Fruit flies that grow obese after eating a diet loaded with fat could lead the way to the core elements of obesity, say scientists.
The demonstration that flies do become obese on a high-fat diet (HFD), much as humans do, indicates that the ability to become obese goes way, way back, researchers said.
It is harder to survive in times of scarcity. As a result, organisms may be poised to maximize their food intake. At the other extreme, this can lead to obesity. It may be that the propensity has always been there," said Sean Oldham of the Sanford-Burnham Medical Research Institute.
In the new study, the team fed flies a HFD consisting of 30 percent fat in the form of coconut oil. And the flies got fat.
Flies can only grow so big because they have a rigid exoskeleton, the researchers said.
The obese flies also showed many of the familiar signs of obesity; they developed high triglycerides and disruptions in the balance between insulin and blood sugar, along with heart dysfunctions reminiscent of diabetic cardiomyopathies.
Detailed studies of heart function in the flies revealed an increase in cardiac lipids, reduced cardiac contractility, blockages, and structural pathologies.
"Whether this directly relates to what we see in humans, we don't know. As in diabetic cardiomyopathy, the fly hearts become less efficient," said Bodmer.
Treatments that reduced the insulin-TOR activity prevented the accumulation of excess fat in the insects and protected their heart.
"When we manipulate this pathway in the hearts of flies, they are still obese, but their heart is 'blind' to the systemic effects," said Bodmer.
The finding suggested that treatments designed to alter insulin-TOR signalling in specific tissues might hold promise.
The findings were published in Cell Metabolism.