A gene variant much more common among Samoans than others, is thought to partly explain high levels of obesity among people from Samoa.

A gene found among nearly half of Samoans is thought to partly explain why the islands' population has among the world's highest levels of obesity.

Researchers emphasised the gene variant - which is much less common elsewhere – is not a dominant factor in people becoming overweight.

"Don't take this as 'You are Samoan, you are fated to be obese'," study author Stephen McGarvey, of Brown University in the US, said on Tuesday.

"We don't think that's true. We don't have any evidence that that's the case. A healthy diet and physical activity are still key to maintaining a healthy weight."



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While the variant tipped the balance toward excess fat storage, people with the variant were also less likely to have developed type 2 diabetes. Samoans have among the world's highest rates of the condition.

The findings hinted at an evolutionary story but more evidence was needed, McGarvey said.

"The earliest Samoans may have faced considerable food insecurity when sailing to and settling the South Pacific islands. Those who had this gene variant might have been more efficiently able to extract and store energy from the available food," McGarvey said.

"This may have led to natural selection favouring those who carried this thrifty gene variant, and could account for the notable frequency of the variant in contemporary Samoans."

The variant is virtually non-existent in European and African populations and is present at "very low" frequency among East Asians.

In samples of more than 5000 people from the Samoan islands studied since the 1990s, 7 per cent had two copies of the mutation and another 38 per cent had one copy. The other 55 per cent of Samoans in the study did not have the variant.

Those with the variant were more likely to have a higher body-mass index (BMI) than those who didn't have it.

The single genetic variant involved is associated with about 35 per cent higher odds of being obese compared to not having it.

While that elevated risk was much greater than any other known common BMI risk variant, overall it explained only about 2 per cent of the variation in BMI among Samoans, McGarvey said.

Researchers found fat cells exposed to the mutation stored more fats and did so more efficiently, using less energy.

While the variant helped explain why 80 per cent of Samoan men and 91 per cent of Samoan women were overweight or obese in 2010, it was just one of many reasons, McGarvey said.

"Samoans weren't obese 200 years ago. The gene hasn't changed that rapidly – it's the nutritional environment that changed that rapidly."

Commenting on the study, Auckland University professor of cell signalling Peter Shepherd said the findings probably meant that when people with the variant ate food, they would deposit more of it as fat tissue than people who did not have that version of the gene.

"Further research will be required to confirm this and we also need to understand how common this gene is in other Polynesian communities in New Zealand," he said.

"The finding that Samoan people have a higher incidence of this gene variant than Europeans shows that different groups in our society are facing different challenges in their efforts to reduce the impact of the modern environment," Shepherd said.

"This knowledge is important as it means we now need to think of strategies that take these differences into account, and to develop targeted strategies rather than trying to use a one size fits all strategy to tackle the epidemic of obesity and diabetes that is facing our society."

Dr Mike King, lecturer at the Otago University Bioethics Centre, said extreme care needed to be taken to avoid miscommunication or misinterpretation of the research findings.

"Obesity is a phenotype that is generally socially disfavoured, and this research risks creating or strengthening in the minds of others an association between Samoan people and obesity, and therefore promoting or supporting social disfavour and harmful discrimination," he said.

"The role of environmental factors not only on the claimed function of this gene variant, but also on the occurrence of obesity should always be explained in research of this type. These environmental factors can be cultural, social, economic, and political.

"They are extremely important, and often influenced by the views and actions of the population in question, and others."

More research was needed to evaluate and confirm the findings of the study.