Actress Emma Watson, who played Hermione Granger in the “Harry Potter” series, compares her social media use to counting calories.

“It's so important to keep an eye on what your daily diet is,” she explains. “In the same way we think about what we eat, we should think about what we read, what we're seeing, what we're engaging, and what we're interacting with every day.”

That may seem elementary, dear Watson, but that simple truth is something many folks seem to have overlooked.

Research has shown that spending too much time on smartphones can trigger insomnia and depression. But did you know that smartphone overuse also contributes to obesity?

A study presented at the American College of Cardiology Latin American conference found that being on your smartphone for five-plus hours a day boosts your risk for obesity by a hefty 43%.

Why? Because it dramatically increases sedentary behavior and the inclination to snack on fast food and sugar-added treats and beverages.

To help shed excess weight, try this smartphone diet:

• At night, leave your phone outside the bedroom.

• Uninstall your stickiest apps. Can't stop playing games or posting pictures? No more CandyCrush or Instagram.

• Use your phone to get moving. Download a pedometer with a step reminder. Attend a video yoga class. Set a “Stand up!” alarm that goes off every 30 minutes, then run in place or walk the dog.

• If all else fails, invest in a “dumb phone” that only allows you to call and text. Ironically, that may be the smartest move of all.