Low-fat diets are healthy.
In young people, the often recommended low-fat, high-carbohydrate diet, usually works well. However, over a lifetime, in modern societies, that seems to change, and people become carbohydrate intolerant. Your hormones work against you, and you begin to get fat.
For most older people, it's been demonstrated that the "recommended diet" has no health benefits.
Worse than that, because it's making us fatter,the "recommended diet" is probably making us sicker.
Vegetarian Diets are the Healthiest.
Vegetarian diets are very hard to maintain. Vegetarians usually lack the fat-soluble vitamins, A, D,E, and K.
Saturated Fats are BAD.
Saturated fats are supposed to make people fat and clog the arteries. That's untrue. In the absence of insulin, saturated fats become the main fuel for your body.
In the presence of insulin, fats are broken down into fatty acids, and they should be stored in the adipose tissues within the body. However, as soon as that begins to happen, the hormone leptin in released which signals the appestat to stop you eating. (You should NOT get fat.) That mechanism fails if there is too much glucose in the blood. Insulin over-rides the leptin signal in order to burn or store more glucose.
The Framingham Heart Study dismissed diet as a cause of heart disease in the 1980s.
There is no relationship between diet and Cardiovascular Heart disease.
There is no relationship between dietary saturated fat and heart disease.
Vegetable Oils are better than Butter.
Not so. Vegetable oils are less stable, usually mono-unsaturated, or poly-unsaturated, rather than saturated fats, and they may create undesirable by-products when heated.
To make them stable for baking and frying, or for margarine, vegetable oils are hydrogenated, to change their chemical structure. Once thought to be safe, and cholesterol lowering, they are now considered dangerous, by many researchers.
Hydrogenated oils are known to produce great numbers of artificial chemical byproducts when heated. Nobody has been able to test but a few of these. Some are certainly carcinogenic.
Thirty years ago hydrogenated oils were everywhere. Your fish and chips were cooked in them. All baked products from commercial kitchens contained them. They were heavily promoted and thought to be "healthy."
Because the bad health effects of hydrogenated vegetable oils are now better known, their use has declined.
Today your food is probably cooked in palm kernel oil, or palm oil. From a health point of view, that might be good. These oils have a high smoke point, and because they have a lot of saturated fat, they will be much more stable than many other vegetable oils.
I don't know about costs, but we used to cook in lard, dripping and butter or even ghee. We could do that more.