The basic daily food rations shall be sufficient in quantity, quality and variety to keep prisoners of war in good health and to prevent loss of weight or the development of nutritional deficiencies. Account shall also be taken of the habitual diet of the prisoners.
The Detaining Power shall supply prisoners of war who work with such additional rations as are necessary for the labour on which they are employed.
Sufficient drinking water shall be supplied to prisoners of war. The use of tobacco shall be permitted.
Prisoners of war shall, as far as possible, be associated with the preparation of their meals; they may be employed for that purpose in the kitchens. Furthermore, they shall be given the means of preparing, themselves, the additional food in their possession.
Adequate premises shall be provided for messing.
Collective disciplinary measures affecting food are prohibited.
That’s a Geneva Convention violation.
Geneva Convention Relative to the Treatment of Prisoners of War:
https://www.ohchr.org/en/instruments-mechanisms/instruments/geneva-convention-relative-treatment-prisoners-war