South Asians' fat collects on internal organs, study finds
Published Friday, July 29, 2011 7:10AM EDT
TORONTO - Some weight-conscious people say calories go right to their hips -- but new research indicates that for South Asians, fat cells can make a beeline for internal organs such as the liver.
The discovery provides some backing for the message that Canadians whose families originated in the Indian subcontinent should aim to burn off excess calories.
South Asians have more risk factors for heart disease, including Type 2 diabetes, low "good" cholesterol and more abdominal obesity, according to previous studies by McMaster University in Hamilton and the Population Health Research Institute.
This time, the team took a deeper look inside the body -- a different approach from their population studies of the past.
"We measured many more things, including performing a fat biopsy and a muscle biopsy, MRIs of the abdomen and the liver, and we did this much more intensive, invasive examination in fewer patients to try and understand the mechanisms," said Dr. Sonia Anand, a professor of medicine and epidemiology.
The comparative study, sponsored by the Heart and Stroke Foundation of Ontario, was published Thursday in the medical journal PLoS ONE. It involved 108 healthy South Asians and Caucasians with an average age in the mid-30s and similar body mass indexes.
The South Asians had parents or grandparents who came from India, Pakistan, Sri Lanka or Bangladesh.
Anand said when South Asians consume more calories than they're burning off with activity, they're "energy-positive" and it normally leads to fat accumulation.
"We observed in South Asians that they were unable to fill their subcutaneous fat storage sites as much as white Caucasians were," she explained.
"And it's almost like they're impaired in the ability to expand fat in places underneath the skin. And because of this impairment, the fat cells kind of overflow with fat, and send the fat internally within the abdomen around the organs within the abdomen, including the liver."
This is bad because once a fatty liver develops, blood glucose increases, good cholesterol goes down and bad cholesterol rises, Anand indicated.
"So this study has kind of added to our understanding -- missing pieces of the puzzle as to why South Asians develop these risk factors, and why they're so different from white Caucasians."
She said Type 2 diabetes is at epidemic proportions in India and among the one million-plus South Asians who live in Canada.
"So it's really important that we understand why this occurs in order to try and prevent it," Anand said.
"What we observed when we look under the microscope at the fat biopsies is that South Asians have larger fat cells, and they are basically stuffed full of fat, whereas the white Caucasians are able to increase the number of fat cells they have -- so they're not very wide or large fat cells, they just increase in number."
Dr. Gurdeep Parhar of the University of British Columbia's faculty of medicine said the study is "exciting" because it actually points to an underlying cause for the higher risk of cardiovascular disease among South Asians.
"A lot of times before, we were looking at whether it was diet, lifestyle, genetic, and this is coming closer to identifying a more concrete explanation for what's going on," he said from Vancouver, where his practice includes a large immigrant population, including many South Asians.
Parhar said the findings help explain weight around the abdomens of South Asians who have slender arms and legs.
"I can't tell you the number of times I've had liver abnormalities seen on blood work and then I do ultrasound and find a fatty liver. And thinking back on it now, the ratios must be about 20 to one for South Asians to my white patients in terms of how many of them have fatty livers."
He described the cell differences that were identified as "a bit ominous" and "a bit of a wake-up call for some of us."
Parhar, whose family came to Canada from India, said it's unfortunate the study didn't identify whether the South Asians were relatively new arrivals, or their families had been here for a few decades.
"I've been in Canada since I was a year old -- I'm 42 now -- so basically I've grown up here. So am I in the same category as somebody who's 42 and my body build, but they arrived five years ago? That would be an interesting distinction because that would also help to stratify which patient groups I'm more aggressive with."
Dr. Thomas Ransom, an endocrinologist in Halifax with a special interest in obesity, said the research further emphasizes considerations that doctors already take into account, such as waist measurement.
"People of South Asian descent, particularly, are deemed at higher risk at lower waist circumferences than their Caucasian counterparts," he said. "What this has done is sort of confirmed that, using the body mass index."
The study will hopefully raise awareness and change the threshold for intervening and screening for complications, he said.
"So that if someone of South Asian descent appears to be, 'only a little bit overweight,' we would actually say, 'But, you know what, you're at increased risk and I'll screen for diabetes and blood pressure and things like that."'
Anand, who was walking and talking on a cellphone as she was interviewed, said there is a lot that people of South Asian origin can do to deal with weight issues.
"What they can do is prevent themselves from, at the end of the day, being energy-positive, which means not consuming as many calories. Or if they do consume substantial calories, they burn it off through physical activity, so basically prevention of weight gain. Or in individuals who already have abdominal obesity, trying to lose weight."