Whether you are considering a low-carb, high-fat diet or a more conventional higher-carb, low-fat diet, you will have fat in your diet. Are all fats the same? For many years fat in the diet has been demonized. Grocery stores are filled with foods labeled "low fat." In the past twenty years, Americans have reduced the percentage of calories that we get from fat. However, the total calories and grams of fat we consume have actually increased and remain substantially higher than in most places in the world. What have we been told is wrong with fat? We've been told that there are more calories in each gram of fat than in each gram of carbohydrate 146, or protein, which is true. But the impression has been left that, calories aside, all fats are bad for you because they increase the chance of heart disease and other diseases. That is not true.
We need fat in our diet to provide fuel for the body's cells and to build the membranes around every cell. Not all fats are unhealthy. Some fats are good for you. In fact, they are essential for good health. If you eat more healthy fats—and stay away from unhealthy ones—you can improve your health. But don't lose sight of the main target: keeping your weight in a healthy zone.
There are several different types of fats in our diet. Two of them are particular problems: saturated fats and trans fats. Fats that are saturated (referring to their full saturation with, and inability to accept any more, hydrogen atoms) are abundant in meat and animal fat, dairy products, and some oils such as palm and coconut oil. They are solid rather than liquid at room temperature. Saturated fats in the diet indisputably increase the artery-clogging process known as atherosclerosis, primarily by increasing blood levels of LDL ("bad") cholesterol.
Trans fats are largely created by manufacturing, not by nature. They were created by industrial chemists who were asked to find a way of transforming liquid oils into solids, so that they would be easier to ship, and to protect the oils against becoming rancid. Trans fats have rapidly increased in our diets, finding their way into commercial baked goods, fast-food french fries, margarine, and vegetable shortenings such as Crisco. Starting in 2006, the Nutrition Facts food labels will contain the amount of trans fats in each grocery store food. Until then, look for the words partially hydrogenated vegetable oil or shortening on the food label; when you see it, you know there are trans fats present. The problem with trans fats is that they increase heart disease, stroke, and other diseases caused by atherosclerosis—like saturated fats.
Two types of fats in the diet that are good for you: monounsatu-
rated and polyunsaturated. (Unsaturated refers to a chemical struc- ,147
ture that can accept one or more hydrogen atoms.) The monoun-saturated fats that we use most often are found in certain oils, particularly olive, peanut, and canola oils. The polyunsaturated fats are called "essential" fats because our bodies do not make them; we must get them in our diet. The most common sources of polyunsaturated fats are plant oils such as corn and soybean oil, seeds, whole grains, and fatty fish such as salmon and tuna.
You will hear about two types of polyunsaturated fats: n-3 (also called omega-3) fats and n-6 (also called omega-6) fats. There is some controversy about whether they are equally good for you and whether the ratio of one to the other is important. In our view, the main point is that they are both healthy for you.
The healthy fats do several important things for you. First, they have the opposite effect of the saturated fats and lower your blood levels of LDL ("bad") cholesterol, reducing your risk of developing atherosclerosis. The n-3 polyunsaturated fats also reduce the chance that—if you have heart disease (including heart disease that has not caused symptoms and been diagnosed)—you will develop life-threatening problems with the rhythm of your heart. There are also data demonstrating a beneficial effect on inflammation and other vascular changes that seem to underlie atherosclerosis and heart disease.
A large study called the Lyon Diet Heart Study, conducted in France, provided strong evidence that adding monounsaturated fats and polyunsaturated fats to the diet protected against atherosclerosis and lengthened life. This randomized controlled trial assigned some people to eat a "Mediterranean" diet including more vegetables, more fruit, more fish and poultry, less red meat, and no cream. The people eating the Mediterranean diet also were given a special margarine that was low in saturated and trans fats and rich in unsaturated fats, especially the essential n-3 polyunsaturated fat known as alpha-linolenic acid. The results of the Lyon Diet Heart Study were unusually dramatic and clear: after only two and a half years, there was a 70 percent reduction 148, in deaths from all causes.
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