It has the second highest per capita gross domestic product in the world and the third largest proven reserves of natural gas. But it also ranks high in some less enviable categories, having among the greatest prevalence of obesity, diabetes and genetic disorders in the world, according to international and local health experts.

Native Qataris, who number only about 250,000 in a nation of 1.6 million, are suffering serious health problems that relate directly to a privileged lifestyle paid for with the nation’s oil wealth, as well as a determination to hold onto social traditions, like having young people marry their cousins.

“We’re talking serious obesity,” said Dr. Justin Grantham, a specialist at Qatar’s orthopedic and sports medicine hospital involved in a healthy-living pilot program. “The long-term health consequences will be significant.”

Like other oil-rich nations, Qatar has leaped across decades of development in a short time, leaving behind the physically demanding life of the desert for air-conditioned comfort, servants and fast food.

While embracing modern conveniences, however, Qataris have also struggled to protect their cultural identity from the forces of globalization. For many here, that has included continuing the practice of marrying within families, even when it predictably produces genetic disorders, like blindness and various mental disabilities.

“It’s really hard to break traditions,” said Dr. Hatem El-Shanti, a pediatrician and clinical geneticist who runs a genetics testing center in Doha, the capital. “It’s a tradition carried from one generation to the next.”

Qataris live in a nation no larger than the state of Connecticut where they are a minority among the more than a million foreign workers lured here for jobs. But their problems are not unique.

Kuwait, Bahrain, the United Arab Emirates and Saudi Arabia all share similar struggles with obesity, diabetes and genetic disorders, each suffering the side effects of an oil-financed lifestyle and a desire to hold on to traditions.

Yet, even in this neighborhood, Qatar stands out.

According to the International Association for the Study of Obesity, Qatar ranks sixth globally for prevalence of obesity and has the highest rate of obesity among boys in the Middle East and North African region. A recent article in the Qatari newspaper Al Watan said that local health experts predicted that within five years, 73 percent of Qatari women and 69 percent of the men would qualify as obese.

Obesity is considered the most important factor in the development of diabetes and is a prime contributor to many other ailments, like hypertension. The International Diabetes Federation ranks Qatar fifth globally in terms of the proportion of people aged 20 to 79 with diabetes.

The March of Dimes Foundation, a United States charity that focuses on trying to wipe out birth defects, listed Qatar as 16th globally for the incidence of birth defects per 1,000 live births. The chief cause of the problem in Qatar is consanguineous marriages, experts here said. Saudi Arabia ranked second globally.

For all of these challenges, and for all of its wealth, Qatar has primarily focused on the treatment of diseases rather than on prevention.

Everyone here points to lifestyle and tradition to explain the nation’s health crises. While it was once taboo to talk about the problems involved with marrying relatives, they are now talked about openly. There have been some discussions about premarital genetic screening, or genetic testing done at birth. But the tradition is so strong, no one has raised the prospect of curbing it.

“You can’t tackle the issue,” said Moza al-Malki, a family therapist and writer. “There are some big families, clans, they don’t marry outside the family. They won’t allow it.”

The issue of obesity seems to run into the same wall of tradition, health experts here said.

“If you don’t eat, it’s considered a shame, and if you leave someone’s home without eating it’s a shame,” said Abdulla al-Naimi, 25, who refers to himself as “chubby” but is noticeably overweight. “Half of my family has diabetes,” Mr. Naimi said. “My mother has diabetes. Three cousins younger than me have diabetes. For me, I eat too much and I don’t exercise.”

He is also married to his first cousin.

And Mr. Naimi happens to be the project director for the Healthy Lifestyle, a fledgling effort to try to shift from treatment to prevention. It is connected to the Qatar Foundation, founded by the emir of Qatar, Sheik Hamad bin Khalifa al-Thani. Mr. Naimi sees no irony in all this because in Qatari terms, his weight and his choice of a relative as a spouse are the norm, he said.

He acknowledges that changing attitudes will be a slow process, at best. “We are trying to change people’s habits, just to get them to walk,” he said, admitting that he himself never finds the time to exercise.

Walking is not popular in Qatar’s heat. Average high temperatures in June and July are a very humid 106 degrees, and Doha, like many cities in the region, is not built for pedestrians.

To make matters worse, people here said that all of their social occasions were defined by eating. Traditional meals usually include rice, clarified butter and lamb. Because people often share large community platters, there is almost no way to keep track of portion size, people here said.

“We can’t get together and not eat,” said a 22-year-old Qatari woman who is a member of the Thani royal family. She asked that her name not be used to avoid embarrassing her immediate relatives.

She said her family was typical. Of seven children, five had weight problems. One brother hit 265 pounds by the time he was 19. A younger brother, who is 10, weighs 125 pounds and is gaining weight so fast that he no longer fits in pants she gave him two months ago.

She said the typical Qatari student skipped breakfast, then ate a snack and lunch at school. When students return home they are given another lunch, generally a heavy meal of rice and lamb. Later, they snack on cake and tea. And then at night they eat dinner, often fast food that is delivered.

“I eat lunch, then I go visit a friend; I am so full, but they put a table in front of you and keep bringing food,” she said. “I cannot eat, but it’s an insult.”

Another more challenging problem, is attitude, said Nelda Nader, a dietician here. “For the majority,” she said, “it is really quite normal to be obese.”