I have gone from 215lbs to 178lbs in 10 months for no apparent reason?

I don't know what's the matter. Nothing in my lifestyle or diet has changed. I have dropped from a 38in waist to a 34in. I have been to the doctor and had a blood tests and they al came back clear. I have no idea why or how I am losing this weight? Anyone have any ideas?
I have gone from 215lbs to 178lbs in 10 months for no apparent reason?
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