Until recently, the first prerequisite of a healthy diet was to control the intake of total fat, which supplies about 34 percent of total calories in the average American diet. Most experts recommend that you get no more than 25 to 35 percent of your daily calories from fat. Some experts have suggested that total fat intake should be less than 20 percent of daily calories.
But for most people, such a reduction is probably not necessary. According to the American Heart Association (AHA), short-term studies show that a very low fat intake does not reduce "bad" LDL cholesterol much further than a standard low-fat diet. A diet very low in fat contains a greater proportion of carbohydrates, so it has the potential to raise triglyceride levels and lower "good" HDL cholesterol, especially in people who are overweight.
Increasingly, nutrition researchers are emphasizing that the type of fat you consume has more important health consequences than your intake of total fat. In particular, researchers have found a strong link between blood cholesterol and the intake of saturated fat. Your intake of dietary cholesterol can also increase levels of total cholesterol and LDL, but not nearly as much as your intake of saturated fat. Both saturated fat and dietary cholesterol are found in animal foods such as meats, poultry and dairy products.
Replace saturated fats with unsaturated fats
Unsaturated fats do not raise cholesterol levels. In fact, they can lower LDL cholesterol when used in place of saturated fats in your diet. Omega-3 fatty acids, a type of polyunsaturated fat, seem to have additional cardioprotective effects.
Oils rich in unsaturated fats can help maintain healthy levels of both LDL and HDL. Olive and canola oils, almonds and avocados are good sources. Calories from monounsaturated fat can contribute up to 20 percent of total calories.
Up to 10 percent of your total calories should come from polyunsaturated fats, which are found in such foods as corn, safflower, sunflower, walnut, flaxseed and soybean oils. Studies have shown that substituting this type of fat for saturated fat can reduce the risk of coronary artery disease (CAD). Polyunsaturated fats can also lower beneficial HDL cholesterol, but only when intake is very high.
Substituting polyunsaturated fats for saturated fats in your diet is the single most effective dietary measure you can take to prevent high LDL cholesterol or to lower LDL that is already too high. Extensive research indicates that, on average, for every one percent increase in total calories from saturated fat, LDL cholesterol rises about two percent. Conversely, reducing intake of saturated fat by one percent will lower LDL levels by about two percent.
Limit saturated fat
New 2013 guidelines for diet and lifestyle from the American College of Cardiology/American Heart Association (AHA) recommend a saturated fat intake of no more than five to six percent of total calories. (Previously the AHA had set a limit of less than seven percent.) But these lower levels have not been adopted by the U.S. Dietary Guidelines, and many experts do not consider such low targets well justified.
In addition to animal products, saturated fat is found in tropical oils such as palm oil, palm kernel oil and coconut oil—though the health effects of these oils are being debated. Some studies have shown that palm oil and coconut oil have no effect on blood cholesterol. Either one is a better choice than palm kernel oil, which is more saturated and has been less studied.
Limit dietary cholesterol
Cholesterol is found in animal products, and that includes egg yolks. Just because a food is high in cholesterol doesn’t mean that it’s high in fat. For example, shrimp are high in cholesterol and low in fat. Plant foods contain no cholesterol.
The National Cholesterol Education Program and AHA advise no more than 300 milligrams of cholesterol intake a day for healthy people. But some researchers think that these guidelines are too strict and that healthy people can consume more—perhaps as much as 500 milligrams per day. For those whose LDL cholesterol is 160 mg/dL or higher or who have CAD, diabetes or other risk factors for CAD, the recommended limit for dietary cholesterol is 200 milligrams per day.
Avoid trans fats
By now most Americans have heard of trans fats, supplied by the partially hydrogenated oils found in many processed foods and used in preparing many fast foods. Hydrogenation (and partial hydrogenation) transforms many of the oils’ unsaturated fatty acids, making them more saturated and altering their chemical structure in other subtle ways. Like saturated fats, these trans fatty acids, or trans fats, raise total and LDL cholesterol. What appears to make them even worse than saturated fat is that they also lower HDL cholesterol. Studies have linked them with heart attacks, strokes, diabetes and other diseases.
Thankfully, food makers and restaurants have been making efforts to remove trans fats—and their efforts have yielded healthier products, for the most part. A study of 83 reformulated foods, reported in a letter in the New England Journal of Medicine in 2010, found that 65 percent of the supermarket products and 90 percent of the restaurant products had levels of saturated fat that were lower, unchanged or only slightly higher than before. Often, the partially hydrogenated oils were replaced by heart-healthy unsaturated oils.
Published February 20, 2014