As someone who's struggled with his weight all his life (and who comes from a family with similar problems), I've long been fascinated with the science of weight and obesity; many years ago I listened to a Quirks & Quarks segment detailing the theory that the modern obesity epidemic was the result of a bird flu that affected our gut flora and changed our metabolisms to make us hungrier and more susceptible to convert the food we ate to fat.
I've not been able to locate that episode since, but the theory has lingered in my memory. This morning, I found this long excerpt from The Secret Life of Fat: The Science Behind the Body's Least Understood Organ and What It Means for You, Sylvia Tara's 2016 book about Nikhil Dhurandhar and Richard Atkinson's research at the University of Wisconsin, Madison on the role of viruses first found in poultry in causing obesity in humans and other animals.
I lost ~100lbs in 2002/3, simply by cutting out carbs — while maintaining a low-activity/high-calorie diet. I've kept most of it off since then (though over the years, I've had to increase my activity and reduce my calories as I got older). It's obvious to me that weight is not a simple matter of calories burned and calories eaten — some people gain weight more easily and others do not. Some people need to eat more than others to maintain their weight, irrespective of activity levels and their muscle-mass.
The introduction to Tara's book was sufficiently interesting to me that I've ordered the book. Significantly, it insists that weight is not a moral matter — not a matter of low willpower or other failings.
It turned out that Ad-36 had similar qualities to SMAM-1 in chickens. Atkinson thought Ad-36 might very well be a mutated form of SMAM-1. When Dhurandhar infected chickens with Ad-36, their fat increased and their cholesterol and triglycerides decreased, just as had happened with SMAM-1. Dhurandhar wanted to make sure he was not getting a false positive, so he injected another group of chickens with a virus called CELO to ensure that other viruses were not also producing fat in chickens. Additionally, he maintained a group of chickens who had not been injected with anything. When he compared the three groups, only the Ad-36 group became fatter. Dhurandhar then tried the experiments in mice and marmosets. In every case, Ad-36 made animals fatter. Marmosets gained about three times as much weight as the uninfected animals, their body fat increasing by almost 60 percent!
Now came the big question: would Ad-36 have any effect on humans? Dhurandhar and Atkinson tested over 500 human subjects to see if they had antibodies to the Ad-36 virus, indicating they had been infected with it at some point in their lives. His team found that 30 percent of subjects who were obese tested positive for Ad-36, but only 11 percent of nonobese individuals did—a 3 to 1 ratio. In addition, nonobese individuals who tested positive for Ad-36 were significantly heavier than those who had never been exposed to the virus. Once again, the virus was correlated with fat.
Next, Dhurandhar devised an even more stringent experiment. He tested pairs of twins for presence of Ad-36. He explains, "It turned out exactly the way we hypothesized—the Ad-36 positive co-twins were significantly fatter compared to their Ad-36 negative counterparts."
Of course, it's unethical to infect human subjects with viruses for research, so the study can't be perfectly confirmed. But, Dhurandhar says, "This is the closest you can come to showing the role of the virus in humans, short of infecting them."
The Mysterious Virus That Could Cause Obesity [Sylvia Tara/Wired]
(Image: Confused Chicken, Matt Davis, CC-BY)