Where these data are coming from?

For proteins, fat, carbs, fibers and calories the sources are:
  1. the USDA database, release 24, compiling more than 8000 foods [1],
  2. the CIQUAL table, published by the french "Observatoire de la composition nutritionnelle des aliments" (see [2]).

References

[1] « Composition of Foods, Raw, Processed, Prepared » USDA National Nutrient Database for Standard Reference, Release 24 (2011)
[2] « Composition nutritionnelle des aliments » TABLE Ciqual, ANSES (2012)
[3] « Ingrédients des cérérales pour le petit déjeuner Kellogg’s », www.kelloggs.fr (2012)
[4] « Valeurs nutritionnelles des en-cas céréaliers Kellogg's », www.kelloggs.fr (2012)
[5] « Les_produits_LU_pour_le_gouter.pdf », www.lu-france.fr, (2012)
[6] Chiu C.J. et al, « Informing food choices and health outcomes by use of the dietary glycemic index», Nutr Rev. 69(4): 231–242 (2011).
[7] Wolever T. M. S. et al, «Food glycemic index, as given in Glycemic Index tables, is a significant determinant of glycemic responses elicited by composite breakfast meals», Am J Clin Nutr 83:1306–1312 (2006).
[8]    Atkinson FS, et al. "International Tables of Glycemic Index and Glycemic Load Values": Diab Care 31(12), (2008).
[9]    www.glycemicindex.com
[10]  www.observatoiredupain.fr