The upper part of the figure shows the before and after cross-sectional image of a subject with obesity who has followed a diet-only intervention to lose body fat.
In the lower part of the figure, the before and after image of another person with obesity who has followed an intervention to lose fat, but this time combining diet and training.
In the case above (example 1), we see the effects on body weight, fat mass and muscle mass after the diet-only intervention. Although there was a large loss of body fat, there was also too high a loss of muscle mass. This loss of lean tissue will imply not only a possible worsening of health, but also a possible regain of lost body fat in the medium to long term.
However, in the case below (example 2), where diet and exercise (strength + cardio) were combined, although less total weight and body fat percentage was lost, muscle mass not only did not decrease, but also increased.
Muscle strength also increased, implying an improvement in muscle quality. Undoubtedly, this second intervention is a better option than the first one of diet alone.
Therefore, we see how in the case above, although the subject lost more total weight, the result was worse than in the case below. And the fact is that simply relying on body weight is a mistake.
Too many people worry too much about the data reported by the scale, i.e. the weight, when in fact this data alone is of little use, except in extreme cases of underweight or overweight. If the scales show a drop in weight, but this loss implies a severe reduction in muscle mass, the result will be disastrous.
Stop worrying so much about whether the scale goes up or down, because this data alone does not indicate that you are getting better or worse, it may even be the opposite of what you think. Basing yourself on this will only generate frustration and an unrealistic perception of the process.