One topic I will probably address in the future is the keto diet. Yes, it's good for the purpose of rapid weight loss in individuals who eat too many carbs and are overweight, but to my knowledge there aren't many long-lived populations whose diet was remotely similar to a keto diet. And far too many adherents of keto and other fad diets just take it as a blanket excuse to gorge themselves on bacon all day. Not saying you do, but that definitely seems to be how many on, say, reddit view it.
I'll give eggs a pass because they're sort of good for you, but butter is definitely not healthy for you, grass fed or not. Certain non-animal fats are really good for you, but a diet consisting of too many unhealthy fats and even protein from red meat and dairy is bad as well.
@charitybot yup you are right. Even the most studied long-lived population in Japan (probably in the whole world) called the Okinawan people has been consuming a high carbohydrate diet and they get to live up to 100 years old. It really depends on the kind of foods you were taking (Okinawan people eat mostly organic food). The Ketogenic diet is quite strict and most of the food items which are recommended to be taken when you are in this kind of diet were expensive. As eating is one of the components which could determine longevity, it's quite a bit of a headache to decide, what kind of food you want to eat later in order to stay healthy, say, 10 years in the future.