Humans have a particularly robust digestive system, compared to other animals; for instance, we can eat lemons. We could be regarded as highly omnivorous, and extreme generalists. This makes it difficult to model human dietary nature, because many animals can't handle a diet as varied as ours.
As far as mammals go, humans might actually be the most tolerant of a varied diet. This probably stems back to our early days, where scavenging was common. It's pretty apparent that at some point humans underwent intense selective pressure for dietary tolerance. I can't think of another mammal that can regularly eat things as diverse as corn, lemons, and beef, and not die. This makes it really difficult to find a good organism for modeling human dietary behavior. Even our close relatives, like Chimpanzees, would have issues when fed a normal human diet.
The issue here is the press. These little studies show a very narrow and tightly controlled (with rare exception) effect, and if you read these papers, the effect is usually very small or only for certain age ranges of mice. However, when the press release comes out, these caveats are totally ignored or buried at the end of the press article that the univ releases. This is usually accompanied by very pretty pictures of the PI that never touched the bench in a lab coat that has the name of a lab tech stitched onto it. That then gets spun around to a local news outlet that may or may not tell you about the limits of the study. If you are 'lucky' then you have a major news outlet pick it up and just copy/paste most of it and leave even more out. Then the blogs get a hand on it and somehow your buddies that made the original study are being accused of being lizard people working for the moon god Tsath-Satha. All along the way it gets distorted and the general public is rightfully confused.
Honestly, the blame lies with the researchers. We are where the 'buck stops'. That we allow the press to say these things and distort the work so much harms us and makes us less trustworthy the public that we are working to help. How to stop this is something that we could use help with.