There is little debate that obesity presents a public health issue in North America -- obesity rates have more than doubled over a generation in the United States, according to the Centers for Disease Control and Prevention. But the causes of obesity -- and therefore, the solutions -- are not as obvious, according to research presented this week at a media workshop run by the Canadian Institutes of Health Research.

The problem of obesity cannot be reduced simply to genetics, the researchers said, and it also cannot be blamed solely on our environments or learned behaviors. Media coverage, they advised, should highlight that the obesity epidemic is the result of a variety of factors, and that change requires a comprehensive approach that tackles the problem from all sides.

"Obesity's not rocket science," said Dr. Diane Finegood, director of CIHR's Institute for Nutrition, Metabolism and Diabetes. "It's a lot more complex."

Biological factors like genetics or diet play a key role. Genetics help to determine where we gain weight, said Dr. Jean-Pierre Despres, a professor at Universite Laval in Quebec. And where our genes tell our body to store fat -- whether we're an apple shape that stores it on our stomachs or a pear shape that stores it on our hips -- is an important factor for determining our cardiovascular risk, he said. Research done by Despres and others has shown that excess fat around the stomach -- visceral fat -- carries a higher risk for both diabetes and cardiovascular disease, no matter what a person's body mass index is; as a result, Despres advocates for the importance of waist circumference as a vital health measurement to be used in conjunction with more traditional indicators of cardiovascular risk like blood pressure and blood cholesterol measurement.

Despres described an international study he was involved with, where 6400 doctors in 63 countries were shown how to properly measure waist circumference in their patients. In looking at the waist measurements and health status of 170,000 patients, the researchers found higher rates of diabetes in those with the highest waist measurements, whether or not their body mass index classified them as overweight or obese. "This is really making the point that private care physicians, when they are told and shown how to measure waist circumference, are not measuring noise," he said.

For someone who discovers that his or her waist is too large, and wants to lose weight to reduce the measurement, the solution would seem to be easy: eat less and move more. "Obesity is the outcome of a positive energy balance," said Dr. Angelo Trembley, a professor at Universite Laval. But research done by Trembley and others has shown that it may not be that simple. A variety of biological factors that wouldn't automatically occur to us may also be contributing to the dramatic rise in obesity rates, he said.

There is evidence suggesting that micronutrients -- vitamins and minerals found in food -- may affect fat loss or gain, Trembley said. For example, a study led by Trembley found that female subjects in a placebo group couldn't achieve significant weight loss, despite following a carefully restricted diet, while those who took a calcium supplement showed better weight loss results. It's possible that as with glucose, the brain can recognize low levels of micronutrients like calcium, Trembley said, and regulates appetite control in order to correct them.

"We cannot exclude the possibility at this time that some individuals might gain some weight due to deficiencies in some vitamins and minerals," he said.

Poor sleep is another factor that may affect the body's ability to control appetite, Trembley said. A lack of sleep can increase ghrelin and decrease leptin, two hormones, which results in increased hunger and appetite. The Quebec Family Study showed that short-sleepers were more likely to be heavier, he said, with more body fat and a larger waist circumference.

"We are maybe not making optimal life choices," Trembley concluded. "Modernity is providing a new way of living that is providing a positive energy balance."

Data collected by Dr. Gillian Booth, and other researchers working with her at Toronto's St. Michael's Hospital, illustrated that it is not just our individual lifestyle choices that are contributing to obesity, but our environments, our cultures and our political landscapes as well.

North America is facing an epidemic of diabetes due to increases in obesity rates, Booth said, and her report on diabetes in Toronto for the Institute for Clinical Evaluative Sciences showed that diabetes rates in the city of Toronto were highest in areas of the city found to be less friendly to healthy choices -- fewer sidewalks and bike paths, less access to fresh fruits and vegetables, fewer parks and recreational spaces, and fewer family physicians taking new patients. Diabetes rates also showed strong correlations to ethnicity -- many non-white ethnic groups have higher diabetes rates than Caucasians -- and economics -- there were higher diabetes rates in areas with lower average incomes.

"It may be that the availability of resources and where you live may be much more important for socially disadvantaged groups," Booth said, "who are already at a higher risk for diabetes."

If we know that genetics play a role, and lifestyle plays a role, and environment plays a role, how do we fight the obesity epidemic? By attacking it from all sides, said Dr. Kim Raine, a researcher at the University of Alberta in Edmonton. We know that toxic environments that promote obesity don't occur suddenly but develop over time, Raine said, and that there needs to be social action at multiple levels in order to promote healthy weight loss. "We do have power in collective efforts."

For changes to make a difference in people's behavior, and then in their health, they must be comprehensive, addressing the physical, economic, sociocultural and political environment people live in, Raine said -- comparable to the public health campaign against tobacco use.

For example, research done at the University of Alberta found that the city of Edmonton had 61 supermarkets, but 761 fast food outlets, many of which were concentrated in poorer neighborhoods. There were 2.7 times the number of fast food restaurants in poorer neighborhoods than in middle-class or high-income neighborhoods, Raine said, and a similar ratio has been found in research done in the United States and Australia. A promotional campaign encouraging people to eat fresh fruits and vegetables will have a limited effect if people cannot easily find those items near their homes.

Effective interventions do not have to be excessively expensive, Raine pointed out. The Children's Lifestyle and School Performance Study, a project of Dalhousie University in Nova Scotia, found that children in schools with a nutrition program that included parents, teachers and their community -- at a cost of only $100 per child annually -- had obesity rates less than half those of children in schools without the program. But children in schools with a more basic nutrition program didn't show results much better than those in schools with no program at all. The difference illustrates why single moves like removing pop machines from schools are a good first step, she said, but not a total solution.

"It's the comprehensive nature of the intervention that seems to make the difference," Raine said, "not just little one-offs."