Actor Jonah Hill sheds weight and looks great — what’s his motivation?

The former chubster has slimmed down considerably. He allegedly did it the old-fashioned way: diet and exercise. He follows in the footsteps of funny former male fatties such as Seth Rogan, Horatio Sanz and George Lopez, who have all noticeably trimmed their waistlines.

There will always be those who fear that once a comedic fat person slims down they’ll no longer be funny, as if their talent and humor were inexorably tied to their adipose tissue. While Internet commenters speculate on whether Hill will retain his wit, we ran across this sane comment left on the Huffington Post website: “Good for Jonah Hill. He will have a happier healthier and hopefully long life. He was funny as an overweight guy, but has the talent to shed that image and go on. Good for him.”

We know what you’re thinking: Actors have it easy. Not only can they afford the best personal trainers and nutrition advisers, but they have built-in motivation, usually in the form of a movie contract and a hefty paycheck.

Motivation is essential to staying with a program, but the rich and famous don’t have a lock on it. A 2010 study in the Journal of Nutrition Education and Behavior looked at how motivation affected sticking to a weight-loss plan and losing weight. Researchers followed 66 women ages 22 to 65 who took part in a 16-week Internet behavioral weight-loss program.

Those whose motivation was self-directed were more likely to do better in the weight-loss program, and those who were self-motivated at the fourth week of the study did better at losing weight over the 16 weeks.

Many fitness experts say that the best motivation comes from within — a desire to look or feel better, wanting to be alive to see kids grow up — rather than from without, such as feeling pressure from a friend or family member.