TORONTO -- The body mass index (BMI) cutoffs used to determine obesity and diabetes risks are not appropriate for diagnosis and treatment of people of colour and could be putting their health at risk, a new study suggests.

The of 1.5 million people found that Black, Asian and other people with non-white ethnic backgrounds are more likely to develop Type 2 diabetes at a much lower BMI than white patients. And scientists said many patients of colour will 鈥渟lip through the net鈥� if doctors keep using broad guidelines which were set using white patients as a measuring stick.

鈥淢any [people of colour] will needlessly slip through the net, leaving them unknowingly at risk of Type 2 diabetes,鈥� Dr. Rishi Caleyachetty, the study鈥檚 lead author and epidemiologist at the University of Warwick in the U.K. .

The study, published in the journal Lancet Diabetes And Endocrinology, called for new ethnic-specific BMI cutoff points. But if that doesn鈥檛 happen, she and others would be extremely concerned.

鈥淎 blanket approach is not acceptable any longer,鈥� added co-author Dr. Paramjit Gill, professor of general practice and head of the division of health sciences at the University of Warwick said in the release. 鈥淭his work highlights that we need evidence for all ethnic groups as they are at risk of diabetes at different levels of BMI.鈥�

A person鈥檚 BMI is calculated by analyzing their height and weight. Right now in the U.K. and Canada, if a person鈥檚 BMI is 30 Kg m-2 or more they鈥檙e considered obese; and doctors then typically take precautions to prevent them from developing Type 2 diabetes. But that threshold is too broad, the researchers say.

When compared to white patients of a similar age and gender, the study found the BMI cutoffs were much lower when determining diabetes risk for people of colour:

  • for South Asians: 23.9;
  • Chinese: 27;
  • Black: 28.2; and
  • Arab: 26.8.

This means that if doctors want to more accurately assess a person鈥檚 risk of Type 2 diabetes, they should be taking into account people鈥檚 ethnic backgrounds.

Canadian experts have had similar concerns about BMI limitations for years.

鈥淭his is not a surprise,鈥� Canadian obesity specialist Dr. Sean Wharton told CTVNews.ca in a phone interview. 鈥淭hey were designed primarily for white males and did not speak to the South Asian female, African American female or many other ethnic groups.鈥�

Wharton, the medical director of a clinic specializing in weight and diabetes management in Burlington, Ont., explained that differences in BMI cutoffs are based on slight variations in how people with different ethnic backgrounds store excess energy in their body.

He said the study confirms that BMI values shouldn鈥檛 be used to determine if someone is obese or assess their actual health risks. And Wharton and his colleagues were critical of doctors and public health bodies using BMIs when deciding health interventions, something he noted in recommendations published in the .

鈥淲e should not use BMI. We should use the specific health-related matters, such as their blood pressure or their blood sugar,鈥� he said, adding that he was frustrated that countries don鈥檛 take into account ethnic diversity in patients because it has meant differences in health outcomes, like an increased risk of Type 2 diabetes.

鈥淐anada is a diverse population and we should treat it as such鈥