When I hear doctors, trainers, and YouTubers talk about the benefits of a keto diet, I wonder if they ever think about the obvious downside to a high fat diet: the calories.
I don't subscribe to low-fat dogma that says that we should eat <10% of our calories from fat and that "fat makes us fat." That went too far. It went so far that people starting eating fat-free chips and cookies. "Fat" is an unfortunate homograph in the English language. I wish we would call dietary fat "lipids" but I also think the opposite of exceed should be subseed.
Anyway, fat does not make you fat. Overeating makes you too fat regardless of the source of the calories.
But one thing the low-fat and vegan advocates got right is that raising the caloric density of your diet makes it easier to gain weight, and that's what clinical trials repeatedly show. This makes sense. If you eat high-fat foods (cheese, ranch dressing, mayo, cream, etc.) you're eating more calories per volume, and it becomes super easy to overeat.
To give you an example, I weighed a pint of Ben & Jerry's ice cream (a concoction of fat and sugar, but 40% fat) before and after taking one bite with my spoon.
One scoop was 20 grams, or about 55 calories. Think about that, one bite is 55 calories. Think about that the next time you eat ice cream!
Adding even modest amounts of cheese and mayo (or oil) to anything will drastically increase the calories in the meal, and you won't necessarily feel fuller.
The one advantage of a high-fat diet is that it removes a lot of convenient food from your diet, which is primarily why people lose weight on such a diet. When you have to prepare everything and you can't grab something and go, then it makes it really hard and inconvenient to lose weight.
But don't full yourself by eating several ounces of cheese and tablespoon after tablespoon of mayonnaise that you're going to lose weight doing that. You won't.
My recommendation is the same: generous servings of starch (potatoes, rice), modest amounts of animal protein (chicken, beef, Greek yogurt), and some fruits and vegetables for vitamins and minerals.
Most people won't go wrong on such a diet, and in the absence of nutritionists, marketers, and trainers telling them what to eat, this is what most people (around the world) gravitate towards.