Biological processes of fat loss and muscle preservation

When the body metabolizes fat, the primary organ responsible for its removal is the lungs. According to research published in The BMJ by Ruben Meerman and Andrew Brown, approximately 84 percent of metabolized fat mass is expelled from the body as carbon dioxide through exhalation. The remaining 16 percent is converted into water, which is eliminated through urine, sweat, and other bodily fluids.

While weight loss is a common health goal, experts emphasize that losing kilograms does not necessarily mean losing fat. Without strength training, individuals may lose muscle mass or other lean tissues alongside fat. Maintaining muscle is critical for functional strength, metabolic health, and the ability to perform daily tasks such as climbing stairs or lifting objects.