Dietary fat has critical roles in the body. Each gram of fat, whether it’s from a spoon of peanut butter or a stick of butter, provides 9 kcals. This caloric density is a lifesaver when food is scarce and is important for anyone unable to consume large amounts of food. The elderly, the sick and others with very poor appetites benefit from high-fat foods. Because their tiny tummies can’t hold big volumes, small children too need fat to provide enough calories for growth.
Fats are an energy reserve. Your body can store just small amounts of glucose as glycogen for energy, but you can put away unlimited amounts of energy as fat tissue. This is a problem in our world of excess calories, but was necessary in earlier times when food was scarce. You’ll use this stored energy while you’re sleeping, during periods of low energy intake and during physical activity.
Fats provide essential fatty acids (EFA). Our bodies are amazing machines capable of producing most of the needed fatty acids however there are two fatty acids that it cannot make at all, they are called LA (linoleic acid) and ALA (alpha linolenic acid). This makes LA and ALA “essential”, meaning they must be obtained through the diet. In the body, fatty acids are important constituents of cell membranes, and they are converted to chemical regulators that affect inflammation, blood clotting, blood vessel dilation and more.
Fats carry fat-soluble nutrients. Dietary fats dissolve and transport fat-soluble nutrients, such as some vitamins and also disease-fighting phytochemicals like the carotenoids alpha- and beta-carotene and lycopene. To illustrate, researchers were able to detect only negligible amounts of absorbed carotenoids in the blood of individuals who had eaten a tossed salad with fat-free salad dressing. With reduced-fat dressing, the study participants absorbed some carotenoids, but with full-fat dressing, they absorbed even more.11
Fats add to the texture and flavor of foods. You already know that fat makes food taste good. That’s partly because fats dissolve flavorful, volatile chemicals. They also add a rich, creamy texture, giving food a satisfying mouthfeel.
Fats in the Diet
The Acceptable Macronutrient Distribution Range (AMDR) is 20-35% for men and women age 19 years and older. For an adult consuming 1600 kcals then, the acceptable fat intake ranges from 35 to 62 grams daily. The AMDR for children is higher and varies by age, starting out at 30-40% for children ages 1 to 3 and gradually approaching the AMDR for adults. Experts discourage low-fat diets for infants, toddlers and young children because fat is energy-dense, making it appropriate for small, finicky appetites and to support growth and the developing central nervous system. The AIs for LA and ALA for adults range from 11-17 grams and 1.1 to 1.6 grams, respectively.
Because your body can make all the saturated fatty acids it needs, you do not need any in the diet. High intakes of most saturated fatty acids are linked to high levels of LDL (low-density lipoprotein), or bad, cholesterol and reduced insulin sensitivity.
We should limit our intake of saturated fatty acids to 10% of our total calorie intake (18 grams for someone eating 1600 kcals daily) to reduce LDL cholesterol and our risk for heart disease. The American Heart Association favors a greater restriction to just 7% of total calories (12 grams for a 1600 kcal diet).
What does bacon grease look like after the pan has cooled? Its firmness is a hint that bacon is high in saturated fat. Many saturated fats are solid at room temperature. Dairy fat and the tropical oils (coconut, palm and palm kernel) are also largely saturated.
The benefit you experience from reducing your intake of saturated fats depends on many factors, including what you replace them with. Loading up on fat-free pretzels and gummy candies may be tempting, but is a misguided strategy because diets high in heavily refined carbohydrates typically increase triglycerides and lower the beneficial HDL (high-density lipoprotein) cholesterol, both risk factors for heart disease.
A better strategy is to replace the foods rich in unhealthy fats with foods rich in healthy fats. Cooking with oils is better than cooking with butter or lard. A quick lunch of a peanut butter sandwich instead of a slice of pizza will do your heart some good. Trading out some of the cheese on your sandwich for a slice or two of avocado is another smart move. If your calories are in excess, switch from whole milk or 2% reduced-fat milk to 1% low-fat milk or nonfat milk to trim both calories and saturated fats.
Food manufacturers create both saturated and trans fats when they harden oil in a process called hydrogenation, usually to increase the shelf life of processed foods like crackers, chips and cookies. Partial hydrogenation converts some, but not all, unsaturated fatty acids to saturated ones. Others remain unsaturated but are changed in chemical structure. These are the health-damaging trans fats.
Many experts consider trans fats even worse than saturated fats because, like saturated fats, they contribute to insulin resistance14 and raise LDL cholesterol, but there’s more bad news. They also lower HDL cholesterol (the good cholesterol).
The American Heart Association recommends that we keep our trans fatty acid intake to less than 1% of total calories (less than 2 grams if consuming 1600 calories daily). Achieving this might be trickier than you realize because many foods touting No Trans Fats on their labels actually contain traces of these artery-scarring fats. That’s because the law allows manufacturers’ to claim zero trans fats as long as a single serving contains no more than 0.49 grams. If you eat a few servings of foods with smidgens of trans fat like margarine crackers and baked goods, you can easily exceed the recommended limit.
Identify traces of trans fats by reading the ingredients lists on food labels. Partially hydrogenated oil is code for trans fat. You know that there are at least traces of trans fat present. When oil is fully hydrogenated (the label will say hydrogenated or fully hydrogenated), it will not contain trans fats. Instead, the unsaturated fatty acids have been converted to saturated fatty acids.
As discussed, unsaturated fatty acids improve blood cholesterol levels and insulin sensitivity when they replace saturated and trans fats. There are two classes of unsaturated fatty acids: monounsaturated fats and polyunsaturated fats. Monounsaturated fat souces include avocados, nuts, seeds and olives. Peanut, canola and olive oils are additional sources.
There are several types of polyunsaturated fats, and they each have different roles in the body. • Omega-3 fatty acids have been in the spotlight recently because of their role in heart disease prevention. ALA is an omega-3 fatty acid, and you can find it in walnuts, ground flaxseed, tofu and soybeans, as well as common cooking oils like canola, soybean and walnut oils. Remember that your body is unable to create ALA, so it’s essential to get it in the diet. • Omega-6 fatty acids are a second type of polyunsaturated fats. LA is an omega-6 fatty acid and has to be acquired through the diet. Sources of omega-6 fatty acids are sunflower seeds, Brazil nuts, pecans and pine nuts. Some cooking oils are good sources too, such as corn, sunflower, safflower and sesame oils.16 • When you work on reducing whole-milk dairy, solid fats (like butter and bacon grease), and processed foods containing partially hydrogenated oils, be sure to replace them with unsaturated fats rather than simply adding extra calories to your usual diet. Otherwise you can expect to loosen your belt as you put on the pounds.
Don’t fear fats. Instead choose them wisely, making sure you do not exceed your calorie needs. Enjoy foods with monounsaturated and polyunsaturated fats while limiting the saturated and trans fats.