Several long term trends show that Americans, especially children, drink far less milk than they once did. And studies show that if they have consumed dairy it's probably a low fat or skim variety. Replacing whole dairy with low fat or fat free products removes much or all of the milk fat, along fat-soluble vitamins and minerals, typically bound in colloids (a type of nutritional matrix, another active research topic.) Children who do consume full fat dairy tend to be more metabolically healthy than those who do not, but more research would be great.

The problem with SAD (standard American diet) is extremely high refined foods with highly refined carbs(UPFs), and so often low vegetable, and they tend to really focus on lean muscle.

People often think animal fat contains toxins. That's generally false. Animal fat does contain multiple(likely all) fat soluble nutrients though, which are all core essential nutrients.

Most importantly, many don't eat the rest of the animal. Like the offal/organs or the bone/marrow or the collagen or blood ... These all are great sources of nutrients that lean meat and plants do not contain. Very critical to this understanding are vitamin forms. Animal sources of vitamins are generally more bio-available and potent, and then they're delivered in a rich nutritional matrix with other highly potent and bioavailable vitamins so you're getting a naturally balanced source of extremely good and vital nutritients. Sure, a carrot contains beta carotene which is vitamin a just like retinol is but retinol is much more potent version of the vitamin. And this is true for every single vitamin out there, and plants pretty much universally contain inferior(less potent, less efficacious) versions. Just like plant proteins are far less digestible than animal, often requiring double the amount per meal (around 20g vs 40g.)

But sure, like the article mentions. Calorie reduction goes hand in hand with protein reduction,, especially if you're eating excessive protein.