I don't remember optional classes in grad school, lol!
Absolutely, you have to stay up on research and what's new coming down the pipeline. Don't want a patient asking about something and you having no idea. I see it hard to blame them for not knowing it all. Just think of all the crap MD/DO's need to know when seeing patients on a daily. That's why they refer out. My MD at the VA back home gave me a referal to see the nutritionist. I humored her and went. The nutriotinst looked at me and said, "you're obese?" Then we spent my hour talking about the use of insulin in bodybuilding. She was blown away to know there are other uses to insulin.
When I did my graduate work I fortunately had a few options too. I also did a double area of interest so I was able to some what pick and choose between exercise science and sport nutrition graduate level classes. I guess MD's have a lot of options depending on what they want to specialize in.
You know in some states it is against the law to practice nutrition without being a RD. Seems like you are right, the best thing doctors could do professionally is refer a patient to a registered dietitian instead of trying to practice in a field they are not competent in.
As you pointed out, my faith in registered dietitians is not so good either. I had a lot of trouble in nutrition because I though outside of the box. My professor was horrified that I was using creatine back in the early 90's. She was just as horrified that I was using protein supplements....after all it is not really food and definitely going to cause me kidney problems.
I also had a exercise physiology professor I always talked to. His office was loaded with books but they all were old, dusty and had spider webs on them. They guy had not updated his knowledge since he got his PhD. He thought I was crazy to actually think that you could be health lifting weights. After all aerobics was they only way.