What I don't understand, is why when atherosclerotic studies are performed on other animals (mice, rats, monkeys) would they use a high fat/cholesterol diet to induce atherosclerosis? If high cholesterol and fat is good for our species, what does it prove by inducing it in other animals?
The short answer is "nothing."
Nutritional science (what studies get funded, which get published, which get promoted) is highly flawed, and it is also highly influenced by ideological commitments. It is almost entirely based on either epidemiology, the weakest form of evidence, or else animal studies like the ones you mention, which cannot be extrapolated to human beings because of our very different diets, physiologies, and digestive systems.
To be fair, conducting long-term, randomized controlled studies of nutrition on humans is difficult or impossible from an ethical, pragmatic, or financial perspective. That's just a scientific limitation, though, which could be made clear in the reporting, although it never is. It's not the main problem.
The main problem is that financial interests and ideological commitments dictate much of what happens in this field. The financial interests are pretty obvious. Billions of dollars are at stake in the "cholesterol is bad" story. Think of all the low-fat, low-cholesterol products that have been sold, and all the money made by pharmaceutical companies selling cholesterol-lowering drugs. These are often the companies funding the research. Do you think their interests influence which studies get done, which get published, and which get promoted? Of course.
The ideological commitments are a little harder to see. The anti-saturated fat narrative, for instance, is linked in its origin not just to crap science -- I assume we all know the story of Ancel Keys* -- but to the Seventh Day Adventist Church, which is anti-meat, and whose universities still fund much of this research. The ideological influence continues to be widespread and can be seen in the WHO's decision-making, for instance (one reason why their apparent complicity in covering up the virus outbreak in China did not surprise me); their committee is largely vegan and vegetarian (meat is bad, so saturated fat must be bad), although they don't declare their biases. These people often have an emotional commitment to their beliefs that resembles a religion.
In addition, these researchers, board members, journal editors, etc., have often spent their entire careers believing in and doing work to support the "saturated fat is bad" narrative. So they do not want to look at conflicting evidence that suggests all their work has been for naught -- or worse, has misled and harmed people.
I don't want to go on too long about it (too late, you say). Basically, nutritional science is characterized by reliance on the weakest forms of evidence and is driven by ideological commitments and financial interests.
*Somewhere in a dingy basement, they recently found an unpublished research study by Keys that was impressively well-controlled and which completely disconfirmed the saturated fat hypothesis. He buried the study, did not submit it for publication.
