Is gestational diabetes caused by diet or some are at higher risk due to family history?

Both plays a part. There is not really a who is a bigger part but if u have it in the family, higher chance of u getting it. Even if u don't have it in the family, poor food choices will cause u to have gestational diabetes too. Gestational diabetes run in my family but I was ok all the way. So watch what u eat, make the calories count by eating nutritious food in moderation ya. If eat for 2, almost surely u will have it