Actually there are a lot of explanations. Some of it is metabolic rate, some of it is just plain body type. Now there might be others but for the most part it actually pretty sensible.
As for the virus explanation. This one comes around every decade or so (Dennis Leary made fun of the virus explanation on his album that came out in 1997, not saying Leary know anything about weight loss, just saying this isn’t the first lap for the virus thing), so far nothing has actually come from it. You’d figure they’d at least find something to kill the virus.
“As for the virus explanation. This one comes around every decade or so”
That it came around in 1997 doesn’t equate to “every decade or so,” nor does the fact that it’s a previously noted association mean there’s nothing to it. On the other hand, this is the first time the method of action for producing obesity has been demonstrated. If someone can’t see the significance of finding that a commonly acquired virus DEMONSTRABLY prompts stem cells to convert to fat cells, I’m not sure there’s any point debating any further.
Additionally, once an individual has a significant increase in fat cells it’s going to be a problem for them almost regardless of how they’re currently eating. Weight gain is a self-promoting cycle beyond simply “food taste good, I want eat more food.”
Viruses are darned hard to kill if your body doesn't do it on its own. No cure for the common cold either.
Might be something good to come from all the money put into AIDS research. Well *some* of the money.
For most viral diseases, vaccination, which trains your body to kill the virus, is the answer rather than trying to kill it after you get a bad case of it.