Particularly with the heavy thirst of breastfeeding you do want to be sure you have plenty of fluids so DO listen to your thirst, but yes, you will likely be better off drinking pretty much anything but water. I drink LOTS of whole milk and some juice.
Any yes, these ideas can help the overweight as well as the underweight. I’ve been following these idea since I conceived this spring and I’m due in three days. I started out at my highest weight ever and I’ve gained a lot of weight this pregnancy, but I’ve also seen a lot of improvement some very long term symptoms. I’m hopeful that once the baby is here my body will be comfortable releasing some of this weight as long as I keep taking care of it.