Hey college-student, from what I know, therapeutic and medical treatments are the only treatments for BPD with any evidence to back them up. While eating healthily is good for your body in general, it is unlikely to be an effective treatment for BPD.
Also, a quick review of the BPD literature (via PsycINFO and MEDLINE -- two of the most commonly used databases for psychological and medical research) indicates that while there is some research to show that eating healthy foods and maintaining a healthy weight are likely to improve overall mood, psychiatric drugs alongside appropriate psychological therapies (and eating healthily always helps) is the best approach.
Of the most recent 60 articles....
-23 concerned treatment of BPD with various drugs (and appeared to be in agreement based on glances at the abstracts)
-3 were specifically on psychotherapy and using it as an adjunct to drug therapy
-2 claimed eating well is a good way to improve mood, which *may* be helpful with BPD
-1 claimed BPD could be helped by eating foods high in Omega-3's*
-1 study examined the Omega-3 claim and overturned it as a placebo effect due to its inconsistency in effectiveness across studies (meaning the effect of omega-3 fatty acids may be nothing more than a placebo effect due to expectation of improvement and/or demand effects and so forth in the experiment)