I've written in the past about the importance of having dinner as a family--even if it's 4-5 times a week. It's well documented that kids who eat the majority of their meals as a family do better in school They also have a lower chance of having trouble with drugs, smoking and run-ins with the law.
In addition, it's been found that kids who enjoy dinners with their families tend to have better relationships with their parents and parents know more about what goes on in their kids' lives--simply from the dinner table conversation.
You can read an old post of mine with some interesting info regarding these statistics here.
article about a study that gives yet another reason to have family dinners. According to the study, kids who sit at the dinner table for 20 minutes or more were more likely to have a healthy weight than those who didn't. A difference of only a couple minutes per meal could make a difference. While the article doesn't go into great detail as to why this is the case, it shows that the simple communication between family members makes a difference as well as having a scheduled meal time.
Personally, it seems to me that eating like this helps the child to eat slower (as opposed to shoving fast food down their throats in the car), which helps maintain a healthy weight. And I would think that if a family takes the time to sit down for a dinner together, the meal will tend to be balanced and somewhat nutritional.
I don't know. But what I do know is that there are loads of great reasons to take the time and eat dinners as a family. It's something, sadly, that seems to be less and less prevalent in our society, but is such a simple way to make a difference in the life of our kids.