That's begun to change. I anecdotally know a lot of people on a high-fat diet (Keto and such) and it has really worked for them. Inflammation is way down, energy is way up, weight is down, blood pressure is down, cholesterol is down, etc.
Sugars / refined starches seem to be the nutrition villains, not natural, saturated fats. (But who knows! The recommendations change almost daily, it seems.)
Anecdotally I too am moving towards LCHF/Keto and so far my health has improved drastically from primarily focusing on adding fats back in after years of carefully measured low-fat low-calorie diets did nothing for me.
Anybody who has done keto and lost weight certainly does not say they had evergy on it. Those first couple weeks are terrible and you never quite have the energy you want. Thankfully it is a short term diet with specific targets in mind. Any positive effects after stopping keto are from the weight loss in general. Even keto diets recommend against a high saturated fat content but with keto your body is in a specific state that blunts the effects of a high saturated fat intake.
When you go off keto you cannot maintain the high saturated fat intake without measurable negative impacts.
Who says it? I had more energy on keto, except for one day (around a week after starting) that felt terrible and was fixed by drinking water with salt and potassium. Keto diets don't recommend against a high saturated fat content, only some do because of the common misconception that it is bad. There are no studies showing bad effects of saturated fat by itself. It's the carbs what causes the problem, fat only makes it worse.
In the anecdotal cases I mentioned, inflammation is a catch-all. More specifically, congestion and joint pain decreased significantly. In one case, I know someone who had many days where she wasn't able to walk due to joint pain. Those days appear to be gone.
The article i posted specially attacks this. Inflammation is a symptom of many things including cancer, but isn't something you really aim to treat. And there is no good evidence that there is such a thing as an anti inflammatory diet.
Sugars / refined starches seem to be the nutrition villains, not natural, saturated fats. (But who knows! The recommendations change almost daily, it seems.)