Remember the good old days, when fat was the food villain? Or coffee (good in small quantities, though), carbs (the South Beach food imposter diet), salt, pickled foods, aged cheese? And let's not forget tuna, pork, beef (for a multitude of problems), chicken, eggs, any nonfarm-raised fish? Anything with preservatives? And then there was the spinach scare.
And, of course, there's high fructose corn syrup, responsible for the backlash of soft drinks touting their throwback to the very special...real sugar, which was the evil white powder of the 1970s which returned for a repeat performance in the late 1990s. And the artificial sweeteners: cyclamates, saccharine, aspartame. There's the reverse chirality sugar now that wreaks havoc on some digestive systems. And on the good side is stevia.
Now it's gluten, a protein found in wheat and some other grains, that many people are allergic to. Carbs, the staple of my diet during my avid cycling days, cause weight gain. What? No more bagels and pasta?
In my opinion, the concurrent problems of obesity and malnutrition are: processed foods, soft drinks, and the computer replacing active playtime (adult and children).