Thin Asians could still be at risk of diabetes due to hidden body fat

February 12, 2013

Istanbul, Turkey - Type 2 diabetes, usually associated with obesity, can occur in many seemingly thin people from ethnic minorities, doctors told attendees at the Excellence in Diabetes 2013 meeting last week[1].

Researchers showed that Japanese American women are twice as likely to be diagnosed with diabetes as whites, despite having lower body-mass indexes (BMIs). Epidemiologist Dr Gertraud Maskarinec (University of Hawaii Cancer Center, Honolulu) presented the findings, which cover a number of studies from her group, in a poster.

Just because they don't look fat doesn't mean they are healthy.

She said an in interview: "Diabetes risk is higher in all ethnic groups than in whites, and of course some of this is just due to body weight, but evidence is now building that people of many races may be at increased risk of diabetes and cancer before they are even considered conventionally overweight."

In communities where there are a lot of Asians, "I think it's on everybody's radar already," said Maskarinec. "If an Asian walks in, you don't have to wait until they weigh hundreds of pounds to do a diabetes test." The World Health Organization has worked on the idea to lower the "at-risk" BMI to 23 for certain ethnic groups, she adds, but "not everybody has adopted it."

Meanwhile, Dr Chittaranjan Yajnick (King Edward Memorial Diabetes Unit, Pune, India) also gave a talk on what makes Indians so susceptible to diabetes. "We have seen that Indians are often diagnosed with diabetes 10 years earlier and five- to 10-units BMI thinner than whites," he noted.

Both believe the explanation lies in "hidden" visceral fat found inside the body, between organs, in Asians and probably other ethnic groups too, but not in whites. This is turn affects the levels of adipokines secreted, such as leptin and adiponectin, which can have adverse metabolic effects.

Japanese Americans: Much more visceral fat than whites

The knowledge that Asians and other ethnic groups are at much greater risk of diseases associated with obesity, such as diabetes and many cancers, than whites, is not new, Maskarinec explained. But more recently, researchers have begun to show that nonwhites who are not even particularly overweight or who are of "normal" weight are at much higher risk than whites. "People have talked about some kind of adaptation for white people, who have had a greater number of years to adjust to the type of food we are eating now," she postulated.

As part of their research, Maskarinec and her colleagues used the Hawaii component of the Multiethnic Cohort (MEC) to examine the influence of BMI on diabetes incidence.

They measured leptin and adiponectin by ELISA assay in 312 ethnically Japanese and 208 white women. Magnetic resonance imaging (MRI) and dual-energy X-ray absorptiometry (DXA) were performed in 30 white and 30 Japanese cohort members.

Overall, Japanese women had significantly lower BMIs (23.7 vs 25.3 kg/m2), leptin (15.0 vs 25.9 ng/mL), and adiponectin (11.7 vs 16.0 ìg/mL) than whites (p<0.0001 for all).

But in adjusted models, Japanese were twice as likely to be diagnosed with diabetes as whites across all BMI categories: <22 kg/m2, 22.0 to 24.9 kg/m2, 25.0 to 29.9 kg/m2, and >30 kg/m2.

The DXA and MRI scans of the 30 white and 30 Japanese women, published in 2011, showed much more trunk fat and percentage of abdominal visceral fat in the Japanese than in the white women[2]. Japanese women had higher trunk-to-peripheral-fat ratios and a greater percentage of liver fat and were twice as likely to have fatty livers as whites, the data showed.

The adverse effects of visceral fat and/or patterns of adipokines may be responsible for the higher diabetes risk in Asians.

"Greater central adiposity reflecting the adverse effects of visceral fat and/or patterns of adipokines may be responsible for the higher diabetes risk in Asians as compared to whites at the same BMI level," Maskarinec and colleagues concluded.

Maskarinec also showed data on DXA whole-body scans obtained for 101 adult women (>30 years) and their 112 daughters (age 10 to 16 years) in Hawaii, divided into all white, mixed of non-Asian descent, mixed of partly Asian, and all Asian, taken from another study by her colleagues published last year[3]. These results confirmed previous reports of greater central adiposity in women of Asian ancestry and indicated that ethnic differences in adiposity were already present in adolescence.

Maskarinec said ethnic differences in body-fat amount or distribution that develops early in life may be key, with some scientists believing the intrauterine environment plays an important role, although this latter concept is still just a hypothesis, she stressed.

So could it be epigenetics?

Yajnick is one such proponent of this theory: "All the risk factors for diabetes and adiposity, including blood chemistry, are present at birth," he told the meeting. His research includes evidence that Indian babies "are small but adipose; it's all about nutritional programming rather than the birth weight."

If an Asian walks in, you don't have to wait until they weigh hundreds of pounds to do a diabetes test.

Susceptibility to noncommunicable diseases such as diabetes "is thus not only genetic, but epigenetic," with the latter representing heritable changes caused by mechanisms other than alterations in underlying DNA and being "modifiable," he explains. "Only about 10% of diabetes can so far be explained by genetics, for example," he notes.

And one factor he believes may be playing an important role in India is vegetarianism. People there consume high amounts of folate but are deficient in vitamin B12, creating a low-B12/high-folate intrauterine environment that "produces babies who are mostly insulin resistant." He is testing his hypothesis in the Pune Intervention trial, which began a year ago and involves giving adolescent boys and girls in the Indian region B12 supplementation. The participants and their offspring will be followed long term.

Maskarinec is skeptical of this theory, noting that most ethnic groups around the world are not B12 deficient. The Japanese Americans she is studying, for example, have very high per-capita meat consumption, she says.

The main message, she stressed, is that doctors need to understand that individuals of Asian descent and other ethnicities can have particularly high disease risks—not just for diabetes, but for breast and other cancers—at relatively low BMI levels.

"Just because they don't look fat doesn't mean they are healthy," she warns.

Maskarinec and Yajnick have disclosed no relevant financial relationships.

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