MRP Diets

Are MRP Diets really bad for you? The few times I truly “leaned out” (under 5-6% BF) were on MRP diets. And I mean fairly severe ones. I would eat 6 meals a day (5 MRP’s + flax, DHA/EPA, or CLA + Fiber Tabs, and 1 “real food” meal a day). I would do this for 3-5 month stretches (clearly flavor doesn’t play a major role in my life). I’ve been told many times this is an unhealthy diet and I’ve even read so on this site. I want to know why. I have a hard time dropping BF and keeping my LBM without utilizing this diet. Anybody else believe in this diet? Any feedback would be appreciated, thanks.