How can I identify and avoid bad fats?

Michael T. Murray, ND
Naturopathic Medicine
Despite its important role, fat is often considered bad because any extra dietary fat is converted to body fat and stored in fat cells. Since the human body has an almost unlimited capacity to store fat, eating a diet too high in fat can lead to obesity. We recommend a diet that supplies less than 30 percent of calories as fat. However, just as important as the amount of fat is the type of fat you consume. The goal is to decrease your total fat intake, especially your intake of saturated fats, trans-fatty acids (also called hydrogenated fats), and omega-6 fats, while increasing your intake of omega-3 fatty acids and monounsaturated fatty acids.
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Ronald Tamler, MD
Endocrinology Diabetes & Metabolism
There are two main types of potentially harmful dietary fat: 
  • Saturated fat, which comes mainly from animal sources, raises total blood cholesterol levels and low-density lipoprotein (LDL) cholesterol levels, which can increase your risk of cardiovascular disease and type 2 diabetes. 
  • Trans fat is made during food processing through partial hydrogenation of unsaturated fats. This process creates synthetic fats, which can increase unhealthy LDL cholesterol and lower healthy high-density lipoprotein (HDL) cholesterol, increasing your risk of cardiovascular disease.
Dr. Vonda Wright, MD
Orthopedic Surgery
Bad and unhealthy fats are the saturated and trans fats. Saturated fats are solid at room temperature and should be avoided in large amounts. Both saturated and trans fats are correlated with increased risk of heart disease. Examples of these bad fats include butter, whole milk, cheese, cream, coconut oil, margarine, and the fat on meat or lard.
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Emilia Klapp
Nutrition & Dietetics
Our bodies need fat to function. It maintains healthy skin, provides the calories we need for energy and warmth, and supplies insulation and padding for our internal organs. It transports vitamins A, D, E, and K through the blood and helps them to be absorbed in the intestines.

In addition, the body needs fat to produce hormones, which are chemical substances that control bodily functions. Studies show that the type of fat we eat is more important than the amount. A low-fat diet high in saturated fat or trans fats would be more harmful to the arteries than a diet high in the healthy fats found in olive oil.
Anthony L. Komaroff, MD
Internal Medicine
Saturated fat, derived primarily from animal products, clogs arteries and raises the risk for coronary artery disease. Even worse are trans fats, which pack a double whammy by raising harmful low-density lipoprotein (LDL) cholesterol and lowering protective high-density lipoprotein (HDL) cholesterol. Trans fats can be found in foods made with partially hydrogenated oils, such as solid stick margarines, crackers, cookies, snack foods, and other prepared foods. Fast-food restaurants may also fry their foods in partially hydrogenated vegetable oil. The Food and Drug Administration (FDA) has required that trans fats be listed in the "Nutrition Facts" label on food packages. The American Heart Association (AHA) recommends limiting your trans fat intake to less than 1% of your total calories.
Rose Reisman
Nutrition & Dietetics
The unhealthiest fats are saturated and trans fats. Saturated fats come mostly from animal fats and some vegetable sources such as palm and coconut oils. Trans fats are man-made fats created by changing unsaturated fats into saturated fats through a process of heat and hydrogenation. An example is liquid vegetable oil processed into a solid, such as shortening or margarine. These fats are linked to increased insulin production, slower metabolisms and high levels of cholesterol. Many food manufacturers and fast food restaurants are trying to eliminate trans fats from their foods.
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F. Michael Gloth, III
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Not all fats are the same. There are essential fats, and there are fats that should be avoided. Saturated fat has been linked to an increase in low-density lipoprotein or LDL, which has been associated with what many people call "bad cholesterol." Monounsaturated and polyunsaturated fats result in more high-density lipoprotein or HDL, which is related to what is commonly called "good cholesterol." It is the ratio of LDL to HDL that determines risk for cardiovascular disease. Low LDL and high HDL create a ratio linked to a reduction in heart disease.

Another type of fat is trans-unsaturated fatty acids (trans-fats). These artificial fats are man-made by the partial hydrogenation of liquid vegetable fats (oils). This process causes the oils to solidify. The resultant trans-fats are found in margarines and many baked goods and fried foods. Trans-fats raise LDL and triglycerides at the same time they reduce HDL. Thus, they create the worst of all conditions for developing heart disease.
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Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
The simplest way to identify and avoid bad fats is to stay away from fats that are solid or semi-solid at room temperature. These are likely to be fats that are highly saturated or contain trans fats -- both of which are bad for your heart and your health. Such "solid" fats include butter, milk fat, beef fat, chicken fat, cream, pork fat, stick margarine and shortening. They're often found in baked goods, high-fat cheeses, ice cream, French fries, cuts of meat with visible marbling and fried chicken. To eat a healthy diet, you don't need to avoid these foods entirely. But cutting back on them will help you reduce the amount of unhealthy fat in your diet.
"Bad" fats are typically solid at room temperature, such as fat found in butter, lard, and fat trimmed off your meat. Checking food labels and limiting foods that contain fat primarily from saturated fat or trans fat, will help you to make better food choices. 
You want to avoid or limit saturated fats. Saturated fat comes from animal sources, whole milk dairy products, and some oils. Saturated fat is found in red meat, butter, cheeses, luncheon meats, cocoa butter, coconut oil, palm oil, and cream. Saturated fats boost total cholesterol by elevating harmful LDL cholesterol.

 Trans fats are perhaps the worst fats of all. They are formed when unsaturated vegetable oils are hydrogenated to make them solid at room temperature (stick margarine). In the ongoing Nurses’ Health Study, researchers found that among 80,000 women aged 34 to 59, trans fats greatly increased the risk for coronary heart disease. In these findings, researchers reported each 2 percent increase in trans fat calories raised the women’s coronary risk by 93 percent.

Avoid high trans fat foods such as fried foods, snack and fast‑food products, commercial breads, crackers, pastries, and many processed foods.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.