Mice fed a high-fat diet rich in corn oil developed lethargy and pre-diabetic symptoms in less than two months, while mice eating olive oil remained active and healthy, according to a new study from the University of British Columbia.

The group that was fed corn oil developed insulin resistance and impaired glucose disposal and showed reduced physical activity compared with mice on the olive oil diet and a low-fat control group, according to biologist Sanjoy Ghosh.

“We found that glucose disposal was delayed in corn oil fed mice compared to olive oil fed mice, which essentially means that corn oil fed mice became pre-diabetic within six weeks,” Ghosh said in an email interview.

The mice on the high-fat diets derived 40 per cent of their calories from oil. Most North Americans get 32 to 34 per cent of their calories from fat, but one in five exceeds 44 per cent.

This new research, published in the Journal of Nutritional Biochemistry, is the latest in a series of studies suggesting that widely used vegetable oils rich in Omega-6 polyunsaturated fatty acids may be injurious to health. High levels of Omega-6 — abundant in corn and cottonseed oil and to a lesser degree soybean oil — have been associated with cardiac and inflammatory disease in lab animals and metabolic illness in humans.

Other studies have shown that excess Omega-6 can induce depression in humans, which is also linked to reduced physical activity.

“Loss of physical activity and development of insulin resistance under a high-fat diet, as performed in this study, is well established in humans,” he said.

The chemical composition of fats in the Western diet has changed dramatically since the 1960s, as people replaced animal fats with vegetable-based fats.

Ghosh said that rising rates of human obesity and sedentary behaviour over the past 30 to 50 years mirror the rise in Omega-6 polyunsaturated fatty acids in our diet, which in excess interfere with the healthy effects of Omega-3 PUFA.

North Americans typically get seven per cent of their energy from Omega-6 PUFA, about seven times what is nutritionally required.

“Although various other detrimental effects of Omega-6 PUFA are known, this study is the first direct evidence linking an improper diet to physical inactivity,” said Ghosh.

rshore@vancouversun.com

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