Re: Why does having smoothies raise your blood sugar
I'm not sure I understand your question, as far as the part about making you tired goes.
Yes, fruit is good for you. Most fruits contain lots of phytochemicals that are nutritious and great cancer-preventing substances. However, both fruit and yogurt (which is usually in smoothies) contain carbs, and any type of carbs will raise your blood sugar.
You didn't say exactly how high your blood sugar goes after downing a smoothie. One usually doesn't feel the tiredness of high blood sugars until they get quite high, usually over 200, although that does vary from individual to individual. Also, your bg may rise more slowly with a smoothie than if you ate something like a cookie, and the slower increase may also prevent that feeling of exhaustion that can come about after eating a lot of carbs.
Hope I've answered your question...feel free to post back and further clarify the question if I've missed the point!