The Scale Is Going Down. But What Are You Actually Losing?

Body weight reflects not only fat tissue, but also muscle mass, organs, bones, water, and digestive contents. This is why rapid day-to-day changes are rarely caused by actual changes in body fat.

At the beginning of a diet, some of the weight loss may come from a reduction in glycogen stores and the water associated with them. Salt and carbohydrate intake, hydration, the menstrual cycle, and bowel movements can temporarily affect the number on the scale without a significant change in fat mass.

Over the long term, an energy deficit reduces fat tissue, but it may also lead to a loss of lean mass, which includes muscle, water, organs, bones, and other non-fat tissues. This can occur both with lifestyle interventions and during treatment with incretin agonists, although resistance training can help preserve muscle mass more effectively.

Muscle contributes to mobility, balance, strength, and glucose use. Excessive muscle loss can reduce functional capacity and make it more difficult to maintain an active lifestyle. For this reason, the success of weight loss should not be assessed solely by the number of kilograms lost.

Strength training is essential for protecting muscle. Exercises using weights, machines, resistance bands, or body weight help maintain muscle tissue. When combined with a dietary intervention, they may promote fat loss, preserve lean mass, and increase strength, even if total weight loss does not differ significantly from diet alone. The World Health Organization recommends exercises targeting the major muscle groups on at least two days per week.

Adequate protein intake and a sustainable energy deficit are equally important. Protein requirements should be tailored according to age, weight, activity level, and associated medical conditions, but protein intake cannot replace the stimulus provided by exercise. Highly restrictive diets, insufficient food intake, and a lack of physical activity may promote lean mass loss, including during obesity treatment; in chronic kidney disease, protein intake should be determined together with a doctor.

Weight remains a useful indicator, but it should be interpreted as a trend rather than a daily verdict. Waist circumference, how clothes fit, changes in strength, and the ability to carry out usual activities provide a more complete picture. If weight decreases but the person becomes more tired and progressively loses strength, the plan should be reassessed.

Bioelectrical impedance analysis, including InBody, estimates fat mass, lean mass, muscle mass, and body water distribution. It is a quick and non-invasive method, but it does not directly measure tissues, and the results may be influenced by hydration, recent meals, physical exercise, and fluid distribution. For this reason, tracking changes over time is more useful than interpreting a single measurement in isolation.

For comparable results, measurements should be repeated on the same device and under similar conditions: at approximately the same time of day, with a similar hydration level, and without intense exercise before the assessment. At the clinic, InBody analysis can be interpreted together with medical history, waist circumference, laboratory test results, diet, and physical activity, providing an additional reference point for personalising the plan and monitoring progress.