Even though your question is a simple one it’s actually a very good one. Sometimes the BF% does go up and it can be related to a various reasons. Personally, I’m not that concerned if this happens once in a while because that is part of being human and life doesn’t always goes as planned. Stress, illness, work, family, etc. can have an effect on someone’s life that can lead to poor food choices or lifestyle. If it’s a pattern that is constant, then I have to look into my client’s lifestyle more closely and figure out what is going on and try to find a way to help them fix it. I like to see things from a wider angle and not neat picking every negative fact in their life. I tell my clients not to worry to much about it and try to stay focus on their overall fitness improvement that includes their lifestyle, diet and mental health.