http://www.health.harvard.edu/heart-health/the-truth-about-dietary-fat
For years, low-fat diets were recommended as the antidote to high cholesterol and heart disease. But that strategy didn't work, and it may have helped fuel the twin epidemics of obesity and diabetes by encouraging people to replace healthy fats with sugar and refined carbohydrates. Current dietary guidelines give considerable leeway in dietary fat, recommending that you get 20% to 35% of your daily calories from fat. Even more may be fine, as long as it's mostly healthy fats from fish and plant sources, such as avocados, nuts, and vegetable oils. These are considered good for the heart because they tend to lower total and LDL cholesterol and may even be associated with reduced levels of chronic, low-grade inflammation — the kind that fuels heart disease.
For years, experts recommended low-fat diets as a way to lower cholesterol and heart disease risk. Today, we know that low-fat isn't the way to go after all. A healthy diet includes plenty of "good-for-you" fats — and limits the unhealthy ones. Current dietary guidelines recommend that you get 20% to 35% of your daily calories from fat. Even more may be fine, if you follow these simple guidelines.
Favor the "good" fats
The best sources of healthy fats are oily, cold-water fish, such as salmon and tuna; plant sources such as avocados and nuts; and vegetable oils, such as olive, canola, soybean, and cottonseed oils. These fats promote heart health because they lower cholesterol levels — and they may even fight chronic inflammation, which may contribute to heart disease.
It's okay to get up to 35% of your daily calories from fat — as long as most of it comes from sources like these.
Limit saturated fats
Typical sources of saturated fat include animal products, such as red meat, whole-fat dairy products, and eggs, and also a few vegetable oils, such as palm oil, coconut oil, and cocoa butter.
Saturated fat can increase your levels of "bad" LDL cholesterol. But it has some benefits, too — it lowers triglycerides and nudges up levels of "good" HDL cholesterol.
The role of saturated fat in heart disease is currently under debate. For now, it's best to limit your intake of saturated-fat–rich foods.
Avoid trans fats
Trans fats are found in many commercial baked goods, processed foods, solid margarines, and deep-fried restaurant foods. These fats have no nutritional value — and we know for certain they are bad for heart health. Trans fats increase LDL cholesterol and triglyceride levels and while reducing levels of HDL cholesterol.
Recently, the FDA banned trans fats from the U.S. food supply. The phasing-out process is expected to take three years. The encouraging news is that many major food suppliers and restaurants have already substituted healthier fats for trans fats.
