I’ve gotten too lean- does that mean I should start adding grain back in?
While you're right to think of grain as the first choice to pack on weight (think about what is fed to cattle in stockyards to fatten them up- GRAIN or added into commercially available pet kibble as a filler- GRAIN), getting too lean while following THE PALEO DIET doesn't mean it's not a good fit for you, or that you should deviate and resort back to food-stuffs that we know are not good to consume.
What's the answer, then?
Adding some food with more caloric density- as in healthy fat, will help get you back to a healthy weight if you've gotten too lean.
I experienced the same thing; when I weighed in at 113 pounds at 5'6", I began receiving (concerned) comments from clients and friends, asking if everything was OK, and was I eating! (If only they knew how much I eat! : ). However, I did agree I was a bit too lean, so over the course of the next several weeks, I added a bit more coconut oil, flaxseed oil, olive oil and avocado to bring me up to 116 pounds, where I've remained for the past three years.
Many people might say think it's an odd thing to be concerned about, when the majority of the population has exactly the opposite problem, so I bring this to their attention if there's any doubt that eating PALEO foods promote the body to get to a healthy, lean weight.
As always, it's about finding the balance between calories in versus calories out (including exercise expenditure). You'll know you're at a healthy weight when you're energy levels are great, you're sleeping well and your eating is supporting your training.
Use how your body feels as the ultimate guide for whether or not you're where you should be and adjust accordingly!