2.2 Fats

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.

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.

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.