Hi! This happens because your army is constantly growing. The more Units you build, the more Rations you will need to maintain them. You need to upgrade your Drop Zones in order to get more Rations. Also, you can ask other player for tips on this matter 

technically you have to many troops which is putting you in negative, you either need to kill some off or raid daily to gain extra rations so you can keep updating and making more troops...

1. You can check your food consumption in Command Center-Base Stats.
2. You can decrease your consumption by technologies and Control tower. But it won't be easy to get "+" in food production.
3. FYI, Max base decrease is 45% (control tower) + 36% (tech) = 81%. All other bonuses will count from the rest 19%. For ideal example, you have  10 000 cons. 10k*0.19=1900. Hero ability -5% consumtion will count not from 100% (10k*0.05=500, 1900-500=1400 - WRONG), but -5% from rest - 1900*0.95=1805 in total.