2.3: Fats
By the end of this section, you should be able to:
- 2.2.1 Describe the nutritional function of fats.
- 2.2.2 Identify the impact of fats on wellness promotion and illness prevention.
- 2.2.3 Examine special considerations for individuals who face challenges securing adequate fat intake.
Fat Function and Metabolism
Fats are found primarily in animal foods such as meat, high-fat dairy products, and fried food, although plants are also sources of fat in the form of oils. Fat is a concentrated energy source, supplying more than double the caloric energy of carbohydrates or protein. See Table 2.4 for the comparison of energy in macronutrients . (Note that alcohol also provides calories, but unlike the macronutrients, it does not provide vitamins, minerals, or fiber. Its calories are commonly referred to as “empty” because they have no nutritional value.)
Fat helps maintain body temperature, is a critical part of fat-soluble vitamin transport, protects body organs by cushioning them, and is an essential component of cell membranes. Hormones secreted by accessory organs assist in fat metabolism . Although an enzyme, lingual lipase , exists in the mouth, the bulk of fat digestion occurs in the small intestine, where ingested triglycerides (fats composed of three fatty acids and one glycerol molecule) break down into monoglycerides and glycerol.
| Macronutrient | Calories (Energy) per Gram | Primary Food Source |
|---|---|---|
| Carbohydrate | 4 | Grains, fruits, vegetables |
| Fat | 9 | Meat and dairy products |
| Protein | 4 | Meats, nuts, legumes |
| Water | 0 | Municipal supply, well, bottled |
| Alcohol | 7 | Beer, wine, hard liquor |
Fat adds a smooth taste to foods and contributes to satiety . For instance, fat contributes to the flavor of a well-marbled steak, a loaded baked potato, chicken cooked with skin, cereal with whole milk, coffee with cream, and deep-fried fish with french fries. These foods are high in calories and saturated fats and may take twice as long to digest as carbohydrates, remaining in the stomach and intestine longer and staving off hunger pangs. During fat digestion, the intestinal cells secrete the hormone cholecystokinin , which slows pancreatic function and causes longer gastric emptying, making the person feel full (Borer, 2023).
The fat-soluble vitamins A, D, E, and K are found only in fat-containing foods. They travel through the blood with fat molecules from the small intestine and are stored in the liver until needed. Because the fat-soluble vitamins are stored in the body, there is no need for daily ingestion. The storage mechanism makes deficiencies rare in the United States except for vitamin D deficiency, which has seen a large uptick globally over the last decade. According to Guilbeau and Watson (2022), an estimated 18% of people in the United States have inadequate levels of vitamin D and 5% have vitamin D deficiency. Fat-soluble vitamin deficiencies may occur when fat is restricted or when a client receives total parental nutrition without lipids.
According to the U.S. Dietary Guidelines for Americans for 2020–2025 , no more than 20–35% of daily calories should come from fat; the exception is toddlers aged 2–3 years, for whom the goal is 30–40% (U.S. Department of Agriculture & U.S. Department of Health and Human Services, 2020). Fat is an essential nutrient critical for metabolic functions including vitamin synthesis, long-term energy storage, and the production of essential fatty acids. However, given its caloric density, too much fat, like too much carbohydrate or protein, can raise caloric intake above caloric output, causing weight gain .
Saturated Fat
A saturated fat is usually solid at room temperature and is found in animal-based foods and some plant oils. Saturated fat was first linked with heart disease in the 1950s by Ancel Keys, who proposed the diet–heart hypothesis (Teicholz, 2023). It has been widely accepted that a decrease in saturated fats is protective against the development of cardiovascular disease (MacDonald et al., 2022). The U.S. Dietary Guidelines for Americans 2020–2025 continue to include the recommendation to lower the intake of saturated fat. The American Heart Association recommends a dietary pattern that achieves 5–6% of calories from saturated fat. For example, if an individual needs about 2,000 calories a day, 120 calories at most should come from saturated fat, or approximately 13 g/day (American Heart Association, 2021). Table 2.5 lists amounts of saturated fat in some everyday foods.
| Food Item | Measure of Edible Portion | Saturated Fat Content (Grams) |
|---|---|---|
| Dried coconut, raw | 1 piece, about 2" x 2" | 13.4 |
| Trail mix, tropical | 1 cup | 11.9 |
| Chimichanga with beef | 1 chimichanga | 8.5 |
| Butter | 1 Tbsp | 7.2 |
| Cheddar cheese, cut pieces | 1 oz | 6.0 |
| Milk, whole (3.3% fat) | 1 cup | 5.1 |
| Pork salami, dry type | 2 3⅛" x ¹⁄₁₆" slices | 2.4 |
| Chicken thigh, roasted | 1 thigh | 1.6 |
Monounsaturated Fats
Monounsaturated fats (MUFAs) such as olive oil have become the “go-to” fat, replacing polyunsaturated fats, which received much of the attention in the 1980s. Table 2.6 lists some common oils and their monounsaturated fat content. All fats have the same number of calories per gram (9 g), whether saturated or not.
| Oil | Monounsaturated Fat Content (Grams per 1 Tbsp) |
|---|---|
| Safflower | 10.2 |
| Olive | 9.9 |
| Almond | 9.5 |
| Canola | 8.2 |
| Peanut | 6.2 |
| Soybean, hydrogenated | 5.8 |
| Sesame | 5.4 |
| Palm | 5.0 |
| Corn | 3.3 |
| Sunflower | 2.7 |
| Coconut | 0.9 |
There is a difference between animal monounsaturated and plant monounsaturated fats. Animal-based mono-unsaturated fats are present in eggs, poultry, red meat, fish, and full-fat dairy. Evidence demonstrates that research subjects who had “a higher intake of monounsaturated fatty acids from animals had a 21% higher risk of death from any cause” (American Heart Association, 2018). A decrease in mortality was observed when monounsaturated fats such as olive oil were substituted for saturated fats (Guasch-Ferre et al., 2019).
