It is partly a problem, but a big part is the demonization of animal fats in the west, especially cholesterol. Our bodies use cholesterol to synthesize testosterone. Low intake of cholesterol=low testosterone. Vitamin D is also necessary, and most men in west are deficient.
I wonder if they controlled for store-bought food vs meat-fed. First thing that comes to mind is that most dogs are fed processed, mostly vegetable-based food these days.
There are probably multiple interacting factors - but while we're all piling on with pet theories, here's one I don't see mentioned enough: simple lack of exercise (and sunlight). Globally, people are more sedentary than ever. Exercise boosts testosterone.
