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Dietary fats: The good, bad and worst

What works great in the kitchen doesn't always work so well in your body. Get up to speed on fats' effects on good and bad cholesterol, eliminating trans-fats and more.

In the culinary arts, fats make food taste good. In the medical arts, it isn't so simple. Some fats, namely mono- and polyunsaturated fats, are good for long-term health. Other fats, namely saturated and trans fats, aren't so good and, in fact, can be downright unhealthy. The collision between what's good in the kitchen and what's good in the body poses problems for restaurants across the country.

Dietary fats affect many systems in the body, from energy production to maintaining healthy skin. A key concern is how they affect the heart and blood vessels.

Over the past 50 years, recommendations on which dietary fats are okay, and how much of each type to eat, have swung back and forth. The American Heart Association's first nutrition recommendations in the late 1950s stated that the ratio of saturated to unsaturated fat was probably important. At the time, the AHA recommended that people eat less saturated fat and more unsaturated fat. Following the discovery of the "cholesterol connection," experts and educators decided that the American public couldn't grasp a nuanced idea such as some fats are good and some are bad.

Instead, they promoted an "all fats are bad" message and urged us to lower fat intake across the board to under 20 percent of calories. That was akin to throwing out the baby with the bathwater. Unsaturated fats are actually good for the heart. And mounting evidence shows that eating low-fat foods rich in refined carbohydrates in place of fats isn't any better for the heart—and may be worse. Ongoing research in both areas is moving the pendulum back to a middle position.

Fat's effects on good and bad cholesterol  

Transporting fats from the stomach and intestines to the furthest reaches of the body takes some doing, since fats don't dissolve in blood any better than they do in water. The process is a bit like making mayonnaise—fats are emulsified and stuffed into protein-bound packages called lipoproteins. The larger, fluffier packages, mainly low-density lipoprotein (LDL, or bad cholesterol), can lodge in arteries and damage them. A smaller, more compact package, called high-density lipoprotein (HDL, or good cholesterol), actually scavenges LDL particles from the bloodstream and artery walls and ferries them back to the liver for disposal.

All parts of the body, including the heart and blood vessels, need some saturated fat, and even some cholesterol. But a diet rich in saturated and trans fats leads to the accumulation of LDL in artery walls. Like sharks scenting blood, white blood cells called monocytes drop out of the bloodstream, cluster around trapped LDL, and gorge on it. This is the start of plaque: deposits of LDL, white blood cells and other debris that pock the inside of arteries. Plaque can block blood flow; worse, it can break apart and ooze its contents into the bloodstream. The blood clots that form to stop the leakage can block a blood vessel. When this happens in an artery that feeds the heart, a heart attack ensues. When it happens in the brain, it triggers a stroke.

Trans fats are a byproduct of stabilizing liquid vegetable oil by adding hydrogen. The result, partially hydrogenated oil, doesn't spoil as easily as nonhydrogenated fats. It can also withstand repeated heating without breaking down. These characteristics have made partially hydrogenated oils a mainstay in margarines, commercially baked goods, snack foods, and in restaurants for deep frying.

Saturated fats increase the amount of LDL in the bloodstream. So do trans fats. But trans fats also lower levels of HDL, something saturated fats don't do. Worse, trans fats increase the tendency of blood platelets to form clots in the heart, brain and elsewhere. In a study of female nurses, those who ate 7 grams of trans fats a day were 50 percent more likely to have developed heart disease over a 14-year period than those who ate 2 grams a day. Harvard researchers estimate that replacing trans fats with unsaturated fats could prevent 72,000 to 228,000 heart attacks and deaths each year.

Results from a variety of scientific studies show that changing the amounts of bad and good cholesterol can pay off for the heart.

  • Every 10 percent decrease in LDL reduces heart attack and stroke risk 10 percent.
  • Every 10 percent increase in HDL reduces heart attack and stroke risk 20–30 percent.

Replacing saturated fats with monounsaturated and polyunsaturated fats can lower LDL levels. Cutting back or eliminating trans fats can lower LDL and boost HDL.

