In the past, only celebrities and the super wealthy could afford a personal trainer, private chef and inspirational guru. Now the rest of us can have diet coaches in our back pockets—literally. Otherwise known as health and fitness apps, these secret weapons are hot: There was a 19 percent increase in new apps in the last year alone, according to the mobile analytics platform Localytics.

"Newer apps are far more engaging, motivating and user-friendly than the prior generation," noted Bonnie Spring, director of the Center for Behavior and Health at Northwestern University Feinberg School of Medicine. And they work. Experts say that dieters who include apps in their weight-loss efforts score greater success than those who don't. We asked three Health readers to each test a leading digital diet and report back. See how the tools helped them and what they can do for you. 16 Ways to Lose Weight Fast