Studies and news reports keep coming about how sleep loss / sleep deprivation is associated with obesity and type 2 diabetes - but the studies are far from conclusive. One problem is that it is difficult to control diet and sleep behavior in humans over a long period of time. Animal studies may help us understand the link between sleep and obesity, since animals can be controlled in the lab. Animal studies in the past have shown links between sleep loss and metabolic changes, but this is usually weight loss and could be due the stress of forced wake time.
Vetrivelan et al have performed an interesting study on rats published in this month's Sleep Journal. They produced brain lesions in the hypothalamic regions of rats as an animal model for chronic, partial sleep loss, and they followed the rats for 2 months (relatively long time for a rat).
Results showed that on average, the brain lesions resulted in 40% reduced sleep compared to normal rats - equivalent to reducing sleep from 8 hours to 4.8 hours per night in humans. However, the rats with brain lesions did not become obese or develop metabolic syndrome. In fact, there was a decrease in blood glucose, cholesterol, and triglycerides!
The authors are not sure why there is a different response in rats and humans to sleep deprivation. When humans voluntarily go without sleep, their food intake increases and are less active. However, the rats in this study did not consume more food and were more active than control rats. The authors concluded that chronic sleep loss per se does not lead to obesity or the metabolic syndrome, at least in rats.