Good Fats versus Bad Fats -- Which are Which?
It seems the advice we get on dietary fats can change daily. "Eat less saturated fat -- intake more omega-3 fat." "Give up butter, use margarine. Wait, no margarine, use olive oil." As scientific understanding of dietary fats has grown, guidelines have become increasingly specific and meaningful.
We're going to take a look at fat intake guidelines from a scientific point of view, but don't worry we aren't going to nerd out here. We will also take a peak at the often cited Mediterranean diet which is a particular eating style known for supporting heart health despite high dietary fat intake. Finally we'll conclude with a strategic look at the right kinds and right amounts of lipid (fat) intake within the context of a healthy diet and lifestyle.
Introducing the Lipids
The lipids, or fats, in foods and the human body fall into three classes. About 95% are triglycerides. The other two are phospholipids (lecithin for example) and sterols (think cholesterol). When people speak of fats, they are usually talking about triglycerides. To keep this simple, we will be using the common term fat for this article. Fat is the bodies primary storage form for excess energy intake from food. Fat storage is a necessary evil, as it provided us the ability to survive times of famine or lowered energy intake.
Fat has many uses in the body. Fats are the body chief form of stored energy. As muscle fuel, fats provide most of the energy for muscular work (glycogen has a limit, fat storage is seemingly endless). Fats serve as an emergency reserve fuel supply during illness or diminished intake. Fats can be used as padding to help protect the internal organs, and can also provide insulation for us. Fats form the major material of cell membranes, a critical aspect of life. Fats also provide the raw material that is converted to other compounds, such as hormones, bile, vitamin D, etc.
Saturated versus Unsaturated Fatty Acids
Saturation simply refers to whether or not a fatty acid chain is holding all of the hydrogen atoms it can hold. If every available bond from the carbons is holding a hydrogen, the chain forms a saturated fatty acid. On the other hand, we have times where the chain has a place in which hydrogens are missing; an empty spot, or point of unsaturation. This is particularly common in the fatty acids of plants and fish. With one point of unsaturation, the fatty acid is called monounsaturated fatty acid. With two or more points of unsaturation, it is a polyunsaturated fatty acid. The degree of saturation of the fatty acids in a fat affects the temperature at which the fat melts. Generally, the more unsaturated the fatty acid, the more liquid the fat is at room temperature. Think olive oil (unsaturated) versus butter (saturated).
Two other types of fats, which are generally not good for you, are saturated fats and trans fats. Saturated fats are, as discussed, triglycerides in which most of the fatty acids are saturated, there are no "open spots" for hydrogen. Trans fats and what is formed during processing and contain any number of unusual fatty acids.
While most fats are a mixture of saturated, mono, and polyunsaturated fats, you should do your best to limit saturated and trans fat intakes. Some healthy fat choices that are rich in monounsaturated fats are olive, canola and peanut oils. Other vegetable oils such as safflower, sunflower, corn, walnut or soybean oil are rich in omega-6 polyunsaturated fats. Only a few oils provide significant omega-3 polyunsaturated fats, and those would be fish oils and flaxseed oils. Animal fats and the tropical oils of coconut and palm contain the most saturated fatty acids.
Beef tallow (beef fat), lard (pork fat), butter, etc are mostly saturated in nature and should be limited intake. Instead, focus on eating healthier fats such as avocados, healthy vegetable oils, fatty fish such as salmon, various nuts (almonds, cashews, peanuts, etc), flax and chia seeds, etc.
Healthy fats come in a variety of forms
Changing Lipid Guidelines
For a long time, the advice on lipid or dietary fat intake was simple. Cut out the fat for a healthy heart. Seems simple enough, no? Not so. While saturated fats have always been well established as "bad fats" leading to elevated cholesterol, dietary guidelines simply grouped all fats together and told us to eat "30% or less of our daily caloric intake in fat". While this was a good recommendation to cut down on saturated fat intake by reducing total fat intake, it also decreased the levels of our good fats.
Low fat diets are accompanied by several other challenges. For one, low fat isn't exactly equal to low calorie. Many of those with heart disease are overweight and need to reduce body fat to be more healthy. For another, low fat diets that are high in carbohydrates but low in fiber cause blood triglycerides to rise and HDL to fall with potentially negative effects on the heart.
Finally, low fat diets may cause people to cut out healthy nutritious foods. Fatty fish, seeds, vegetable oils, and nuts can all provide essential fatty acids, along with vitamins and minerals.
Low Fat Diets
That's not to say low fat diets do not have their place. A low fat diet remains and staple of the treatment plan for those with elevated blood lipids or heart disease (1). A low fat diet is therefore an important part of nutrition. However, this isn't an accurate representation of the majority. What about healthy people?
Research has given us evidence that has changed our recommendations for the healthy population. We no longer advise a "low fat" diet, but instead a "smart fat" diet. While fat intake was often linked to heart disease, this was strongly associated with high saturated fat intake, and weakly linked to total fat intake (2). These findings indicated that total fat intake was clearly not the cause of heart disease, rather something else was going on. When researchers examined high fat diets with a large amount of olive oil, but low saturated fat intake, they consistently saw low risk for heart disease. For those with diets of this type, the incidence of heart disease, certain cancers, and other chronic diseases is low and life expectancy is high (3).
Today's Lipid Guidelines
After reviewing the research and old guidelines, we now recommend a diet containing up to 35% of total calories coming from fat, but reduced saturated and trans fat intake. This is compatible with research showing low rates of heart disease, diabetes, obesity and cancer. The American Heart Association recommends replacing the "bad" saturated and trans fats with "good" unsaturated fats (4), within calorie limits of course. It has been made clear by the overseeing bodies of heart health and dietary intake that the human body has no need for trans or saturated fats, and the lower the intake the better (5).
Next time, we'll be checking in on more about the Mediterranean diet, and the different fat containing foods to learn more about making appropriate dietary selections.
(1) J. Putnam and S. Haley, Estimating consumption of caloric sweeteners, Economic Research Service, Farm Service Agency, and Foreign Agricultural Service, USDA, 2004.
(2) Economic Research Service, Estimated consumption of caloric sweeteners, Amber Waves, April 2003, available at www.ers.usda.gov/AmberWaves/April03/Indicators/behinddata.htm
(3) B.M. Popkin and S. J. Nielsen, The sweetening of the world's diet, Obesity Research 11 (2003): 1325-1332
(4) U.S. Department of Agriculture and U.S. Department of Health and Human Services, 2005 Dietary Guidelines Committee Report, 2005, available at www.health.gov/dietaryguidelines/dga2005report/
(5) U.S. Department of Agriculture and U.S. Department of Health and Human Services, Dietary Guidelines for Americans 2005, available online at healthierus.gov