Just know that there's a difference between "multigrain" and "wholegrain".
Whether it's wholewheat or wholegrain, it's the "whole" part that's important...nutritionally.
Multigrain just means there is more than one type of grain. It doesn't mean it's wholegrain.
There is nothing wrong with eating grains as long as they are whole grains. There is nothing wrong with eating carbs -- all vegetables are carbs. It's the simple carbs that are the problem. And eating grains doesn't mean you have to eat flour -- you can just eat the grain, just as you do with brown rice or oatmeal. The real problem grain is wheat, because it's human-invented -- there is no wild wheat. It was hybridized by humans from other grains, just as cows were hybridized by humans and there are no wild cows in nature. Some grains, or seeds that are eaten as grains, contain nearly as much protein as beans, such as quinoa and amaranth and millet. As to the argument against multi-grain foods, some believe that eating too many different foods at one meal present a problem for the digestive system. This can get extremely involved and is called food combining, and the belief is that the digestive system can't do several things at once. I have no idea if this is true or not. The biggest no-no in this theory is eating fruit with anything else, but also argues against combining protein foods with other foods. My own feeling is our systems have adapted to this but at some point you overdo it, so eating some of these products, such as 15 grain mixes that exist, are probably too much to handle as the digestive system might get overtaxed.
Compared to whites, it is healthy! But they still are flour-based, (breads, pastas,crackers etc) thus carb-filled. The best way to eat them, as i found out for myself, is to reduce them.
http://www.drperlmutter.com/about/grain-brain-by-david-perlmutter/
http://beyetransformed.org/wp-content/uploads/2011/01/BYTBSS-Soul-Is-Todays-Wheat-Making-you-Gain-Weight.pdf
Multi grain food is valuable and studies about a nutrition enriched with multi grain food have only good things to say.
Take care