the usual recommendation — bodyweight, bands or weights all work.
Adequate protein. Requirements are higher during weight loss than at weight maintenance, and spreading intake across meals is more effective than concentrating it. Specific amounts should come from a dietitian who knows your weight, kidney function and circumstances.
Avoiding excessively rapid loss. Faster isn't better here. Very rapid loss increases the lean tissue proportion.
Adequate overall intake. Very low intake accelerates muscle loss regardless of protein composition.
During medical treatment specifically
When appetite is markedly reduced, protein intake often falls without anyone noticing — food volume drops and protein-dense foods are frequently the ones people find least appealing. This is one of the more common reasons for dietitian referral during treatment, and it's worth pre-empting rather than correcting.
Related: Nutrition during weight management · Eating patterns, activity and sleep Next: Find an exercise physiologist or dietitian →
Educational information only. Not a substitute for medical advice — speak to a qualified health practitioner about your circumstances.