How to warm up canned beans

This isn't the "quick" nor the healthy answer, but I personally do a twice-cooked system. I leave the juice from the can in the mix, and boil it down, which takes 15 minutes or so. Retaining the flavor of the canned fluid is essential, in my opinion.

Then I "fry" the dry-ish mixture which is beginning to separate in maybe 1 tbsp preheated lard per can of beans, stirring a lot at first. Lastly, very slightly simmer this on low heat for 1 hour or so, stirring occasionally. Flavor is awesome. Any kinds of beans can be prepared in this way, and it is similar (varying on oil and legume variety) to other paste concoctions created elsewhere.. such as in the middle east.

Note that this method negates the need for lots of "mashing". So, if you're more looking for less effort, than necessarily for "quick".. this could be your answer :)

I finally found what I'm looking for, from the University of Michigan - some actual data on the subject!

They say that rinsing canned beans can reduce the amount of sodium by half, and also reduces the amount of complex sugars which humans can't digest (but the bacteria in our intestines can, with uncomfortable results!)

It appears that draining the fluid is likely to improve the flavor and texture of the resulting food by concentrating the flavor of the beans -- unless you're following a soup recipe that specifically suggests retaining the liquid to thicken the soup.

I still haven't found any information about what healthy nutrients might be lost by rinsing the beans, but the general consensus seems to be that it rinsing will do more good than harm in almost all cases.