Polyunsaturated Fats
Two well-known polyunsaturated fats are omega-3 and omega-6 fatty acids. Omega-3 fats play a role in heart health and are found in eggs, soybeans, flaxseed, canola oil, and fatty fish such as salmon. The role of omega-6 fatty acid in heart health is more complex than that of omega-3. Its greatest effect appears to be strengthening of the immune system . Omega-6 fatty acids are found in sunflower, safflower, soy, sesame, and corn oils.
Polyunsaturated fatty acids are known for their health properties and anti-inflammatory action (Currenti et al., 2022). Polyunsaturated fats should make up no more than about 11% of the 20–35% of daily calories from fat (Liu et al., 2016). Table 2.7 presents a comparison of the polyunsaturated content of common cooking oils .
The majority of daily fat consumption should come from unsaturated sources, i.e., monounsaturated and polyunsaturated fats (Schweichler, 2022).
| Oil | Percentage of Polyunsaturated Fats |
|---|---|
| Flaxseed | 73 |
| Soybean | 55–58 |
| Corn | 59 |
| Cottonseed | 52 |
| Peanut | 32 |
| Sunflower | 29 |
| Canola | 32 |
| Safflower | 13 |
| Olive* | 11 |
| Butter** | 3 |
| Coconut** | 2 |
|
*High in monounsaturated fat (71%)
**High in saturated fat (butter: 63%, coconut: 87%) |
Trans Fats
Artificially produced trans fats have been used as food stabilizers in baked goods, snacks, and fried fast foods for more than 100 years (Amico et al, 2021). Trans fats make potato chips crisp and margarine spreadable, and they add texture to peanut butter. Trans fats also appear on food labels as partially hydrogenated oils , which are created when food manufacturers take unsaturated oils and mechanically add hydrogen ions, thereby making the liquid oil more saturated and partially firm.
Decades of research associating trans fats with elevated low-density lipoprotein (LDL), a significant cholesterol-carrying molecule in the blood, and lowered high-density lipoprotein (HDL), a protein/lipid molecule that removes cholesterol from the blood, coupled with much grassroots advocacy, resulted in mandated food labeling of trans fat in 2006. Yet, it took more than 25 years to enact a ban on artificial trans fats in food products from the time they were first noted to be harmful (Amico et al., 2021). Small amounts of naturally occurring trans fats are found in meat and dairy products. However, they do not appear to have the same negative impact as artificial trans fats and are not harmful if consumed in moderation (Bendsen et al., 2011).
Cooking and Food Preparation Techniques
Fat adds flavor to food, but most Americans consume more daily fat than recommended for heart health. Fat is an essential nutrient, and in a varied meal plan of whole grains, lean meats, and fresh fruits and vegetables, excessive dietary fat is not usually an issue. However, cooking techniques can take the healthiest of foods and add unneeded fat. A common example of a cooking technique that adds fat is deep frying, which can increase a food’s caloric content by 50% or more. Vegetables are low in fat, but when breaded and fried, the caloric and fat content climb, significantly reducing the health benefits. For example, battering and frying mushrooms, onion rings, and cauliflower change the nutrition profile by adding a significant amount of fat to a food group with negligible fat.
Alternatives to deep frying have emerged with the widespread marketing of countertop air fryers. This innovative cooking tool “fries” food with hot air and can save 70–80% of calories (Watson, 2021). Other more conventional ways to eliminate fat include grilling, baking, roasting, or boiling food items and adding flavor with seasonings or with low-fat rather than full-fat sauces. In baking, a 50% reduction of fat can be accomplished by substituting applesauce, canned pumpkin, pureed prunes, or mashed bananas for butter. (Using low-fat margarine in baking is not recommended because these products have added water and will affect the texture of the baked item.) Fat in the form of monounsaturated fatty acids can be added by sautéing vegetables in olive oil or by adding avocado or minimally processed peanut butter to toast.
Food preparation techniques, such as adding heavy dressing to a green salad, can also alter a food’s nutrition profile. Loading a baked potato with butter, sour cream, cheese, and bacon can increase its calories dramatically. Eating simple foods without high-fat enhancements is a real starting point for better health.
Special Considerations for Individuals Who Face Challenges Securing Adequate Fat Intake
Fat intake is a challenge for many people who consume a Western diet . However, the challenge is not securing adequate fat but controlling the overconsumption of fat. For more than 100 years, scientists and researchers have believed that fat plays a role in heart disease . Researchers are widely convinced that saturated fat increases LDL cholesterol and is a significant causal factor in the development of heart disease (Kris-Etherton & Krauss, 2020).
The lack of enzymes or emulsifying agents (i.e., bile) that help digest fat impacts dietary guidance on fat intake. Clients who have their gallbladder removed are encouraged to avoid high-fat, fried, and greasy foods, such as fatty sauces and gravies (Rajan, 2021), for at least a week after surgery.
Today, a “food replacement message” is this: Replacing saturated fat with polyunsaturated fat, or monounsaturated fat, and trading ultra-processed foods for a diet rich in whole, minimally processed foods may lower heart disease. This food replacement message resonates with the U.S. dietary guidelines and the U.S. Department of Agriculture’s MyPlate food guide and should be at the core of food literacy.