The overwhelming consensus online is that microwaving a babies bottle can be "dangerous" because microwaving formula can produce hot spots. However, if you simply swirl the bottle you can even out the heat distribution and eliminate said hot spots. The amount of bubbles produced by swirling is minimal and heat redistributes very easily in liquid. That being the case, if I test the formula's heat and its a good temperature, and the heat is redistributed, whats the big deal about microwaving the bottle? Is it just that people can't be trusted to swirl the bottle well and test the temperature?
Unfortunately, I don't have access to the full articles, but for what its worth, here are a few articles which discuss the nutritional effects of microwaving formula and/or breastmilk (thanks to @bestander);
- http://www.ncbi.nlm.nih.gov/pubmed/8889628 - Says there are no effects on B1/E/acids if the resulting average heat is not higher than 60 C
- http://www.ncbi.nlm.nih.gov/pubmed/11403146 - Reinforcement of first study results, showing no difference in B1/B6 levels if compared to stove top heating
- http://m.pediatrics.aappublications.org/content/89/4/667.short - E.coli bacteria grows faster in microwaved milk than control, i.e. antibacterial qualities are reduced
- http://pediatrics.aappublications.org/content/90/3/412.abstract - There is no significant loss of either riboflavin or vitamin C. Routine mixing resulted in formula temperatures which could safely be fed to infants. "portions reached a mean temperature of 44.7 C"
- http://www.ncbi.nlm.nih.gov/pubmed/2189981 - abstract is missing results