I have seen this w/o breaks 5-7 interviews a day, too often. Some candidates suffer from low energy at the (n-1)th interview. The interviewer is baffled and gives a slightly negative feedback. The reason for the interviewee's interaction is not the skill of the interviewer.
So, in short - please keep breaks. You should have a 1h (min.) dedicated lunch break if you have a long 1-day interview. In additional, you should schedule 15m breaks in the morning and afternoon session to let the candidate recuperate. Finally, please ask your interviewers to look through the candidate schedule. Take into account that they have had many interviews, do your bit to make them comfortable. Also, please do not spin this as "If you can't go without breaks in a 7h day, you are not good enough to work here". Kindness, empathy helps and makes you a better employer.