Scientists have long believed that humans and animals have a natural disposition to select a balanced diet with all necessary nutrients and suitable for the respective environment.

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But the nation's soaring obesity rate offers evidence that in the animal kingdom, humans are flunking in their "nutritional wisdom."

Where nature fails to reduce weight, human ingenuity (and marketing) takes over, with a billion-dollar weight-loss industry advancing programs that entreat Americans to modify their habits and regain their "nutritional wisdom" and return to their "normal" and slimmer weight.

But returning to our natural state, nutritionwise, may not be so easy, and overweight Americans may be throwing their money away.

New study findings suggest that "nutritional wisdom" goes out the window when unhealthy food choices are more available than healthier nutrients.

Researchers performed tests with rats and found that those faced with extra fatty food alongside nutritional food gained more weight.

Researcher Michael Tordoff, from Monell Chemical Senses Center in Philadelphia, said the study in rats may point to a model for human obesity, in which the availability of the wrong food can override healthy physiological controls of food intake. His findings are published in the current issue of The American Journal of Physiology.

The recent focus on controlling obesity has been on physiological causes for the extra weight -- whether it be genetic makeup, hormonal differences, or neurotransmitters involved in ingestion and body weight.

But these findings suggest that this may be the wrong direction for addressing obesity. Availability of food, and not the physiological actions of the body, may be the culprit of "obesity by choice."