I known of this one...from Turkey.
"Ramadan fasting had no significant effect on the macronutrient composition of the breast milk and consequently the growth of the infants. There were significant differences in some of the micronutrients such as zinc, magnesium and potassium. The nutritional status of lactating women was affected by Ramadan fasting. All of the nutrient intakes (except vitamins A, E and C) decreased during Ramadan. For these reasons, it would seem prudent to excuse lactating women from fasting during Ramadan."
There's also this:
Honestly, as Ramadan is occurring during summer this year, I think you have to be even more mindful of dehydration (both for pregnant Mamas and breastfeeding Mamas.) The pressure in some countries to fast even when there is an exemption can be a lot to handle. I know one Mom who fasted from food, but not water, when breastfeeding because she said she felt like she was still "part of the fast", but it wasn't as risky as no water. She knew that Allah(swt) might not accept it too. I think she paid for a hungry person to eat as well.
For me, I usually have not fasted when pregnant or breastfeeding because I've had issues with dehydration before (both pregnant and not), although this year...I'm kind of at the end of breastfeeding...so I'm not sure what I'll do. I might do what my friend did and keep drinking the first few days and see how that goes...and if O.K....experiment with no fluids either. I really don't know. :)