Did a little bit of tax research and it appears that not many could possibly deduct this, even if it could be made a legit deduction. See this article
here.
First it appears the doctor would have to declare you "obese", not just overweight, as "obesity" is the medical condition that is being treated. I'm not sure how many pounds over the norm that has to be, but I know 10 or 20 extra pounds isn't going to put you into that category (unless your doctor is really leanient).
Secondly this would get lumped into your other "unreimbursed medical expenses", and you have to have enough of those to be over 7.5% of your adjusted gross income. This would exclude a lot of people, myself included, as I don't have lots of big medical bills.
The article (and other sources I looked at) never mention if "exercise equipment" as being deductable or non deductable. They all say the unreimbused costs of a "weight loss program" are deductable. I image that might include equipment, but I can't say for sure.
Anyway, it looks like most of us wouldn't be able to do this, but maybe there's someone out there that still could.