The importance of eating right fats

Choosing the right ones, in moderation, is key to your health

Last updated: January 2009

The right fats can make you healthier, happier, and smarter; the wrong fats can increase your risk for cancer, diabetes, heart disease, and other serious diseases. But how do you know which fats are the right ones and how much to consume, especially when the news seems to change as fast as the latest diet fads? Research is ongoing, but new studies and recent guidelines reveal just how important it is to choose not only the right fats, but also the right quantities for you and your family.

Good fats vs. bad

The good

With all the confusing news about fats, you might think it's easier to steer clear of them altogether. Not so. The good fats, including monounsaturated and polyunsaturated, can actually help reduce your risk of heart disease and lower your LDL (bad) cholesterol. And you may be surprised as to what's considered a good fat. For example, monounsaturated fat, the healthiest fat, is found at higher levels in:

  • Olive, canola, and other vegetable oils
  • Nuts like almonds and peanuts (including peanut butter)
  • Avocados (including guacamole)

Polyunsaturated fats are also important to your diet, especially those that contain omega-3 fatty acids (omega-3s), which may decrease your risk of coronary artery disease, may protect against irregular heartbeats, and help lower blood pressure. Polyunsaturated fats are found at higher levels in:

  • Salmon, trout, and herring (high in omega-3s)
  • Soybean and corn oils
  • Walnuts and sunflower seeds

Though the better fats are a necessary part of your diet, they still have the same amount of calories as the bad fats and should also be eaten in moderation. The American Heart Association (AHA) recommends that fats (mostly unsaturated) make up 25 to 35 percent of your daily diet-but only 7 percent of those should be fats on the "bad" list.

The bad

Bad fats (saturated and trans fats) have that reputation for good reason. They can raise your blood cholesterol level and increase your risk of heart disease and stroke. Saturated fats come mostly from animal sources and include meats, cheeses, butter, and some plant oils like coconut and palm oil. Unless your doctor has told you to steer clear of saturated fats altogether, the AHA's recommended 7 percent-if you eat approximately 2,000 calories a day, that's only 140 calories or 16 grams-is a good guide. Consult with your doctor or the AHA's My Fats Translator to calculate the right fat ratio for your body type and level of exercise.

Trans fats rarely occur naturally, are mostly manufactured by food companies to preserve foods and add texture and taste to them, and have no nutritional value. Baked goods, pie crusts, cookies, crackers, margarine, and shortening may contain trans fats; try to avoid them by reading product labels.

One of the most popular trans-fat culprits is french fries made in deep fryers at fast-food restaurants. Though many fast-food restaurant chains have eliminated trans fat, and some cities like New York and states like California have or will soon ban them altogether, beware of "trans-free" restaurants. They may still purchase fries and other foods previously fried in trans fat. It's best to be wary of restaurant-fried foods since they pack a lot of calories, no matter what they're fried in.

Fats and weight loss

Cutting the fat doesn't necessarily lead to weight loss. Cutting calories and increasing exercise counts more. While reducing the amount of fat you eat contributes to weight loss, some fatty foods that contain protein remain an important part of your diet. And as an added benefit, they may make you feel fuller longer. A recent study of mice and rats that ingested a fatty acid called oleic acid, found commonly in olive oil and other unsaturated fats, showed that once the fat reaches the intestine it can create a feeling of fullness and prolong the need to eat again. The study has not yet been done in humans, but findings may lead to better insight into how healthy fats help regulate body weight.

Indeed, most research suggests that people who eat moderate amounts of fat are at least as successful at losing weight as those who restrict fat intake sharply. For example, the National Weight Control Registry, which tracks 6,000 successful dieters nationwide, reports that members now consume more fat than previous members did—typically 30 percent of calories from fat compared with 24 percent about a decade ago. Yet registry members are still successfully keeping the weight off. So, provided you keep your total calorie count down and exercise regularly, eating a moderate amount of the right type of fat is recommended.

Your brain on fat

The good fats aren't only good for your heart; new studies show they're also good for your brain, especially polyunsaturated fats containing omega-3s. In one recent study, girls who ate omega-3s actually outsmarted girls who ate higher amounts of omega-6 fatty acids. And scientists believe that women of childbearing age and pregnant and breastfeeding women who store and continue to eat omega-3s supply nutrients that are critical to fetal and early infant brain development. But pregnant and breastfeeding women should continue to balance the need for omega-3s with the risk of eating fish containing mercury.

Omega-3s have also been shown to help people with depression. One 2007 study out of Norway showed that nearly 22,000 people with depressive disorders who took daily doses of cod liver oil, which is high in omega-3s, experienced less depressive symptoms. Another study found depleted levels of omega-3 fatty acids in people with severe depression. And researchers suspect that women who have low levels of omega-3 during pregnancy may be more prone to pregnancy-related depression.

Fats and cancer

Eating too much fat can also put you at risk of developing certain cancers. A recent study by the World Cancer Research Fund and the American Institute for Cancer Research found that a lack of good nutrition and physical activity are proven risk factors for certain cancers. The study also provided dietary recommendations. For example, because diets high in red meat are a risk for developing colon cancer, experts recommend eating no more than 18 ounces per week (preferably less), and avoiding processed meats that are smoked, salted, cured, or contain chemical preservatives.

The report does not advise eliminating meat altogether, but recommends a diet low in red meat and high in non-starchy vegetables, fruits, and whole grains. And it emphasizes that a low-fat diet combined with a healthy weight and regular exercise can reduce your risk of several cancers, including those of the breast, colon, esophagus, kidney, and pancreas.

Women are more prone to breast and ovarian cancers when they have a family history, genetic factors, and have experienced previous cancers, but new evidence suggests that diets high in fat may be another risk factor for post-menopausal women. For example, 2007 findings from the Women's Health Initiative, a large, long-term study dedicated to major health conditions affecting nearly 49,000 postmenopausal women, show that women who ate a low-fat diet had fewer new cases of ovarian cancer than women who had higher-fat diets. And findings from the National Institute of Health and the American Association of Retired Persons combined study of nearly 189,000 postmenopausal women found that women who had higher-fat diets, especially those high in saturated fats, had an increased risk for breast cancer.

These studies don't claim that fats alone cause cancer, but they do demonstrate that high-fat diets can be a risk factor.

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