Mathilde, I believe that you do not have the things very clear.
There is a thing that is called a constitutional thinness, which in case of Letizia is evident, only it is necessary to see images of her sisters, or of her aunt Henar. The persons who have it, have a natural trend to slim because they have fewer cells of fat. They are healthy persons, who feed well, but that have many difficulties to gain weight. To gain weight there need special, rich diets in proteins and the reduction of the physical activity, and nonetheless they gain weight very little by little.
A normal person who has a life with very much stress and many activity, is in the habit of losing weight ... for a normal person this loss of weight can make them marvellous. But for a person who is thin, this loss of weight makes them too thin, and to recover these kilos is very difficult for them.
You put examples of normal persons, or even of the persons with trend to put on weight .... in no case, these persons have not the same Letizia's metabolism.
I am going to put the example of the Spanish Royal Family. Do you know that the Spanish Royal Family is always to diet? The Borbones have a trend to put on weight, and have to look after very much not to put on weight. The aspect of the Infantas is derived from a strict physical care, they are below their weight, only it is necessary to see her images in the 80 ... and it seems to nobody to be rare, for many people they are marvellous ... but really they are below their weight.
This permanent diet of Zarzuela, has provoked curious anecdotes. The Infanta Cristina commented on a journalist that shehad to look after very much because but instead of "Infanta" she would be call it an " elefanta" (elephant). When Letizia was promised of the Prince and she installed in Zarzuela, the press was commenting that often was going to eat to mother's house (' food domestic and more consistent than that of Zarzuela).
And the best example. The Prince has slimmed enough, he had gained a few kilos and now he has lost them, something of diet and the intense activity they will have contributed. If the prince does not look after himself he can end tremendously. If in the Prince, who is a burly man, with facility to put on weight, the intense activity to contributed in order that he slims .... in his wife who is thin, and she loses weight with facility the loss of kilos is evident. Probably he has lost more kilos, but 5 kilos that make the Prince marvellous, they make Letizia very thin.
The Letizia's only options to put on weight would be a very studied diet and to reduce the activity and the stress ... first difficult but possible (they eat often out of house) ... the second totally impossible one. Since Donna has said, the agenda of the Princes in the last months has been exhausting, when one has such an intense activity the normal thing is that weight gets lost a little. If to it you join a life with many pressure and stress ... you have a time bomb ... that has made the prince marvellous, but that has made Letizia very thin (and it will be difficult to her to recover very much these kilos, because her metabolism gains grams very little by little, and because her life is going to continue being equal).
Finally it is good to rememberall the barbarities that were said and wrote in January, 2005 ... and as the May Leonor's arrival was annunced. The reality finishes always being imposed.