Once my backpakcing was upgraded it seemd as tho I was still only able to hold the original amount of weight.
although today I further found out that it does work. trying to hold health and food (Maby armor as well) wont be accepted after you go over the "stock" maximum weight of your backpack.
this can be worked around by dropping tools, like turrets and miners and such, picking up the desired food or health. and then picking up your tools again
Lost/Eldar please contact me if this made no sence. PEACE!