Going to the gym is about to get a lot more expensive. That's because the share of companies offering wellness programs dropped 13 percent this year. These programs -- which often include subsidized gym memberships, free fitness trackers, and bonuses for losing weight -- keep employees healthy, thereby cutting medical and insurance expenses. At least that's the theory.

In practice, many companies aren't seeing a return on their wellness investments. So they're ditching the programs. That's a mistake. Employers can save themselves millions through wellness programs. They just need to find ways to boost workers' low participation rates.