A virus that may encourage the body to grow more fat cells could, paradoxically, lower diabetes risk.
Nikhil Dhurandhar at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, and colleagues examined the long-term effects of a common virus ? adenovirus-36 (Ad-36) ? on humans.
The team analysed blood samples made available from 1400 volunteers in a decades-long epidemiological study. The researchers detected antibodies to Ad-36 in 14.5 per cent of the subjects when they first joined the study ? a prevalence in line with studies on the US adult population.
Ten years later, those individuals naturally infected with Ad-36 had a higher body mass index and body fat percentage than those who were not infected ? but their blood sugar and insulin levels were healthier.
Fat 'depots'
Animal and cell studies offer an explanation, says Dhurandhar. They suggest that Ad-36 increases the number and size of fat cells, or adipocytes, providing additional "depots" for any fat coming from excessive calorie consumption.
Under normal circumstances, the number of these fat storage cells stays constant in adulthood, no matter what dietary choices people make. The extra cells from Ad-36 may make the body more likely to store excess fat, but that means less fat is left to travel to other areas, like the liver, where it can have toxic effects. The adipocytes may also store more sugar, helping to keep blood sugar levels under control and maintaining insulin sensitivity to glucose.
"That is where the apparent paradox is not really a paradox," says Nicola Abate, an endocrinologist at the University of Texas Medical Branch at Galveston, who was not involved in the study.
Abate says the findings underscore the need to separate weight from metabolic disease: "It's not how much fat a person has that determines the health complications, it's the function of adipose tissue."
Safer treatments
The phenomenon isn't unique to Ad-36. Abate and Dhurandhar note that a drug called Pioglitazone, once widely used to treat type 2 diabetes, improves insulin sensitivity but also causes those taking it to gain weight. The drug has now fallen out of favour because it triggers a number of unwanted negative side effects; it is associated with a greater risk of bladder cancer, for example.
Dhurandhar thinks Ad-36 may ultimately lead to a safer and more efficacious therapy than Pioglitazone. He is developing a drug to harness the properties of the virus.
US obesity and diabetes rates are projected to top 60 and 30 per cent, respectively, by 2030 ? but there has been little population-wide success with weight loss programmes. "Can we bypass the whole issue about your weight loss and can we still give you metabolic benefits?" asks Dhurandhar. "In theory, at least, it may be possible."
Dhurandhar and his team presented the work at the Obesity Society meeting in San Antonio, Texas, last month.
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