The Skinny on Fat: Good Fats vs. Bad Fats
How fats fit into your healthy diet.
By Kathleen Zelman, MPH, RD/LD
WebMD Weight Loss Clinic - Feature
Reviewed By Louise Chang, MD
Fat, fat, fat! Would all of our weight loss problems be solved if we just eliminated fat from our diets? Unfortunately, it's not that simple. We actually need fats -- can't live without them, in fact. Fats are an important part of a healthy diet: They provide essential fatty acids, keep our skin soft, deliver fat-soluble vitamins, and are a great source of energizing fuel. But it's easy to get confused about good fats vs. bad fats, how much fat we should eat, how to avoid artery-clogging trans fats, and the role omega-3 fatty acids play in heart health.
The U.S. Department of Agriculture's 2005 Dietary Guidelines recommend that adults get 20%-35% of their calories from fats. At a minimum, we need at least 10% of our calories to come from fat.
The problem is that the typical American diet is higher in fat: Roughly 34% to 40% of our calories come from fat. Why? Because they taste so good and are widely available in our food supply. Fats enhance the flavors of foods and give our mouths that wonderful feel that is so satisfying.
Does Dietary Fat Make You Fat?
So you might assume that fat is to blame for the obesity epidemic now plaguing our nation. Actually, fat is only part of the problem. Obesity is much more complicated than just overeating a single nutrient. Eating more calories -- from fats, carbohydrates, protein, and alcohol -- than you burn off leads to weight gain. Simply put, people who get little physical activity and eat a diet high in calories are going to gain weight. Genetics, age, sex, and lifestyle also weigh into the weight-gain formula.
That said, dietary fat plays a significant role in obesity. Fat is calorie-dense, at 9 calories per gram, while carbs and protein have only 4 calories per gram, and alcohol has 7 calories per gram. It's easy to overeat fats because they lurk in so many foods we love: french fries, processed foods, cakes, cookies, chocolate, ice cream, thick steaks, and cheese.
"Choosing the right types of dietary fats to consume is one of the most important factors in reducing the risk of developing heart disease," says Tufts University researcher Alice Lichtenstein. DSc.
But while choosing healthier fats is better for your heart, when it comes to your waistline, all fats have about the same number of calories. And cutting the total fat in your diet not only helps you shed pounds, it can also help you live longer and healthier.
"There is a strong association between being overweight and many types of cancer, especially breast cancer among postmenopausal women, and colon cancer," says Colleen Doyle, MS, RD, nutrition and physical activity director for the American Cancer Society.
"Eating less total fat will not directly lower your cancer risk, but it will help you control your weight -- which in turn can reduce your risk of cancer."
Good Fats vs. Bad Fats
Basically, there are two groups of fats: saturated and unsaturated. Within each group are several more types of fats.
Let's start with the good guys -- the unsaturated fats. Unsaturated fats include polyunsaturated fatty acids and monounsaturated fats. Both mono- and polyunsaturated fats, when eaten in moderation and used to replace saturated or trans fats, can help lower cholesterol levels and reduce your risk of heart disease.
Polyunsaturated fats, found mostly in vegetable oils, help lower both blood cholesterol levels and triglyceride levels -- especially when you substitute them for saturated fats. One type of polyunsaturated fat is omega-3 fatty acids, whose potential heart-health benefits have gotten a lot of attention.
Omega-3s are found in fatty fish (salmon, trout, catfish, mackerel), as well as flaxseed and walnuts. And it's fish that contains the most effective, "long-chain" type of omega-3s. The American Heart Association recommends eating 2 servings of fatty fish each week.
"Plant sources are a good substitute for saturated or trans fats, but they are not as effective as fatty fish in decreasing cardiovascular disease," notes Lichtenstein. Do keep in mind that your twice-weekly fish should not be deep-fat fried!
It is best to get your omega-3s from food, not supplements, Lichtenstein says: "Except for people with established heart disease, there is no data to suggest omega-3 supplements will decrease heart disease risk."
The other "good guy" unsaturated fats are monounsaturated fats, thought to reduce the risk of heart disease. Mediterranean countries consume lots of these -- primarily in the form of olive oil -- and this dietary component is credited with the low levels of heart disease in those countries.
Monounsaturated fats are typically liquid at room temperature but solidify if refrigerated. These heart-healthy fats are typically a good source of the antioxidant vitamin E, a nutrient often lacking in American diets. They can be found in olives; avocados; hazelnuts; almonds; Brazil nuts; cashews; sesame seeds; pumpkin seeds; and olive, canola, and peanut oils.
