Both subjects are off topic and neither tag should exist at all.
If you think that the question can be rephrased as pertaining more to either food preparation or food safety (the latter falling under the on-topic food handling category), please edit and retag the question. Otherwise, you should vote to close. If I look at the 21
[health] questions, I see many questions that, IMO, really don't belong here.
(Note: There is one exceptional case that the community appears to agree on, and that is allergies. This exception makes sense to me because cooking for somebody with allergies requires many special precautions and techniques. Those questions should be tagged specifically as
[health] is superfluous.)
P.S. In case you're wondering, I don't think your question is off-topic because microwaving is still cooking. I don't think it really needs either the
[nutrition] tags, though.
Update: I wanted to mention that my problem with these tags isn't just that they're off-topic. It's also that their meaning is completely subjective. Every cook wants to make healthy and nutritious meals, but what does that actually mean? Low-fat? Low-sugar? Low-carb? Gluten-free? Non-allergenic? Low-acid? High-fiber? High-protein? All of these things are "healthy" to someone, depending on their genes and their lifestyle. And all of those subjects would make great tags. But
[health] is practically useless because even somebody who is interested in health issues is going to have a hard time finding what they're looking for in that tag. And
[nutrition] really isn't far off.
If a question is so general that it can't be pinned down to a specific health or nutrition concern, then it can't really be answered in any meaningful way (not in the context of a cooking site, anyway). I rank these tags even lower than
[technique] in terms of their actual utility.