Abstract: The weighing instrument has a receiving tray and an index mark displaceable in front of a fixed dial graduated in weight. It comprises means enabling the user to place, in a position enabling it to operate in association with said index mark, any one of several removable scales which are calibrated, for categories of foods of similar characteristics, in at least one of the magnitudes involved in dietetics and proportional to the weight of the foodstuffs placed on the tray. The instrument is useful in feeding in cases of obesity, diabetes, low calorie, low sugar, low protein, low fat or low residue, etc. diets.