Dietary Fats: The Good, the Bad, and the Worst
In the culinary arts, one simple fact is this: fats make food taste good. In the medical arts, it isn't so simple. Some fats, namely saturated and trans fats, aren't so good for long-term health. Other fats, namely mono- and polyunsaturated fats, are good for long-term health.
While fats affect many systems in the body, from energy production to maintaining healthy skin, nutritionists are mainly interested in their effects on the heart and blood vessels. Healthy muscles and blood vessels need some saturated fats and even some cholesterol—but not too much. A diet rich in saturated and trans fats can cause one type of fat- and protein-carrying particle known as low-density lipoprotein (LDL, or bad cholesterol) to accumulate in artery walls.
These pockets, known as plaque, can enlarge to the point where they block blood flow. Even worse, they can break apart and ooze their contents into the bloodstream. When this happens, 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.
Changing Recommendations on Fat Intake
Over the past 50 years, recommendations on which dietary fats are okay, and how much of each, has swung back and forth. In the American Heart Association's (AHA) first nutrition recommendations in the late 1950s, the organization stated that both fat and total calories were probably important in the development of heart disease, and that the ratio of saturated to unsaturated fat was probably important. At the time, the AHA recommended that people eat less saturated fat and eat more unsaturated fat. After the discovery of the "cholesterol connection," experts and educators decided that the American public couldn't grasp a nuanced idea such as good and bad fats. Instead, they promoted an "all fats are bad" message, and urged us to lower fat intake across the board. That was akin to throwing out the baby with the bathwater. Mounting evidence showing that unsaturated fats are actually good for the heart, along with the realization that eating refined carbohydrates in place of fats isn't any better for the heart—and may be worse—is moving the pendulum back to a middle position.
Current dietary guidelines now call for curbs on saturated and trans fats, and are silent on unsaturated fats or promote their use. For example, the latest iteration of the Dietary Guidelines for Americans says to "choose fats wisely for good health." According to the guidelines, this means keeping saturated fat intake below 10 percent of calories, trans fat intake below one percent of calories, and cholesterol intake below 300 milligrams per day. The guidelines acknowledge that Omega-3 unsaturated fats, found mainly in fish, are good for the heart. It also "allows" a wide range of fat intake, from 20 to 35 percent of calories.
Effects of Different Fats on Good and Bad Cholesterol
Getting fats from the stomach and intestines to the furthest reaches of the body takes some doing; fats don't dissolve in blood any better than they dissolve in water. So, a bit like you might make mayonnaise, fats are emulsified and stuffed into protein-bound packages called lipoproteins. The larger, fluffier packages, like low-density lipoprotein (often called LDL, or bad cholesterol) can lodge in arteries and damage them. Smaller, more compact packages, like high-density lipoprotein (often called HLD, or good cholesterol), actually scavenge LDL particles and ferry them back to the liver for disposal. Different dietary fats have different effects on LDL and HDL.
Eliminating Trans Fats
Trans fats are mostly man-made fats that have, quietly, become a substantial part of the American diet. These stealth fats—they aren't currently listed on food labels—contribute four to seven percent of calories from fat. They're abundant in many margarines, vegetable shortenings, fast-food french fries, donuts, commercial baked goods such as packaged pastries and cookies, and countless other foods. The only way you know they are in a product is the term "partially hydrogenated vegetable oil" or "vegetable shortening" in the list of ingredients.
Trans fats raise levels of LDL (bad) cholesterol, just like saturated fats do. But they also lower levels of HDL, the protective form of cholesterol, something that saturated fats don't do. To make matters worse, trans fats make blood cell fragments—platelets—stickier than usual, and more likely to form clots inside blood vessels in the heart, brain, and elsewhere. These changes result in more heart disease. In a long-term study of female nurses, for example, those who ate the most trans fats (about seven grams a day) were 50 percent more likely to have developed heart disease over a 14-year period than those who ate the least (about two grams a day).
Not long ago, a Food and Drug Administration (FDA) advisory panel said that trans fats are even more harmful than saturated fats. The Institute of Medicine went a step further, concluding that the safest amount of trans fats for humans is zero. Here's what FDA Commissioner Mark McClellan had to say about trans fats:
Considerable recent research, including controlled feeding and epidemiological studies, has provided pretty good evidence that replacing saturated and trans fats with mono- and poly-unsaturated fats can significantly reduce important health risks. According to some studies, this substitution can potentially reduce the risk of heart disease by up to 30-40 percent.
After a lengthy review, the FDA decided that starting Jan. 1, 2006, food labels must list trans fats along with total and saturated fats. Some U.S. companies have responded to this rule by removing trans fats from their products. On the restaurant front, a number of upscale and quick service restaurants have switched to liquid vegetable oil, which is free of trans fats, for deep frying. Others continue to use trans-rich partially hydrogenated shortening for deep frying. Interestingly, in countries such as Denmark, which restrict the use of trans fats, several American-based quick service restaurants now use trans-free cooking oils.
Out With the Bad, In With the Good
Results from different types of scientific studies show that changing the amounts of bad and good cholesterol in the body can pay off for the heart.
- Every 10 percent decrease in LDL (bad) cholesterol reduces heart attack and stroke risk by 10 percent.
- Every 10 percent increase in HDL (good) cholesterol reduces heart attack and stroke risk by 20–30 percent.
Dietary changes can nudge LDL and HDL in the right directions. Cutting back on saturated fats and replacing them with monounsaturated and polyunsaturated fats can lower LDL levels. Cutting back or, even better, eliminating trans fats can lower LDL and boost HDL.
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 40–50 percent less likely to die of heart disease than those who rarely eat fish.
The Omega-3 fats in fish seem to work 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.
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.