The 'Bad' Fats in Your Diet
Now on to the bad guys. There are two types of fat that should be eaten sparingly: saturated and trans fatty acids. Both can raise cholesterol levels, clog arteries, and increase the risk for heart disease.
Saturated fats are found in animal products (meat, poultry skin, high-fat dairy, and eggs) and in vegetable fats that are liquid at room temperature, such as coconut and palm oils. The 2005 Dietary Guidelines recommend limiting saturated fats to 10% or less of your total calories, while the American Heart Association recommends keeping them to just 7% of total calories.
Lichtenstein recommends using liquid vegetable oils in place of animal or partially hydrogenated fats.
"There is evidence that saturated fats have an effect on increasing colon and prostate cancer risk, so we recommend whenever possible to choose healthy unsaturated fats -- and always strive to be at a healthy weight," Doyle explains.
We're also hearing a lot these days about trans fatty acids, or trans fats. There are two types of trans fats: the naturally occurring type, found in small amounts in dairy and meat; and the artificial kind that occur when liquid oils are hardened into "partially hydrogenated" fats.
Natural trans fats are not the type of concern, especially if you choose low-fat dairy products and lean meats. The real worry in the American diet is the artificial trans fats. They're used extensively in frying, baked goods, cookies, icings, crackers, packaged snack foods, microwave popcorn, and some margarines.
Some experts think these fats are even more dangerous than saturated fats.
"Trans fats are worse than any other fat, including butter or lard," says Michael Jacobson, executive director of the Center for Science in the Public Interest, a nonprofit advocacy group.
Research has shown that even small amounts of artificial trans fats can increase the risk for heart disease by increasing LDL "bad" cholesterol and decreasing HDL "good" cholesterol. The American Heart Association (AHA) recommends limiting trans fat to less than 2 grams per day, including the naturally occurring trans fats. The U.S. Dietary Guidelines simply recommend keeping trans fats consumption as low as possible.
Still, eliminating trans fats is not a magic bullet, experts say.
"Trans fat is getting lots of bad press, but it is important to keep in mind the 'big fat picture,' which includes lowering total fat, reducing saturated fat, and engaging in an overall healthy lifestyle," cardiologist Robert Eckel, MD, tells WebMD.
Which Fat Is Which?
Most foods contain a combination of fats but are classified according to the dominant fat. This chart lists sources of the good-for-you unsaturated fats as well as some examples of fats you want to avoid.
|Saturated Fats or Trans fatty acids||Polyunsaturated Fats||Monounsaturated Fats|
|Butter||Corn oil||Canola oil|
|Lard||Fish oils||Almond oil|
|Meat, lunchmeat||Soybean oil||Walnut oil|
|Poultry, poultry skin||Safflower oil||Olive oil|
|Coconut products||Sesame oil||Peanut oil|
|Palm oil, palm kernel oil and products||Cottonseed oil||Avocado|
|Dairy foods (other than skim)||Sunflower oil||Olives|
|Partially hydrogenated oils||Nuts and seeds||Peanut butter|
Read Labels and Make Better Choices
The best way to keep on top of the fats in your diet is to become a label reader. On the nutrition facts panel, you'll find all the information you need to make healthful choices. Look for foods that are low in total fat and well as in saturated and trans fats. Bear in mind that a product whose label boasts it is "trans fat free" can actually have up to 0.5 grams of trans fats per serving -- and these can add up quickly.
Here are more tips to help you reduce the total amount of fat in your diet and make sure the fats you consume are the healthy ones:
- Choose a diet rich in whole grains, fruits, and vegetables.
- Try a vegetarian meal, with plenty of beans, once a week.
- Select dairy products that are skim or low-fat.
- Experiment with light and reduced-fat salad dressings.
- Replace fattier sauces with vinegars, mustards, and lemon juice.
- When using fats, do so sparingly. Try to use unsaturated liquid oils, such as canola or olive, instead of butter or partially hydrogenated margarine.
- Limit your consumption of high-fat foods, such as processed foods, fried foods, sweets, and desserts.
- When cooking, substitute the lower-fat alternative (for example, low-fat sour cream or low-fat cream cheese) whenever possible
Published October 31, 2007.
SOURCES: WebMD Weight Loss Clinic Expert Column: "The Skinny on Fats." WebMD Weight Loss Clinic Feature: "Trans Fat Free Food: What's the Truth?" Alice H. Lichtenstein, DSc, Gershoff Professor of Nutrition Science and Policy, director and senior scientist, Cardiovascular Nutrition Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University. Robert Eckel, MD, past president, American Heart Association. Michael Jacobson, PhD, executive director, Center for Science in the Public Interest. Colleen Doyle, MS, RD, nutrition and physical activity director, American Cancer Society.
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