Dietary Fats Overview

Dietary Fats - Overview

• Dietary fats, also known as lipids, are essential for human health.
• Fats are insoluble in water but soluble in fat solvents.
• Fats, like carbohydrates, are primarily composed of carbon, hydrogen, and oxygen.
• Fats contain significantly more carbon and hydrogen than carbohydrates.
• Fats are a more concentrated energy source, providing 9 calories per gram, compared to 4 calories per gram for carbohydrates and proteins.

Dietary Fats - Objectives

• Identify essential fats and lipids.
• Describe the chemical nature and functions of these fats in the human body.
• List food sources of lipids and essential fatty acids.
• Determine appropriate fat intake for daily diets.
• Explain how the body digests, absorbs, and metabolizes fats.
• Understand the consequences of inadequate or excessive fat consumption.

Digestion of Fats

• Mouth: No chemical digestion; fat particles are broken down into smaller pieces mechanically, mixed with saliva.
• Stomach: Peristaltic movements mix food with gastric juice, and gastric lipase helps digest fats. The main fat digestion occurs in the small intestine.
• Small Intestine: Fats in the duodenum stimulate bile release from the gallbladder. Bile emulsifies fats; this increases the surface area for enzymes to work on. Pancreatic lipase digests fats further in the alkaline environment of the small intestine. Digested fat is broken into fatty acids, glycerol, and monoglycerides.

Absorption of Fats

• Via Hepatic Portal Vein: Medium chain fatty acids and monoglycerides are absorbed via the hepatic portal vein.
• Via Lymph System: Fatty acids and monoglycerides are taken up by the small intestine's mucosal cells. These are re-synthesized into triglycerides, forming spherical chylomicrons. Phospholipids, cholesterol, cholesterol esters, and apoproteins are added. Chylomicrons are lipoproteins. Water-insoluble triglycerides are now transported as lipoproteins.

Metabolism of Fats

• Absorbed fat can be oxidized to provide energy (CO₂ + H₂O + energy) or stored in fat deposits.
• Unlike carbohydrates with limited glycogen storage (0.5 kg), fats can be stored in much larger amounts.
• Carbohydrates can be converted to fat and stored.
• Fatty acids are not a primary glucose source but can produce ketone bodies that provide energy for cells, especially when glucose supplies are low.
• Most tissues, except the brain, can completely break down ketone bodies. This breakdown produces energy (CO₂ + H₂O + ATP).

Food Sources of Fats

• Many foods contain various amounts of fats.
• Visible fats are readily apparent (e.g., oils added to food, fried foods)
• Invisible fats are naturally present in foods (e.g., milk, egg yolks, oily fish, meat).

Plant Sources of Fats

• All oils (e.g., groundnut, sesame, soybean, rice bran, coconut, almond, cashew nut, corn, safflower, sunflower) and hydrogenated fats and margarine are sources of lipids.

Animal Sources of Fats

• Animal products like mutton, fish, poultry, milk, and milk products (butter, cream, yogurt, cheese), eggs, and organ meats.

Deficiency of Fats

• A deficiency of essential fatty acids leads to problems with cell membranes and their permeability.
• In infants, this results in dry, scaly skin lesions (eczema, skin lesions).
• A deficiency of fat-soluble vitamins and growth can be impacted in children

Excessive Fat Intake

• Fat consumption varies widely among regions and socioeconomic groups.
• Fats should comprise 20-25% of total daily calories.
• Excess fat intake causes obesity, increases blood cholesterol, and contributes to cardiovascular diseases.

Recommended Dietary Allowances

• Fat intake should be limited to no more than 30% of total daily calories.
• Saturated fat intake should be less than 10% of total calories.
• Polyunsaturated fatty acids (PUFAs) should contribute at least 10% of total calories.
• A correct ratio of omega-3 to omega-6 fatty acids is important to maintain good health
• Cholesterol intake should not exceed 180 mg/day.

Variety of Cooking Oils

• Using a variety of cooking oils ensures consumption of all essential fatty acids. -Non-vegetarians should use oils like groundnut, corn, soybean, and olive throughout the year. Fish eaters can use safflower and sunflower oil. -Vegetarians can use rice bran and corn oil.

Reducing Dietary Fat

• Use skim milk and milk products.
• Choose lean meats and trim visible fat.
• Use steaming, boiling, or poaching instead of frying.
• Replace high-fat dressings with low-fat or no-fat options.
• Choose fruit for dessert over baked items.
• Use herbs and spices for flavor instead of fat.
• Incorporate high-essential fatty acid options such as flaxseed and niger seeds.