The point is, a high-fat diet isn’t natural for rats. I looked it up, and rats are listed as omnivores who will eat pretty much whatever is available, but prefer cereal grains. (They probably like looking at that American Heart Association seal of approval on the box.) When you feed an animal – or a human – an unnatural diet, you’re going to get negative results.
The Lipid Hypothesis became accepted partly because when researchers fed rabbits lard and cholesterol, the rabbits rapidly developed heart disease. Well, go figure … rabbits rarely attack pigs and eat them. When other researchers tried the same experiment on dogs, they couldn’t induce heart disease, no matter how much lard they fed them. So they concluded that dogs don’t get heart disease. But they do – if you feed them grains.
If rats eat a lot of fat and then become lethargic and stupid, that says nothing about how a high-fat diet affects humans. We’ve been eating fatty diets for hundreds of thousands of years. We didn’t become fat until we started eating grains. (And we didn’t become stupid until we started feeding fat to rats and thinking the results mean anything.)
In another rat study that hit the news this week, researchers suggested that high-fat, high-protein diet leads to insulin resistance. Once again, we’re looking at animals that aren’t eating anything close to their natural diet. If a high-fat, high-protein diet had the same effect on humans, the Inuits and the buffalo-hunting tribes should’ve been plagued by diabetes. They weren’t. But after Native Americans were herded onto reservations and forced to live on flour and sugar, they became one of the most diabetic populations on the planet – more than 50% in some tribes.