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Harvard Commentaries
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Reviewed by the Faculty of Harvard Medical School

Food for Thought Food for Thought

Fat -- Friend Or Foe?

January 16, 2013

By Jill Pluhar, M.S., B.A.
Brigham and Women's Hospital

For over three decades we have been bombarded with messages telling us dietary fat causes obesity, heart disease and high cholesterol. Yet more recently, we have been told that fat is absolutely essential to our health. So, is fat a major cause of disease or is it necessary for our well being? Actually, it's both. The trick is, there are many different types of fat. Depending on which fat you include in your diet, you may help or hinder your health.

The Skinny on Fat

Not all fats are created equal. Some fats can damage your body and promote disease. Others can actually help prevent certain ailments.

Avoid unhealthy trans fat.

Limit saturated fats.

Include health fats, such as monounsaturated and polyunsaturated, which includes omega-3 and omega-6 fatty acids.

Healthy fats are essential for the:

  • Brain: 60% of the human brain is composed of fat.
  • Cells: Fatty acids make up the membranes that surround our cells.
  • Nerves: Fat makes up the material covering our nerves and allows for messages to be passed from one part of the body to another.
  • Digestion: Fat is needed to absorb certain vitamins (A,D,E and K) from our food.
  • Satiety: Fat helps us feel full longer and helps keep us from overeating.
  • Organs: Fat cushions our internal organs and helps protect them.
  • Immune system: Fat can help prevent inflammation and can help boost our immune system.

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Trans Fat

Trans fat is made when vegetable oil is heated in a process known as hydrogenation. The oil becomes more stable and less likely to spoil. As a result, manufacturers like to put this inexpensive fat in food products as a preservative. Trans fats are the "double whammy" of fats because they raise your LDL or "bad" cholesterol and lower your HDL or "good cholesterol."

Food sources

  • Baked goods: Cookies, crackers, cakes, muffins, pie crust
  • Fried foods: Doughnuts, French fries, fried chicken
  • Snack items: Chips (tortilla,corn,potato), microwave popcorn
  • Solid fats: Stick margarine

How to avoid them

  • Limit the amount of baked goods and snack foods made with hydrogenated oils, as well as fried foods, that you eat.
  • Read food labels and look for the words "partially hydrogenated oil." It's the manufacturers' code for trans fat. Even if a food label reads "0 grams trans fat," if you see partially hydrogenated oil on the label, trans fat is in the product. Currently, the government allows manufacturers to list "0 grams trans fat" if there is less than 0.5 gram per serving. The problem is, if you eat enough products with 0.5 gram of trans fat per serving, it can add up to an unhealthy level.

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Saturated Fat

Saturated fat raises your LDL cholesterol, which is a major contributor to heart disease.

Food sources

  • Animal products: Fatty meats, full fat cheeses, butter, whole milk products
  • Other foods: Coconut oil, palm oil

How to limit them

Limit the amount of high-fat animal foods, baked goods and fried foods you eat.

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Monounsaturated and Polyunsaturated Fats

These fats are typically liquid at room temperature. According to the American Heart Association, when eaten in moderation, monounsaturated and polyunsaturated fats can help reduce LDL or "bad cholesterol," which helps lower your risk of heart disease and stroke. Monounsaturated fats also have the benefit of raising your good cholesterol (HDL).

Food sources of monounsaturated fats

  • Vegetable oils: Olive oil, canola oil, peanut oils
  • Other sources: Avocados, peanut butter and other nut butters, nuts such as almonds, pecans, pistachios, peanuts and cashews.

How to get more in your diet

Cook with olive and canola oils; include nuts and nut butters in your snacks.

Food sources of polyunsaturated fats

Polyunsaturated fats include 2 types- omega-3 (linolenic acid) and omega-6 (linoleic acid). Both are essential and not made by the body. Omega-6 fats are effective in lowering cholesterol and reducing the risk of heart disease. Omega-3 fats are noted for their role in normal brain function, growth and development. They also help prevent inflammation, which is associated with certain forms of cancer and heart disease.

Omega-6 food sources

  • Vegetable oils: Corn, soybean, safflower, sunflower, sesame oils

How to get more in your diet

Omega-6 fats are more prevalent in our diets, therefore the emphasis is on adding more omega-3s to balance the type of fats. Avoid hydrogenated fats in your foods. Liquid forms of omega-6 oils are best.

Omega-3 food sources

  • Fish: Salmon,trout,mackerel,sardines,herring, anchovies, canned tuna
  • Walnuts, flaxseed, flaxseed oil, wheat germ

How to get more in your diet

The American Heart Association recommends individuals eat fish high in omega-3s at least twice a week. Eat more nuts and seeds.

In summary, you may help prevent diet-related health problems and improve your overall health by including in your diet monounsaturated fats, and the polyunsaturated fats – omega-6 and omega-3.

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Jill Pluhar has a B.A. in Neuro and Behavioral Sciences from Mount Holyoke College. She has also completed her Master's of Nutriton Science from Oregon State University. Jill recently completed her Dietetic Internship at the Brigham and Women's Hospital and is employed on their staff in the Nutrition Consult Services department.

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