Grains actually lose most of their vitamins and minerals when they are processed (the nutrients are in the germ of the grain with is discarded) so I would suggests they are poor source of B vitamins and minerals such as magnesium.
So don't eat processed grains, eat them whole instead.
Low carb works for some, and not for others. I don't want to argue the health merits of either (that's been done a thousand times before here and elsewhere) but for those who can't/don't want to/don't believe in low carbing, can we agree that eating the grain as close to its natural state is the best option?
Take a food like pearled barley: it has a glycemic load of 11-25 (depending what source you use) which puts it lower than most fruit, many vegetables and a lot of dairy products. (On some charts, it's lower than green beans, which it seems my low carbing friends eat by the truckload. ) Pearl barley is high in fiber, B vitamins, several minerals, and iron. How is this a bad food?
For a lot of people, it is more realistic to make better choices about the carbs they do eat than to eliminate them altogether. Certainly, a low carb lifestyle works really well for some people, but I think it's important to make a distinction between whole and refined grains when discussing dietary choices.