I'm a meat eater. But mostly fish like salmon and good dairy, such as unprocessed greek yogurt (I have no dairy issues). In my 30s for about 8 years I was mainly ovo-lacto vegetarian. Now in my 60s.
Now I try to eat an anti-inflammatory diet, especially with few refined starches. I have low blood pressure (good), low to moderate blood sugar (good) and no other problems except an extremely hyper-reactive immune system (asthma and an intolerance to any foreign substances in my body like any type of stitches).
Confused as to why people here continue to think their immune system is "weak" and that is why they have LP or OLP and other autoimmune diseases, when the exact opposite is true.
Sorry, but this is mostly genetic people, with maybe a drug or environmental trigger. Your immune system served you very well in pre-modern times. Now it doesn't have anything to keep it under control, such as lots of nasty pathogens and parasites, so it starts attacking you. I don't live in the UK (in US), but have UK heritage. I have noticed from the literature that many OLP patients from the UK have HLA B57, the elite controller gene (as I do). This gene makes you almost immune (or a long-term nonprogressor) to the HIV virus and the hepatitis C virus. Our ancestors may have been immune to the smallpox virus and/or bubonic plague. The downside is that you have super aggressive T-Cells that may attack you as well.
Plus I have the HLA "super B-8" allelles (the Scandanavian/British Isles HLA genotype) that has a strong association with autoimmune diseases. Maybe these genes were great for our viking and celtic ancestors, but problematic in modern times.
Liver, celiac and thryoid disease have been associated with LP and OLP. So that is important. If you have celiac disease (also associated with northern European heritage), then you should, follow a gluten free diet. Liver diseases, including hemochromatosis (also common in northern Europeans), can trigger LP/OLP, so get treated for that and treat your liver kindly (watch alcohol consumption; drug use, includings NSAIDS). Get checked for fatty liver disease as well, as that can cause problems. Get thyroid issues (under or over) treated.
The best diet is one that is balanced. The vitamin most associated with autoimmune issues is low Vitamin D levels, so be sure to get enough of that one in particular.
And good luck. Unfortunately, you may do everything "right" and still be afflicted. Life is random and often unfair.