NEAR HAKALAU, Big Island — Sean Dunckel, a 17-year-old from Napa Valley, Calif., arrived in Hawai'i weighing 248 pounds at 6 feet 2. That made him obese, according to a body mass index measurement.

Three weeks later, he weighs 220 pounds and is looking forward to losing an additional 25 pounds over the next four weeks. That would put him at a healthier 195.

"It's hard work, but it's good," Dunckel said during a break in morning activities at the Wellspring Hawaii weight-loss camp.

Dunckel has joined about 30 teenagers from around the world to shed pounds at the Big Island mountain retreat on the grounds of the Tara Yoga Center, an expansive 40-acre site near Akaka Falls State Park.

Dunckel's mother learned about the camp on the Internet. His own first impression was that "it looks good, and it turns out to be real good. So it's everything that I've been looking for."

The teenager arrived in Hawai'i — his second time to the Big Island — with a mixture of excitement and nervousness.

"You have to be able to put in the work," he said. Dunckel has gone from being unable to do a single pushup to doing at least 10, he said.

It's not easy adjusting to such a rigorous lifestyle, especially considering how many of these campers have spent mostly sedentary lives. He's had trouble with the sleep schedule.

"You only get eight hours of sleep a night," Dunckel said. "It was pretty hard the first week."

The experience is pricey. The four-week session costs $6,950 and the eight-week session is $9,950, although there is a $1,500 kama'aina discount.

Hawai'i kids have attended camps in the past, but this year everyone comes from elsewhere. The 2008 crop includes youths from New Zealand, London, Mexico, Japan, Thailand, Texas, Georgia, New York, Colorado and California.

Last week the camp split into two groups for three days of camping. The trips included soccer games or classic running games like "capture the flag."

Some participants have more trouble adjusting. At least one camper was seen complaining about being homesick and not being able to call his parents.

Aki Morita, the camp's clinical director, said it's challenging for the children to focus on weight loss.

"They are bombarded by fast-food advertisements in their daily lives," Morita said.

Weight loss might also just be one of many problems the teenagers face.

"Kids bring a variety of issues, from homesickness to depression to anxiety," she said. "Some develop medical issues. Some family issues, as well. And my philosophy is to support them whatever their trouble."

The program is run by Wellspring Camps, a group that also runs nine other camps on the Mainland, in the United Kingdom and Australia.

This is the second year for Wellspring Hawaii.