Hi Holly! How great that you're nursing your 20 month old.
It seems many mothers wean too soon these days.
As your body loses fat, it also releases all of the toxins stored in that fat. When you are in ketosis, nearly everything that you are burning is fat, so the amount of toxins being excreted is high. While in general this is a good thing, don't forget that the toxins will be excreted via all bodily fluids, including breastmilk. It is not dangerous to you if you breastfeed while in ketosis, however, it may be dangerous to your developing baby.
I see your point when you say that you are not nursing a newborn and therefore may not need to follow the same guidelines. I agree with you to some extent. There is a point when you are nursing a toddler (or young child) when you have to resume your life!
I personally made the choice to do Induction when my nursling was 2 *but* she was nursing only 1-2 times per day for no more than 10-15 minutes total per day. She has commented many times on the change of the taste of my milk (she says it's sour like lemons) - one of the "benefits" of having a nursling whose third birthday party I'm in the process of planning.
A younger, less verbal child might simply start to push away from nursing due to the change in taste, resulting in an earlier weaning than you anticpated.
You mention that she's nursing 5-6 times per day, plus throughout the night. Most people in the West consider that to be full-time nursing at newborn levels. I don't mention this fact because I agree with it (because I most emphatically do not think that only nursing 6+ times a day is sufficient for a baby under a year old) but rather because researchers are looking at this amount of nursing when they make recommendations.
I have been where you are now and I may even know how you feel right now. You sound like you want to nurture your child in the best way possible, but you are probably also tired of carrying extra weight. I think you can have what you want, but you might not be able to have it as quickly as you were hoping. You might find that it is best to settle for a slower weight loss whilst preserving your breastfeeding relationship with your daughter.
If I was in the same situation (which I am not, so feel free to ignore me!
), I would switch plans to something that is low carb without encouraging ketosis until your nursling is older. I would not wean - not that you're seriously considering it. The long-term benefits of breastfeeding to both you and your growing child are greater than any benefit derived from losing weight more quickly. I would tweak the carb levels in my diet so that I was losing no more than 6-8lbs a month. I wouldn't up my carb levels with pizza, but I would definitely add more vegetables and allow more carby veggies like tomatoes, carrots, low-glycemic fruits, and maybe even the odd bit of corn.
Again, as I pointed out earlier, this is what *I* would do, not what you should necessarily do. This is your choice that you need to make for both you and your daughter. I wish you all the best as you make your decision.