The Skinny on Fat: Good Fats vs. Bad Fats
How fats fit into your healthy diet.
By Kathleen Zelman, MPH, RD/LD
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.
And eating too much fat does more than expand our waistlines. Our love affair with fat has helped to trigger an increase in the rates of type 2 diabetes, certain cancers, and heart disease.
"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!