Fat is big. You can barely get through a newspaper or magazine without bumping into it--in foods we like, people we love and diseases we wish to avoid.
Not only is it big, it's complicated and controversial. Every week, reports say, don't eat fat, or if you do, eat so much of this kind, but avoid that one, and measure these types in your blood.
If fat is a blob that is becoming a blur, these pared-down facts may help:
Fat is not a four-letter word.
In fact, it is as essential as protein and carbohydrates--which is why most of us like it so much. Evolution saw to it that we would like ice cream and French fries for a reason.
It is essential in helping the liver to make cholesterol, a waxy, fatty substance that is used to make cell membranes and structures, including nerve and brain cell sheaths (the greatest concentration of cholesterol is actually in the brain); the hormones estrogen and testosterone; vitamin D; bile, which helps digest fats; and skin oils.
Fat also carries and helps the body to absorb vitamins A, D, E and K. It's the body's most efficient source of energy: Every gram of fat delivers nine calories, compared with four each for protein and carbohydrates.
Some fat circulates in the blood--this is what experts are referring to when they talk about triglycerides, which are transportable fuels ferrying vitamins and helping synthesize other hormone-like chemicals. Much of it is stored in adipose tissue, which pads our organs, insulates the body and is a good source of fuel.
Cholesterol, the good, the bad and the clogged.
The fat we eat contributes to most of our cholesterol made in the liver. (Thus, cholesterol-free food may not reduce your cholesterol levels if it's high in saturated fats.) But we also can get cholesterol from animal foods--meat and dairy products. (Plant-based foods don't contain cholesterol.)
Cholesterol is carried away from the liver through the bloodstream by low-density lipoprotein, LDL. High-density lipoprotein, HDL, carries excess cholesterol from different body tissues back to the liver, where it is eventually sent to the intestines.
Too much cholesterol in the blood can clog the arteries, which is why LDL is often referred to as the "bad" cholesterol. In actuality, it is not bad at all, but it apparently moves more slowly than HDL and can drop off bits of cholesterol along the way. These get stuck to artery walls, harden and can eventually stop up the works. Too high an LDL level, then, is a marker that you could be clogging your arteries and risking a heart attack or stroke.
Because HDL clears the body of excess cholesterol--like the cleanup crew--it is often referred to as the "good" cholesterol. The higher your HDL, the better.
Not all fats are alike.
Fats are composed of three fatty acid molecules, made up of carbon, hydrogen and some oxygen, and one glycerol molecule, and are divided into two main groups: saturated and unsaturated, depending on the number of hydrogen atoms.
If the fatty acid contains the maximum quantity of hydrogen atoms, it is saturated. Animal fats--meats and dairy products--and some vegetable oils--coconut and palm oil--are high in saturated fats.
If there are places on the carbon atom that are unoccupied by hydrogen, the fatty acid is unsaturated. When one pair of hydrogen atoms is missing, it is called mono-unsaturated: Oils high in mono-unsaturated fats are canola (made from rapeseed) and olive.
When more than one hydrogen pair is missing, it is called polyunsaturated: Corn, safflower and sunflower oils are high in polyunsaturates.
A trans fat, also called a trans fatty acid or transunsaturated fat, is an unsaturated fat that is artificially saturated with hydrogen--hydrogenated. Food manufacturers hydrogenate unsaturated fats to make them hard at room temperature. Margarine and vegetable shortening are the best examples, although many food products have "hydrogenated oils" on their labels.
The reason saturated fats--and now trans fats--get a bad rap is that they raise levels of LDL in the blood. In fact, saturated fats have a greater effect on raising blood levels of cholesterol than cholesterol you get in your diet. And trans fats, according to a large study published recently in the New England Journal of Medicine, not only raise the LDL level, they appear to lower HDL levels and raise triglyceride levels as well.
Unsaturated fats, on the other hand, do not appear to raise LDL levels. And one type of polyunsaturated fat, the omega 3-fatty acid, found in fish oil, has been found to reduce the process of atherosclerosis--the building up of plaque on the artery walls. However, there is some question about what role, if any, polyunsaturated fats may play in some cancers.
And there is considerable debate about how much you're supposed to get of any of these fats. Stay tuned.
(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
* Food Allergy Network: (800) 929-4040. Web site: http://www.foodallergy.org.
* American Dietetic Assn. Nutrition hotline: (800) 366-1655 in English and Spanish. Web site: http://www.eatright.org.
* American Heart Assn.: (800) AHA-USA1. Web site: http://www.americanheart.org.
* American Diabetes Assn.: (213) 966-2890 serving California and Nevada. Web site: http://www.diabetes.org.
* Milk Processor Education Program: (800) WHY-MILK. Web site: http://www.whymilk.com.