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Overweight Because of Attitude or Altitude?


Scientists have recently learned that certain gene defects and high altitudes may be a factor in keeping certain people thin and free of diabetes. Mice bred with a missing gene that makes an enzyme called FIH, were less likely to gain weight, have fatty livers or develop diabetes, even when fed a high-fat diet.

FIH affects the body’s physiologic response to low oxygen levels, which occurs at higher altitudes. The mice took in 20 to 40% more air than normal, had faster heart rates, and drank 30 to 40% more than mice without the genetic mutation. All mice were also fed a very high fat diet (60% of calories). The FIH-deficient mice did not show any effects, while the normal mice gained weight, developed a fatty liver, and became resistant to insulin.

When the researchers at the University of California, San Diego analyzed the results, they discovered that the mouse was reacting as if it were at an altitude of 14,000 feet, about the height of Mount Rainier in Washington State, where there is about a 15% oxygen level. To compare, oxygen at sea level is about 22%.

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Study authors draw a link between the higher altitude of states such as Colorado and the improved insulin sensitivity of the populations in those states, however, the research may not be completely relatable to humans. The human body has the ability to adjust to altitude levels over time by adding more red blood cells to compensate for the lower oxygen levels. Mice do not adapt and instead compensate by expending a large amount of energy hyperventilating.

Genetic defects or mutations are known to be a factor in the propensity to develop obesity in humans, but some studies emphasize that people do not have to completely abandon all efforts at lifestyle changes to become healthier. After all, residents in Colorado, who only have about a 20% obesity rate according to CDC data, are about 11% more likely to be active than the majority of Americans in other states, according to data from the Kaiser Family Foundation.

In the April issue of Archives of Pediatrics & Adolescent Medicine, adolescents who were genetically predisposed to obesity were able to control body weight by increasing physical activity each day.
Jonatan R. Ruiz PhD of the Karolinska Institute in Sweden and colleagues studied 752 adolescents, more than half with one or two mutations of the FTO gene which is strongly associated with body fat. Each copy of the mutation is associated with about a 3.3 pound weight increase over those with normal genes.

Among the participants who meet the daily physical activity recommendations of 60 minutes a day, the effect of the genetic mutation was much lower than those who exercised less. Body mass index (BMI) of those with the defect who did not meet the recommendations was 0.65 more than those who were normal, while those who exercised were only 0.17 higher.

“There is compelling evidence that human obesity is a multifactorial disorder where both genes and lifestyle factors, including diet and physical activity, are important contributors," the authors write as background information in the article."