It seems as if a time during which food intake is limited would be a severe weakness for soldiers. Are there any examples of this influencing warfare?
I don't think so, because Muslims can be exempt from fasting for several reasons, and fighting a war is one of those.
Narrated Ubaidullah bin Abdullah bin Utba: Ibn Abbas said, Allah's Apostle fought the Ghazwa (i.e. battles of Al-Fath during Ramadan."Narrated Az-Zuhri: Ibn Al-Musaiyab (also) said the same. Ibn `Abbas added, "The Prophet fasted and when he reached Al-Kadid, a place where there is water between Kudaid and 'Usfan, he broke his fast and did not fast afterwards till the whole month had passed away.