Three bananas a day is a bit much but bananas, in moderation, are still healthy.
"For most people with diabetes, fruits (including bananas) are a healthy choice. One exception to this is if you're following a low-carb diet to control your diabetes. Even a small banana contains around 22 grams of carbs, which may be too much for your diet plan."
I have never heard that Consumption of sugar in and of itself, can cause diabetes.
"Consuming sugar is not a direct risk factor for type 2 diabetes, although it can have indirect effects, such as weight gain, that make the condition more likely to develop. Risk factors for type 2 diabetes include: being overweight or having a large waist circumference."
Although my mother-in-law believed that if she ate a piece of hard candy a day, she would never develop diabetes. She didn't, so I guess it worked for her.
The men in my family all have type II diabetes. Most of them are on insulin, but the rest of them (including the women) control it with diet and medication.
I myself, eat a quarter or a third of a banana a day, depending how big the banana is. I got a banana slicer from Amazon that cuts it in 6-1/4 inch slices. I put six slices a day on my waffle with a smear of peanut butter. The peanut butter and waffle are worse for my diabetes then the banana is. I don't worry about it because I weigh less than 100 pounds. I take metformin with dinner which keeps my blood sugar level and my A1c is within normal limits.
When I was in the hospital and rehab, they did not give me any medication, but tested my sugar before every meal. The two or three times it went up over 160 I got a shot. Otherwise, the doctors and nurses were happy if I tested 120 to 130. They were unhappy when I dropped below 100 and made me eat.
When I got home, I tested my sugar before breakfast and it was up over 190 every day. I went back on Metformin but it didn't seem to help. Then I noticed my testing supplies were at least a year out of date. I spent $90 on a new machine and my levels dropped to normal.