Though he has a few billion houses to visit, Santa Claus should get off his sleigh and walk or bike, according to a cheeky public health doctor, who says Santa’s commercial image promotes obesity, unsafe air travel and a general unhealthy lifestyle.

“His popularity should be used to promote healthy living,” Dr. Nathan Grills argued in a light-hearted “analysis” in the Christmas issue of bmj.com.

In 2007, acting U.S. surgeon general Steven Galson declared Santa should be thinner. Now Grills is urging Santa to lose his belly fat (the most dangerous kind), to eat carrots instead of energy-dense cookies and to don a helmet while participating in “extreme sports such as roof surfing and chimney jumping.”

“Given Santa’s fame, he has considerable potential to influence individual and societal behavior — and not necessarily for good,” Grills wrote in the satirical piece. “I am suspicious of how he has been co-opted for marketing purposes.”

Santa’s rotund image, popularized by 1930s ads for Coca-Cola, is a far cry from the original St. Nick, who was quite trim. And though his quivering belly has been associated with joviality, it’s a mistake to equate obesity with cheerfulness, according to Canadian researchers who found that “remaining sedentary was generally associated with a low jolly quotient.” (Yes, Virginia, they actually study this stuff.)

But Frankfort, Ill., physical therapist Vincent Gutierrez worries that if Santa were skinny, he might not have enough energy to perform his duties. He needs “a huge resource of fat in order to perform what is, quite frankly, the greatest endurance activity known to man: Carrying and delivering presents throughout the entire world,” Gutierrez wrote in a heated Facebook discussion.