Can you eat bananas on an empty stomach ?

There's no obvious reason that a healthy person should absolutely not do this. One caution I'd give is that bananas can increase blood sugar a little more than many other fruits, and having them on an empty stomach (or just not in conjunction with other foods that contain protein and fats in general) can make this effect can be a little more pronounced. Most people who eat bananas are eating them in the morning, which is a time when many people are more prone to blood sugar spikes and crashes for a variety of reasons. So bananas aren't a fantastic standalone breakfast choice in terms of keeping your mood and energy nice and even. And for people with insulin resistance or diabetes, this is even more of a concern. Some diabetics really can't eat any carbs in the morning, even if it's balanced with protein and fats. But for most of us, a banana is fine--morning or otherwise. Unless you're looking for some specific effect of eating a banana by itself, like maybe for athletic performance, a morning banana should generally be coupled with some protein and healthy fats at the same time or within 30 minutes or so.