I have had days where I ate NOTHING and had a gain on the scale the next day. (I don't make a habit of eating nothing, it just works out that way on occasion.) By the same token I have had days when I ate way more than my normal calories and had a loss the next day. Unfortunately there aren't as many of those
Looking at my daily weigh in chart helps keep the long term progress in focus. There are lots of ups and downs but that trend line is still pointing down.