The Great Fat Debate Continues

Sharon Palmer, R.D.

Environmental Nutrition

"Eat a low-fat diet." That was the public health message 30 years ago -- which turned out to be dead wrong and set off a national fat phobia. Some of the country's leading nutrition experts discussed this decades-old debate about optimal fat intake at a conference last fall. Walter Willet, M.D., Ph.D., chairman of the nutrition department at the Harvard School of Public Health, reported at the conference: "Data in the 1980s found that total fat and coronary heart disease had no co-relationship; it was the type of fat -- not total fat -- in the diet that was important." At that time, research didn't link low-fat diets with energy balance and a lowered risk of type 2 diabetes or breast and colon cancer, either. But that didn't stop health experts from promoting low-fat diets for all.

Three decades ago advice to lower fat came out of an oversimplification of diet recommendations; instead of emphasizing replacing saturated fats with unsaturated fats, the advice was, simply, "lower fat intake." Soon the "eating fat makes you fat" myth took hold and the food industry created "low-fat" everything, from cookies to snack foods. The manufacturers skimmed off part of the fat in their formulations and dumped in refined carbs like white flour and sugar to fill in the flavor gaps. People started reaching for the low-fat version of foods, patting themselves on the back for making a "healthy" decision. And since the low-fat food was "healthy," why not eat the whole box?

Let's take a fresh look at the types of fat and cholesterol and how they impact health.

Total fat.

Dietary fats are a class of nutrients that include specific fatty acids, such as polyunsaturated fatty acids (PUFAs) and monounsaturated fatty acids (MUFAs.) Many foods contain a combination of different kinds of fats. While it's well established that you should no longer obsess over lowering total fat, consider this: Fat contains nine calories per gram (carbs and protein contain four calories per gram), so they are a key factor in maintaining calorie and weight balance. A healthy weight is one of the most important ways to prevent chronic disease. Though science reveals no perfect formula of fat, carbs and protein that leads to the most successful weight loss, there is evidence that dietary patterns relatively low in calorie density -- high in vegetables, fruit, and total fiber and relatively low in total fat and added sugars -- are associated with healthy body weights. The Dietary Guidelines Advisory Committee (DGAC,) a panel of experts tasked with devising guidelines for eating, recommends a total fat intake of 20 to 35 percent of calories for adults, which adds up to 44 to 78 grams (g) for the average person -- with further emphasis on the types of fats within this range.

Saturated fat.

Saturated fats found in animal fats and tropical oils (palm, coconut) have consistently been painted as the "bad guy" of the fat world, but recently that idea has encountered argument. A meta-analysis published in the January 2010 American Journal of Clinical Nutrition showed no significant evidence that saturated fat is linked with increased risk of coronary heart disease (CHD) or cardiovascular disease (CVD.) Dariush Mozaffarian, M.D., Ph.D., associate professor at the Harvard School of Public Health, reported at the conference, "If you replace saturated fats with PUFAs you see an overall benefit. If you replace saturated fats with processed carbs, the risk increases significantly. It's not useful to focus on saturated fats any longer."

But don't stock up on bacon just yet. Linda Van Horn, Ph.D., R.D., chair of the DGAC, said at the conference, "No one advocates higher saturated fats; (rather), the increase in fats should be derived from unsaturated fats." Indeed, the DGAC reports there is strong evidence that saturated fats are associated with increased total and LDL ("bad") cholesterol, insulin resistance, type 2 diabetes and CVD risk. It recommends consuming less than 10 percent of calories from saturated fats (22 g for the average person,) gradually reducing that amount to under seven percent (16 g on average.)

MUFAs and PUFAs.

Strong evidence indicates that if you reduce saturated fats in your diet and replace those calories with MUFAs or PUFAs, you can decrease the risk of CVD and type 2 diabetes risk, because these fats improve the blood lipid profile and the responsiveness of insulin in the body. MUFAs are found in sources like avocados, peanut butter, nuts, seeds and oils such as olive, canola, peanut, sunflower and sesame. PUFAs are found in nuts, seeds, and vegetable oils such as safflower, corn, sunflower, soy and cottonseed oils.

Since Americans consume about 11 percent to 12 percent of their calories from saturated fats, the DGAC recommends that people would benefit from replacing about 5 percent of that fat with MUFAs or PUFAs. That means the average person should swap out about 11 g of saturated fats for MUFAs or PUFAs. It's not hard to do. If you're looking for MUFAs, one tablespoon of olive oil has 10 g, one-fourth of an avocado has 5 g, one ounce of mixed nuts has 9 g, and one tablespoon of peanut butter has 4 g. And just one tablespoon of safflower oil contains 10 g of PUFAs.

Omega-3 fatty acids.

There's no doubt that this type of PUFA is in the healthy fat category, as omega-3 fatty acids have been shown to reduce inflammation and lower the risk of some chronic diseases. The DGAC studied various types of omega-3 fatty acids from whole foods: alpha-linolenic acid (ALA) from plant sources like flax and walnuts, and docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) from seafood sources. It concluded that there is moderate evidence that eating two four-ounce servings of seafood per week, for an average 250-milligram (mg) intake of EPA plus DPA, is linked with reduced sudden death or cardiac mortality from CHD. Since limited evidence indicates that higher amounts of ALA may reduce mortality in people with CVD, the DGAC recommends ALA intake of .6 to 1.2 percent of total calories -- 1.3 to 2.7 g per day for the average person. Two tablespoons of whole flaxseed contains 5.2 g, one ounce of walnuts contains 2.5 g, and one tablespoon of canola oil contains 1.6 g of ALA.

Dietary cholesterol.

Though it's technically not a fat, dietary cholesterol found in animal products such as egg yolks, dairy products and meats can still have an impact on blood lipids. Aim for less than 300 mg per day, or less than 200 mg per day if you are at high risk for CVD or type 2 diabetes, evidenced by elevated LDL cholesterol and/or blood glucose levels. (There's fresh news on eggs, once bashed for their high cholesterol content. Clinical trials show that eating one egg a day is not linked with risk of CHD or stroke in healthy adults.) But if you're at higher risk for CVD or diabetes and aim for 200 mg of dietary cholesterol per day, further reduction of eggs, meat and animal fats may be necessary.

Trans fatty acids.

There's little disagreement that artificial trans fats serve no benefit; they are linked with poor blood lipid profiles and increased risk of CVD. Produced by partially hydrogenating PUFAs so that they become more solid, trans fats were developed to replace saturated fats in products like margarine, snacks, baked goods and fried foods. Even though not enough is known about the effects of trans fats found naturally in small amounts in red meats and dairy products, the DGAC allows for small amounts of the naturally occurring type of trans fat while recommending that we avoid industrial (i.e., added) trans fats altogether.

Choosing Healthy Fats

It's easy to switch out saturated and trans fats for healthy PUFAs and MUFAs.

Instead of this -- Choose this

Marbled cuts of red meat -- Seafood

Bacon -- Avocado

French fries, baked goods -- Nuts

Butter -- Soft margarine containing liquid vegetable oil as first ingredient

Cream -- Olive, canola, sunflower or safflower oil

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Health - The Great Fat Debate Continues