Jamie Oliver looked like he gained weight at the Australian Ministry of Food launch (right). (Getty Images)

Celebrity chef and healthy eating enthusiast Jamie Oliver was on the defensive Tuesday when asked by reporters if he'd put on a few pounds.

"I don't know. I am very healthy," he told Australia's Herald Sun. "Are you from a tabloid? Thank you for noticing, you b***h."

The Naked Chef was down under to launch the first Australian Ministry of Food, a school that offers free cooking lessons and healthy-eating education. But questions about his weight, prompted by pictures of the 36-year-old fresh off a plane and looking slightly puffy, quickly shifted the focus from public health to Oliver's own.

"I do my best," he told reporters. "Working in the food business is quite hard when someone is constantly asking you to try things.

"I eat fresh," he said. "I train twice a week. I could definitely do better, but I am trying to do my best like most people when they hit 30."

According to his U.S. spokeswoman, Kimberly Yorio, Oliver has managed to maintain his weight despite his hectic lifestyle.

"I can say for a fact he hasn't gained any weight," Yorio told ABC News. "They were bad pictures."

Oliver is perhaps most famous for his "Food Revolution," a campaign to curb obesity by promoting healthy cooking in homes and schools.

"Here's somebody who's really trying to pay it forward by going places and trying to right what's wrong," said Dr. David Katz, director of the Yale University Prevention Research Center. "He's looking to advance a public health agenda, and I don't ever recall him saying, 'In order to do that I have to be an underwear model.' I think we get carried away in anthropomorphizing these efforts."

Katz also stressed that Oliver is a chef, not a nutritionist.

"I find it odd that everyone who's ever eaten, cooked or lost weight is suddenly an expert in nutrition," he said. "I don't pretend that because I cook, I'm a chef."

Keith Ayoob, director of the Rose R. Kennedy Center Nutrition Clinic at Albert Einstein College of Medicine in New York City, said eating fresh food and working out twice a week isn't necessarily synonymous with a healthy, balanced lifestyle.

"Even if you're eating good food, you can still eat too much," he said. "It comes down to excess calories, from too much food or too little exercise."