Getting rid of trans-fats 

Trans fats contribute 4 percent to 7 percent of calories from fat. Yet for many years they were largely invisible, detected only by people who knew that the terms "partially hydrogenated vegetable oil" or "vegetable shortening" in a list of ingredients indicated their presence.

After a lengthy review, the Food and Drug Administration mandated that starting Jan. 1, 2006, food labels must list trans fats along with total and saturated fats. A number of U.S. companies, including Kraft, Cargill and Frito-Lay, have responded to this rule by working to remove trans fats from their products. On the restaurant front, upscale restaurants as well as some quick service restaurants have switched to trans-free oils for deep frying. Early adopters included Legal Sea Foods and Ruby Tuesday.

McDonald's, which had pledged to cut back on the use of partially hydrogenated oils in 2002, hasn't yet fulfilled that promise. Interestingly, in countries such as Denmark, which restrict the use of trans fats, McDonald's and other American-based quick service restaurants now use trans-free cooking oils. Efforts by the New York City health department to encourage all city restaurants to stop serving food containing trans fats could have a profound effect on the switch to trans-free oils in New York and elsewhere.

One of the problems for restaurant owners has been the availability of trans-free oils and products. So far, there are few good alternatives to solid fats such as margarine or vegetable shortening for baking. Some restaurants and bakeries have shifted to palm and coconut oil, or blends. Oils for deep frying pose another problem. Although major suppliers such as Cargill, Archer Daniels Midland, Monsanto and Dow Agrosciences have low-trans or trans-free oils on the market, the demand is outstripping the supply. Suppliers are also looking for trans-free alternatives for par-frying.

Fish and nuts

Two foods deserve special mention when talking about dietary fats—fish and nuts. Both are rich in healthy omega-3 unsaturated fats, and there is clear and compelling evidence that both can help protect the heart.

The American Heart Association currently recommends eating fish twice a week. That advice is based on five U.S. studies showing that people who eat this much fish are 40 to 50 percent less likely to die of heart disease than those who rarely eat fish.

One way the omega-3 fats in fish do this is by somehow preventing the rise or spread of erratic heart rhythms that can quickly stop the heart from pumping blood to the brain and body. They may also make blood less "sticky" and likely to clot. Fish and the omega-3 fats they contain also seem to help after a heart attack or stroke. In the Diet and Reinfarction Trial, for example, volunteers advised to eat fatty fish like salmon twice a week had a 29 percent reduction in deaths from any cause over a two-year period compared with those who weren't advised to eat more fish.

Nuts offer similar benefits. Studies that included about 260,000 people generally came to the conclusion that regular consumption of nuts is linked with a reduced risk of heart disease. In the Harvard-based Physician's Health Study, for example, men who ate nuts two or more times a week were 47 percent less likely to have died suddenly of cardiac causes than those who rarely ate nuts. This response has been seen in a variety of populations, including men, women, Caucasians, African Americans, the elderly and individuals with heart disease. The more times per week you eat nuts, the lower your risk of heart disease.

Nuts may also help prevent the development of type 2 diabetes, an increasingly common condition among American adults. Among more than 80,000 women followed for 16 years, those who ate nuts five or more times a week were 27 percent less likely to have developed type 2 diabetes than those who rarely ate nuts.

The bottom line

Fats are an essential part of our diet and our food. They provide fuel and building blocks for all parts of the body. They are also an indispensable element for food preparation. The low-fat advice promoted by many of the major health groups during the latter part of the 20th century overlooked the evidence that unsaturated fats are good for the heart, blood vessels and rest of the body, and underestimated the hazards of trans fats.

The latest recommendations from the American Heart Association, as well as the newest Dietary Guidelines for Americans, reflect the changing nature of advice on dietary fats. They no longer advise aiming for a total fat intake under 20 percent of calories. Instead, they say that a healthy dietary pattern can include up to 35 percent of calories from fat as long as most of the fats are healthy, unsaturated fats. At the same time, the guidelines urge us to keep saturated fat intake to under 7 percent of calories, severely limit trans fat intake (to under 1 percent of calories), and limit cholesterol to under 300 milligrams a day by choosing lean meats and vegetable alternatives, fat-free (skim) or low-fat dairy products, and minimizing intake of partially hydrogenated fats.

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