That's true if we're talking about fruit juice. I say stay away from fruit juice. The sugar is too concentrated. So don't blend up fruit with juice, use soy or rice milk. Also, don't blend up a banana. Eat a small or a half banana at a time, or, as you say, an almost ripe one. Also, stay away from dried fruits. Sugar's too concentrated. But a handful of berries is not too sweet and the blender doesn't break down the sugar into simple sugars because fructose (fruit sugar) is already simple. Only stomach enzymes can change their chemistry. But you're still getting the fiber and skins and seeds in the whole fruit when you blend it and that helps control the blood sugar levels. Also, if you add some coconut oil or protein powder into the shake, it slows down the rate the sugar is absorbed in the stomach. I also recommend fruit powders, which have had the sugar removed. I have at least 2 fruit smoothies a day, plus at least 7 servings of whole fruit, and I test my blood sugar levels constantly. My levels remain constant. Now, if you have diabetes or pre-diabetes, than you need to be more careful.
As for your high heart rate, it can be coming from your walks, you could have a food allergy (you said your pulse is taken after lunch), dehydration can cause it, stress, hyperthyroidism. 100 is about the high limit before you should start being worried. As long as you don't have symptoms, like headaches from it, it shouldn't be a problem. I would just recommend eating right. Less animal fats, less sugar, more vegetables. Omega-3 fish oil. Aerobic exercise. Relaxation techniques.