Last year, Soonsik Kim threw out her skinny jeans. The 50-year-old, who goes by "Sara," had kept them for more than a decade, hoping that, someday, she'd lose the 30 pounds she gained after moving to the U.S. from South Korea and squeeze them back on.

That day never came.

"I gave up my hope," says Kim, who lives in Cresskill, New Jersey, and runs the Korean Community Services of Metropolitan New York's Public Health and Research Center.

But at 5 feet 5 inches and 140 pounds, Kim is still more than 25 pounds lighter than the average American woman and has a body mass index of 23.3, which fits her squarely in the "normal" weight category. In a country where more than two-thirds of the population is overweight or obese, that's often considered something to be proud of.

"My Korean friends always comment that [I] don't look heavy," she says. They ask why she is concerned about her weight. Her American friends, meanwhile, tell her she's "so skinny."

Soonsik "Sara" Kim worries about her weight because she knows Asians suffer from conditions like diabetes at lower BMIs than other populations.

(Courtesy of Soonsik "Sara" Kim)

But Kim, who weighed a steady 110 pounds for most of her adult life in South Korea, knows that looks can be deceiving. Her doctor told her that her A1C levels – a measure of diabetes risk – are slightly elevated and not budging. "[It's] really frustrating me," she says.

While only 11 percent of Asian-Americans are obese, they develop obesity-related complications – namely, hypertension and diabetes – at lower BMIs than do people of other backgrounds, research shows. The American Diabetes Association, for one, recommends that Asian-Americans get screened for diabetes if their BMIs are 23 or higher, versus the 25-or-higher guideline for the rest of the population. The World Health Organization also proposed lower BMI cutoffs for determining overweight and obesity in Asian populations in 2004, but experts say it's unclear how widespread or practical their use is. What is clear? The fact that if more obesity statistics took into account different cutoffs for different populations, the picture of Asian and Asian-American health might look a lot different.

So would Kim's. By the WHO's measures for Asian populations – which define overweight as a BMI greater than 23 (compared to 25) and obese as 27.5 (rather than 30) – she's considered overweight.

"The educated [Asian] population knows that they're getting diabetes and hypertension and all these things at a much lower BMI, but if you're in a culture where everybody's really fat and you're thin, you tend to go around and think, 'Well, I'm protected,'" says Dr. Michael Jensen, an endocrinologist at the Mayo Clinic in Rochester, Minnesota, who studies how body fat, and its distribution, influences health. "But [you] may not be."

"We assume that all human beings are designed the same way – the same shape, the same body proportions and so on, and I think that's a huge oversimplification," says Dr. Steven Heymsfield, a professor at Louisiana State University's Pennington Biomedical Research Center, where he studies obesity. "We're just in the early stages of understanding how things like BMI relate to things like risk of obesity and diabetes, but there's a lot more to come."

The (Un)luck of the Draw – or Something Bigger?

Why do Asian-Americans seem to have a lower threshold for what's considered overweight, and more problems at lower BMIs? "It's complicated," says cardiovascular disease epidemiologist Stella Yi, an assistant professor in the New York University School of Medicine's Department of Population Health who studies Asian-American health disparities.

For one, she says, the population tends to have more body fat than people of other racial and ethnic groups with the same BMI. So, just as BMIs can wrongly label people who are muscular as overweight or obese, they can deceivingly categorize people with unhealthy amounts of fat as normal. That appears to be especially true among Asian populations.

"It kind of ties together all with the fact that BMI is a faulty measure – it doesn't account for the proportion that someone is of lean muscle mass versus fat," says Yi, whose paper published last year in the journal Preventive Medicine points out that obesity prevalence statistics of Asian-Americans aren’t derived from WHO-adjusted BMI cutoffs; they don’t differentiate between subgroups of Asian-Americans; and they don’t account for the constantly growing and changing nature of the Asian population in the U.S.

Where Asians carry their weight matters, too. While Caucasian and Hispanic populations often get bigger all around or on their hips and legs before developing belly fat, Jensen says, Asians tend to collect excess weight around their middles – a well-documented risk for obesity-related complications such as heart disease and even early death.

