First, it's "preventive" not "preventative", i.e. preventive care, preventive philosophy, or preventive medicine. I don't know why the first is used rather than the second, but that's the proper usage in medicine. Sorry, it's a pet peeve of mine.
Second, while it depends on the program you are talking about, in general, there is no greater focus on preventive care in osteopathic institutions than in allopathic ones. There is a lot of propaganda suggesting this is a defining quality, but sadly, I have discovered that it is not. The only real difference I've encountered is with the addition of OMM. Other than that, I am hard pressed to find anything different between my education and my colleagues from across the way. As JPH has already mentioned, there is no "osteopathic philosophy." I'm sure this will come as a shock to some. Medical school is essentially medical school, whether you are looking at an allopathic medical school or an osteopathic one (with the exception of OMM, of course).
Third, I do have classes in preventive medicine (but so do allopathic medical schools). So far, however, they have taken a decidedly epidemiological approach, with some biostatistics and EBM weaved into it. I have no comment about this. It is what it is.
Fourth, so far, informally, I have received some instruction in nutrition from across my classes. It's nothing signficant and a far cry from the level to you speak of. However, I am only a first year student, so perhaps, there will be more as I progress. In essence, I agree with you. There should be a bit more formal instruction in nutrition, but there isn't. It's an issue across all medical education. Nevertheless, from another point of view, there is enough to teach already. Schools can barely squeeze in what they want to right now. What will have to give way to squeeze it in? Nutrition is not on the boards as far as I know, so you can probably guess what kind of priority it has. I agree, though, that it is fallen by the wayside and that it isn't unimportant. However, I feel that as physicians we are taught to manage the process of patient care and to be consumate diagnosticians; we can, better than anyone else, develop a differential diagnosis, figure out the etiology of a condition, or pathology, and come up with a treatment plan. I often feel that we learn a little bit of everything, but nothing really in depth. That's the current emphasis in education, for better or worse.
I think it's a good idea to have more training in nutrition, but there is already too much to know. It would be even better to have nutritionists for us to consult and refer patients to. It can also help to have CME for nutrition and maybe even an elective rotation where we get some experience in clinical nutrition.
I don't know. You are right, though, that nutrition has been overlooked and some more instruction wouldn't hurt.