During adulthood, our bodies tightly regulate the number of fat cells, which could explain why it seems easy to gain back lost weight.
Doctors have found more evidence that a viral infection can trigger obesity. And no, the virus doesn't live on cheese puffs and Twinkies.
Researchers at the University of California, San Diego, found traces of adenovirus 36 (AD36) in an alarming number of obese children and went so far as to claim that there is a positive association between the presence of the virus and obesity, as reported this week in the journal Pediatrics.
Excess calories and inactivity are clearly associated with obesity. And yet some children who have junk-food-filled diets and an exercise routine comprising entirely of walking back and forth from the refrigerator and sofa do manage to remain relatively thin. Why?
In my blood
Genetics, a popular rationale for all that's right or wrong with any given person, can't explain all cases of obesity, doctors say, particularly the sharp rise in childhood obesity. Bad habits among children have remained constant over the last two decades, but the child obesity rate has nearly tripled during this time.
AD36 is one of dozens of adenoviruses that are common causes of respiratory infections. Studies dating back to the 1990s have shown that lab animals deliberately infected with this human virus can get fat. In recent years, other studies have shown that upwards of 30 percent of obese adults have been infected by AD36, compared with only 10 percent of normal-weight individuals. The theory is that the virus targets immature fat cells and gets them to mature and proliferate rapidly.
This latest UC San Diego study, led by Jeffrey Schwimmer, examined 124 children; slightly over half were obese. Among all the children, only 19 (or about 22 percent) had been infected with AD36, a fact determined by the presence of AD36-speciﬁc antibodies in their blood. But among these infected kids, nearly 80 percent were obese.
More surprising to Schwimmer's team, the infected obese children were much heavier than the non-infected obese children. The average BMI of the obese kids was about 33; but among the infected obese kids, the average BMI was over 36.
This translates to an average, extra bulk of 35.5 pounds (16 kilograms) for those with the AD36 virus antibodies. That's a huge amount of extra weight for adults, let alone kids. Sadly, most obese kids will be obese adults and have a lifespan shortened by up to 20 years. A study out this year suggested obese men could die eight years earlier than other men.
Clearly you don't need a virus to get fat; bad food and eight hours of daily TV-watching can work well for you in that regard. But as skeptical as you (and I) might remain, some doctors are becoming increasingly convinced that AD36 is playing some role in the obesity epidemic. Schwimmer's team indeed has upped the ante by finding that those once infected have a high probability of being even heavier than other obese individuals.
What Schwimmer and others haven't been able to establish, though, is cause and effect. Is AD36 a cause of the weight gain, or is the infection the result of having certain kinds of fat cells that the virus happens to like? Or, are obese people predisposed to persistent AD36-speciﬁc antibodies after infection? That is, maybe most people have been infected, but obese people maintain the presence of antibodies longer.
So many unknowns. Makes you want to do something crazy like eat better and exercise, just in case.