"If you're Asian-American and, even if your BMI is OK, but you're getting a big gut, that's a bad sign," Jensen says.

This phenomenon can also be traced to a cellular level, Jensen says. He points out that, likely due to some combination of genetic and cultural factors like the mom's diet during pregnancy, Asians' fat – or adipose – tissue seems to have "a limited capacity" to expand and maintain normal function during weight gain. As a result, the population experiences obesity-related complications at lower BMIs than their counterparts of other backgrounds whose bodies are better at handling expanding fat cells.

"This adaptation, if that’s what it is, is really good at protecting you from starving," Jensen says, "but it’s really bad at protecting you from overeating."

Then, there's the bigger picture: environmental and cultural factors. Take physical activity. Asian-Americans have some of the lowest rates of physical activity of any racial or ethnic group in the U.S., research suggests. "Asian-Americans are not exercising – and this is across the life course," Yi says. "Then, all of a sudden, they turn 60, they retire and they start doing tai chi, and so then everyone is kind of under the impression that, ‘Oh, of course Asian people are exercising because I see the Chinese people doing tai chi in the park."

But that emphasis on physical activity doesn't begin early enough. Instead, many Asian-American kids are inactive in part because their cultures value academics over sports, Yi says. "It sounds terribly stereotypical … but that's the reality," she says. "There are no norms around physical-activity behaviors in Asia and in Asian-Americans."

The "model minority" stereotype – or the perception that Asian-Americans are highly educated, wealthy and, yes, thin – may also play a role in Asian-Americans' rates of what researchers call "metabolic obesity" – aka skinny on the outside, fat on the inside. "Because of … the idea that Asian-Americans are healthy, wealthy and wise … even when parents see their children kind of getting chubbier, they kind of ignore it," Yi says. "They're like, 'Well, we're the model minority, my child is fine.'"

Diet, of course, matters too. Research suggests that immigrants are turning to special-occasion foods – namely, those high in carbs, fat, sugar and animal protein – on a regular basis. And, in families where grandparents care for the kids – a common setup in Asian cultures – the elders often spoil the children with food treats, Yi says.

For Kim, who ate mostly rice and vegetables in South Korea, the accessibility of fast food in the U.S., combined with a teenage son who wants to eat it and a lack of time and money means she picks up Burger King or Wendy's once or twice a week. Meat is also much cheaper in the states, she adds. "I thought that when you go to move to the U.S., we will get heavier and heavier because of junk food and a lot of fast-food restaurants in our neighborhood," Kim says. "What I thought was true."

Trading White Rice for Brown

Fortunately, there's a movement afoot in the U.S. to boost awareness of these issues in Asian communities and to intervene in culturally appropriate ways. After all, Asian-Americans are the country's fastest-growing ethnic group – and their rates of obesity are rising fastest as well, statistics suggests.

"Even though Asian-Americans and Native Hawaiians and Pacific Islanders aren't part of the national narrative [on obesity] … our communities do know that this is something that we have to prioritize," says Pedro Arista, a program manager at the Asian and Pacific Islander American Health Forum, a health justice organization with offices in San Francisco and the District of Columbia.

For instance, one of his organization's grantees partnered with churches, schools and recreation centers in Salt Lake City – where the Tongan population has high rates of childhood obesity, diabetes and other noncommunicable diseases – to offer Zumba classes and other healthy living activities. Arista is also working on an initiative that aims to make Los Angeles' Chinatown more walkable, as well as others that teach Asian-Americans about nutrition.

"When we’re talking about healthy eating, we’re just not talking about more generalizable fruits and vegetables, but we’re also talking about brown rice, we’re talking about bok choy, we’re talking about taro," he says. "We’re talking about fruits and vegetables that are connected to our cultures and our identity."

Kim's work to tailor health interventions to Korean communities in the greater New York area takes a similar approach. She helped implement a campaign that encourages people to choose brown rice over white rice, for example; she is working to reduce sodium levels at Korean restaurants; and she helped bring hypertension screenings to largely Korean churches.