I did notice that a little bit on really hot days (90 degrees). I asked my pedi about giving LO water on hot days to keep her hydrated and he told me that she will take what she needs in formula. I know I tend to eat less on really hot days so as long as your LO is getting enough breastmilk or formula for the day, I wouldn't worry. At this age, the nutrition is in the milk anyhow.