Villain or Hero?: Understanding Dietary Fat
There are six nutrients that are needed by the human body for survival. Known as the essential nutrients, they include carbohydrate, protein, fat, vitamins, minerals, and water. Of these, dietary fat is perhaps the most misunderstood nutrient. Rather than being an evil villain, fat actually has many important functions within the body. For starters, fat is the most abundant fuel source available and can be a significant source of energy both at rest and during physical activity. In addition, fats are the major component of the outer covering of our cells, known as cell membranes. Fat insulates the body against loss of heat and cushions and protects vital internal organs such as the kidneys. Fats are also necessary for the absorption, transport, and storage of the fat-soluble vitamins (A, D, E, and K). While many fatty acids can be manufactured by the body, the essential fatty acids (linoleic and linolenic acid) must be obtained by dietary means. More on that a bit later.
What are the Different Types of Dietary Fat?
There are three major types of dietary fat; these include saturated, monounsaturated, and polyunsaturated. While all are relatively high in calories (9 calories per gram), they have differing effects on our health status. We will discuss each of these types of dietary fat below, and will also make some recommendations.
- Saturated Fats tend to be solid at room temperature and come mostly from animal sources such as fatty cuts of beef and pork, butter, and whole milk dairy products. Diets high in saturated fat tend to increase blood LDL cholesterol levels in most individuals, thus increasing the risk of cardiovascular disease. A high saturated fat diet is thought to be one cause of insulin resistance, a precursor to metabolic syndrome, prediabetes, and type 2 diabetes. As an aside, the word 'saturated' simply means that the chemical structure of these fatty acids is such that they cannot hold any additional hydrogen atoms.
Some saturated fats are liquid at room temperature and do not come from animal sources. The tropical oils are an example of liquid saturated fats. These include palm oil, coconut oil, and palm kernel oil. These also tend to increase blood LDL cholesterol levels.
It may interest you to know that there are different categories of saturated fatty acids; these include short chain, medium chain, and long chain. Some of the major saturated fatty acids in the American diet include palmitic, stearic, lauric, and myristic. While many of the saturated fatty acids such as palmitic, myristic, and lauric have the effect of raising blood LDL cholesterol levels, others such as stearic acid have little or no effect on LDL. Nevertheless, it is good public health policy to recommend an overall reduction in dietary saturated fat, which is a nonessential type of fat.
- Monounsaturated fats are “heart healthy” fats that are liquid at room temperature and come from vegetable sources. Oleic acid is an example of a monounsaturated fatty acid and is a major component of olive oil. Canola oil and avocados, as well as nuts and seeds also have a high monounsaturated fat content. Monounsaturated fats tend to decrease LDL cholesterol levels. Death rates from cardiovascular disease are relatively low in countries where diets are high in monounsaturated fat; these include many countries bordering the Mediterranean Sea. The word 'monounsaturated' means that two additional hydrogen atoms can potentially be absorbed by the fatty acid.
- Polyunsaturated fats are another type of heart healthy fat that is liquid at room temperature and come from vegetable sources. Linoleic acid, an essential omega-6 polyunsaturated fatty acid, is the most abundant fatty acid in the human diet. The other essential polyunsaturated fat is linolenic acid, an omega-3 polyunsaturated fatty acid. Examples of oils that are high in omega-6 polyunsaturated fat include corn oil, soybean oil, and safflower oil. Polyunsaturated fats tend to decrease LDL cholesterol levels. The word 'polyunsaturated' means that the fatty acid can potentially absorb at least four additional hydrogen atoms.
What Are Omega-3 Fats, And Why Do We Hear So Much About Them?
Omega-3 polyunsaturated fats are also known as fish oils. There is strong evidence That omega-3’s help to block blood clot formation and reduce resting blood pressure, inflammation, and blood triglyceride levels. They may also help to prevent fatal cardiac arrhythmias. Thus, the omega-3s are associated with a reduction in risk of heart attacks, strokes, and sudden cardiac death. Examples of long chain omega-3 polyunsaturated fatty acids include DHA and EPA; these are only found in fatty fish and fish oil supplements.
Many processed foods contain high levels omega-6 fatty acids such as the ones listed above. As a result, the American diet typically contains 20-25 times the amount of omega-6 as compared to omega-3 fat. Most health experts recommend increasing intake of DHA and EPA, while decreasing intake of omega-6 fatty acids, although the ideal ratio between the two has not yet been established. When using a fish oil supplement, be sure to check the label carefully. If your supplement is made mostly from ALA (an omega-3 found in walnuts and other plant-based foods), then use a brand such as Cooper Complete® that is made mostly from DHA and EPA. While walnuts are most certainly a heart-healthy food overall, ALA has not been shown to confer as much cardiovascular benefit as DHA and EPA. So to be clear, keep eating walnuts and other plant-based foods for good health. However, if your fish oil supplement is made mostly from ALA, then you should change brands.
Why Don’t I Hear Anything About Trans Fats Anymore?
Trans fats are formed through hydrogenation; a process by which hydrogen atoms are added to monounsaturated and polyunsaturated oils. In the past, manufacturers liked to use hydrogenated oils for two reasons. First, the shelf life of the product was increased by using these oils. Secondly, hydrogenation improved the texture of the product. Trans fat affects the body in much the same way as saturated fat. As an unwanted bonus, trans fat also decreases HDL cholesterol levels. In the past, fried fast foods, baked goods, and stick margarines typically contained a high amount of trans fat. Due to an FDA ruling, the use of trans fats by U.S. food manufacturers was banned in June of 2018. So, that’s why you haven’t heard much about trans fats lately!
So How Much Fat Should I Take In Each Day?
The current RDA states that fat should comprise 20-35% of total daily calories*. According to the most recent guidelines from the American Heart Association, only 5-6% of total daily calories should come from saturated fat.
Example: Matthew consumes 2500 total calories per day and wishes to obtain 25% of those calories from fat, with 5-6% of his total calories from saturated fat.
- 2500 calories per day x .25 = 625 calories from fat per day
- 625 calories divided by 9 calories per gram of fat = 69 grams of total fat per day
- 2500 calories x .05 = 125 calories = 14 grams of saturated fat per day.
- 2500 calories x .06 = 150 calories = 17 grams of saturated fat per day.
- Thus, Matthew should aim for only 14 to 17 grams of saturated fat per day; the remaining 52-55 fat grams per day should come from monounsaturated and polyunsaturated fat.
Practical Strategies for Reducing Dietary Saturated Fat Intake
- Select lean cuts of beef and pork, and limit portion sizes.
- Reduce consumption of butter and hard stick margarine. Soft tub margarines are a better choice. Use a vitamin D fortified low-fat spray margarine if you are watching calorie intake.
- Reduce consumption of fried fast food, lard, cream, and cream sauces
- Reduce consumption of pastry, cookies, doughnuts, cake, pie, and other baked goods.
- Reduce consumption of whole milk dairy products. Switch to reduced-fat dairy products or calcium and vitamin D-fortified soy products.
- Remove skin from chicken and turkey before cooking; select more white meat and less dark meat.
*The total number of calories per day required by an individual will vary according to age, sex, body weight, and level of physical activity, as well as goals. This link will provide an estimate.