The IRS now recognizes obesity as a disease, so if your main purpose is to prevent or alleviate obesity, health club membership fees may be deductible as a medical expense under Sec. 213. 

However, IRS will carefully scrutinize each case, denying the fees if a health club closer to home would work just as well, or if the taxpayer could exercise safely without joining a health club.

Source: BNA Tax
        August 19, 2002