fats & lipids
functions of fats
energy supply: fats provide energy for the body. each gram of fat yields 9 calories, which is significantly higher than carbohydrates and proteins (4 calories per gram).
structural component of body tissues:
- fats are essential for the structure of cell membranes (cell walls).
- they serve as protective padding for organs and bones, act as insulation from cold, and provide a feeling of satiety (satisfaction) after meals.
- adipose tissue protects organs and bones from injury.
nutrient transport:
- fats contain essential fatty acids required for various body functions.
- they act as carriers for fat-soluble vitamins: a, d, e, and k.
food sources of fats
animal sources
rich sources of fats include:
- red meats
- high-fat poultry cuts (thigh, wing)
- whole milk, cream, and butter
- cheeses made from cream
- egg yolks (the white contains primarily protein and water)
- fatty fish (tuna, salmon)
impact on cholesterol:
- saturated fats from animal foods can raise serum cholesterol, potentially leading to heart disease.
plant sources
rich sources of fats include:
- cooking oils (olive, sunflower, safflower, corn, canola, soybeans)
- nuts and seeds
- avocados
- coconut and cocoa butter
- margarine, salad dressing, and mayonnaise (often made from vegetable oils)
health benefits:
- plant fats do not raise cholesterol levels and are considered heart-healthy.
classification of fats
fats can be classified mainly into three categories: triglycerides, phospholipids, and sterols.
triglycerides:
- most prevalent type of fat, accounting for 95% of body lipids.
- composed of three fatty acids attached to a glycerol backbone.
- fatty acids can be classified as essential or nonessential:
- essential fatty acids (efas): cannot be synthesized by the body, must be obtained through diet, mainly long-chain polyunsaturated fatty acids derived from linoleic acid and linolenic acid.
- two families: omega-3 (beneficial for heart health) and omega-6 (linoleic acid which lowers cholesterol).
- omega-9 fatty acids are nonessential since the body can synthesize them if efas are present.
types of fatty acids based on hydrogen saturation
saturated fats:
- all carbon atoms in fatty acids contain the maximum number of hydrogen atoms, leading to a solid state at room temperature.
- high in animal foods such as meat, poultry, egg yolks, dairy products, and some plant foods like chocolate and coconut oil.
- recommendations: consume no more than 10% of total daily calories as saturated fats; the american heart association recommends 7% for those at risk of heart disease.
monounsaturated fats:
- contain one fewer hydrogen atom than saturated fatty acids at one position.
- primarily found in olive oil, peanut oil, avocados, etc.
- can lower ldl cholesterol when they replace saturated fats in the diet.
- recommended intake is about 20% of total daily calories.
polyunsaturated fats:
- contain two or more points of unsaturation (double bonds) in their structure.
- include omega-3 and omega-6 fatty acids, found in fish oils and some vegetable oils.
- natural food examples include soft margarines, oily fish, and various cooking oils.
- should not exceed 10% of total daily calories.
trans-fats and hydrogenated fats
trans-fatty acids (tfas):
- formed during hydrogenation (adding hydrogen to liquid oils to make them solid).
- found in baked goods and restaurant foods; they raise ldl and lower hdl cholesterol, increasing heart disease risks.
- required on food labels since 2006.
hydrogenated fats:
- made by adding hydrogen to polyunsaturated oils, converting them into saturated fats.
- present in margarine and serve as a common ingredient in processed foods.
cholesterol
cholesterol is a sterol found in animal foods and body tissues (not in plant foods).
production: the body synthesizes 800–1000 mg per day in the liver.
dietary sources: found in egg yolks, fatty meats, dairy (butter, cream), and organ meats.
cholesterol levels:
- normal levels should not exceed 200 mg/dl to prevent atherosclerosis.
- elevated levels contribute to plaque formation in arteries, which can lead to heart attacks and strokes.
effects on health
maintaining a balanced intake of fats is crucial to health:
- lowering serum cholesterol through dietary adjustments, increasing monounsaturated fats while reducing saturated and trans fats is recommended.
- soluble dietary fiber aids in lowering cholesterol by binding to it and preventing absorption.
digestion and absorption of fats
process overview:
- 95% of ingested fats are digested primarily in the small intestine.
- bile acids emulsify fats, while pancreatic lipase converts them to free fatty acids and glycerol for absorption through intestinal villi.
transportation of fats
fats, being insoluble in water, require lipoproteins for transport in the bloodstream.
types of lipoproteins:
- chylomicrons: largest lipoproteins, primarily composed of triglycerides (80-90%).
- very-low-density lipoproteins (vldls): made by the liver, carrying triglycerides mainly.
- low-density lipoproteins (ldls): carry cholesterol to cells and are linked to cardiovascular disease when elevated.
- high-density lipoproteins (hdls): transport cholesterol from cells back to the liver, often termed "good cholesterol".
- hdl levels below 40 mg/dl heighten heart disease risk, while levels above 60 mg/dl are protective.
metabolism of fats
largely controlled by the liver, which hydrolyzes triglycerides and synthesizes new ones as needed.
fat metabolism results in the production of carbon dioxide and water as by-products, which the body expels through various systems.
dietary requirements for fats
deficiency occurs when fat intake is less than 10% of total calories, leading to symptoms like eczema and retarded growth in infants.
excess dietary fat can lead to obesity and related diseases. recommendations vary:
- food and nutrition board suggests reducing fat intake to 30% of total calories.
- the american heart association's recommendations include limiting saturated fat to 7%, polyunsaturated fat to 10%, and monounsaturated fat to 20% of daily caloric intake.
health considerations
professionals should carefully evaluate dietary supplements claiming health benefits and educate clients on dietary changes for improved health.