"Having had enough" or "reached a saturation point" can be used as synonyms for the phrase "had a bellyful". These expressions convey a feeling of being completely satisfied or tired of something, whether it be food, an activity, or a person. One can also use the phrase "had their fill" to describe a similar sentiment. These alternative expressions can add variety to one's vocabulary and enhance writing or speaking skills. It is important to use language that accurately conveys one's intended meaning and tone, and exploring synonyms is one way to achieve this.