I am curious about people with HIT (Histamine Intolerance). Typically we avoid leftovers, because they have more histidine in them. Do you agree with this?

Yes, our general rule of thumb for those with Histamine Intolerance is to avoid leftovers older than 48 hours. However, you may try adding in colostrum early in your program, and within about 3 weeks your system might be strong enough to handle more foods than you are used to.