For two weeks, it has been staple in my daily diet. Sometimes I eat more than two bananas in a day. So to make sure I am doing the right thing I ask how many calories is in a piece of banana and here's what I read;
An extra small banana ( up to six inches) has 75 calories while a small one (six and seven inches) has at least 90 calories. There are 105 calories in medium bananas (seven and eight inches in length)
Source : calories in banana
So I think having two or three extra small bananas in a day is okay if you'll only count the calories however you might want to check also the carb and the sugar because bananas is not included in the list of low carb fruit.