Microwaves heat food and drinks by generating friction, causing molecules to be torn apart and deformed. The structure of the molecules is then changed into a form unrecognised by the body.
As far back as 1989, an article in the Lancet advised mothers to avoid heating up baby milk in the microwave. (Baby milk is crucial for a baby’s immune system development and by shoving it in a microwave: its disease-fighting capabilities are destroyed.
If you microwave food, the structure of it is changed and not recognised by the body. Nutrients are destroyed. If you have access to a stove at lunchtime, use it. If you don’t, invest in a food thermos. I use this one: your food will still be hot if you prepare it the night before, and if you want it for supper, it will still be warm if you heat it before you head off in the morning.
Avoid the work microwave: it will make your breakfast, lunch and/or dinner a nutritionally void hot mess.