Can someone explain to me what milk thistle does for NBE?
Also does anybody know if it is safe to diet or such with NBE?

Milk thistle is a liver cleanser, it protects liver against oxidative damage and stimulates its regeneration. A healthy liver is very important for NBE, cause herb substances convert into useful forms in the liver, also liver gets a bit 'worked up' with herbs in the long run and needs some support. I do not understand your second question though. It's advisable to include milk thistle into a NBE routine, but in small ammounts or only in certain times, to not take it all the time, as it may cause hair loss.

is it safe to lose weight and exercise while doing NBE? Is there any damage done if you lose weight?

Also, be weary about taking it if you're on birth control. According to DrugDigest.org, "Milk Thistle may interfere with the effectiveness of estrogen by blocking an enzyme that breaks down estrogen in the body. As a result, estrogen products may not be as effective... in addition, oral contraceptives may not be as effective and an unintended pregnancy could result."

Damage, no. But it's not advisable to loose weight and do NBE at the same time, as you might as well loose it from your boobs.