Energy Value of Foods

Main Sources of Energy for Cells Carbohydrates and lipids (fats) Proteins (in cases of illness or injury) Cellular respiration is the process which releases chemical energy from foods Glucose + Oxygen gas energy + carbon dioxide + water Carbohydrates: The most important source of energy. Makes up the largest part of our diets. a.   Source: Plants b.   Composition: Carbohydrates are made up of either a single sugar molecule or a chain of sugar molecules. Monosaccharide: One sugar Examples: Glucose (C6H12O6), Galactose, Fructose Disaccharide: Two sugars Example: Sucrose = Glucose + Fructose Polysaccharides: Many sugars Examples: Starch: stores energy in plants Cellulose –component of the cell wall in plants, cannot be digested by humans = fiber. Lipids Supply energy to the body. Difficult for the body to break down so you stay full longer. Storage compound: one gram of lipid contains about twice the amount of energy as one gram of carbohydrate or protein. Three groups: Fats, oils, waxes (waterproof coating of plant leaves) Phospholipids (cell membrane) Steroids (make hormones) Most common type of lipid = one glycerol and three fatty acids. Lipids are insoluble in water.   Proteins Proteins are used in cells to build cell structures and are used in chemical activities. Enzymes are proteins that aid in the reactions that occur during processes such as digestion and respiration. Proteins are composed of 20 amino acids arranged in different orders and of different lengths. There are 8 amino acids that are not made by the body. These essential amino acids must be obtained from the food we eat.

Energetic Value of Foods Energy Value The amount of energy a food can provide to an organism Expressed in kilojoules (kJ) The calorie (Cal) is often used on packaging 1 Cal= 4.184 kJ Energetic Value of Foods Vitamins, minerals, water do not give the cell any energy Carbohydrates Lipids (fats) Proteins 17kJ/g 37kJ/g

Energy Demands Basal metabolism Physical activities Digestion and absorption of what people eat (10% of daily energy or 1050 kJ) Teenagers 13-15 years old need on average 10 500 kJ of energy per day Basal metabolic rate- amount of energy required to perform vital functions such as heartbeat, respiration, basic cellular activities

Basal Metabolism Amount of energy required to maintain vital functions- heart beat, respiration, stable body temperature, cellular activities In general, more elevated in males than females (7000 kJ vs. 5500 kJ)

Nutritional Requirements To meet energy needs, a certain proportion of carbohydrates, lipids, and proteins is needed (vary with age, sex, size, physical activity) Energy values in … Carbohydrates Lipids Proteins % of Kilojoules (kJ) 55% of kJ ingested 30% of kJ ingested 15% of kJ ingested Grams (g) 340g 85 g 93 g Table of values represents requirements for adolescents

Input and Output of Energy Effects on Mass Input=Output mass maintained Input<output loss of mass Input>output gain of mass The quality of what we eat is important as well Changes due to… Change in amount of physical activity Change in amount of food consumed

Transformation of Food Mechanical and Chemical

Mechanical transformation large pieces of food that are ingested have to be broken into smaller particles that can be acted upon by various enzymes Mechanical Digestion - Food is crushed and liquefied by the teeth, tongue, and peristaltic contractions (waves of involuntary muscle contraction) of the stomach and small intestine. This creates a greater surface area for the digestive enzymes to work upon.

Chemical Transformation uses water and digestive enzymes to break down molecules smaller molecules can be absorbed and utilized by the cells The complex molecules of carbohydrates, proteins, and fats are transformed by chemical digestion into smaller molecules that can be absorbed and utilized by the cells. Does not completely break down all molecules Chemical Digestion - Many glandular structures, dispersed throughout the body, are involved in breaking food into simple molecules that can be absorbed. In the mouth, the salivary glands produce saliva, which both lubricates food and begins the process of starch digestion. Saliva contains salivary amylase (ptyalin), an enzyme that digests starch to maltose (a disaccharide). As food leaves the mouth, the esophagus conducts it to the stomach via the cardiac sphincter by means of peristaltic waves of smooth muscle contraction.

Organs of digestive system Mechanical transformation Glands Secretion from glands Foods transformed Results of transformation 1.Mouth Chewing Salivary Saliva carbohydrates Carbohydrates partially broken down 2.Pharynx Swallowing - 3.Esophagus peristalsis 4.Stomach Churning Peristalsis Gastric Gastric juices proteins Proteins partially digested 5.small intestine Emulsion of lipids by bile(secreted by the liver) churning pancreas Intestinal Pancreatic juices Intestinal juices Carbohydrates partially digested Lipids(fats) Glucose Amino acids Fatty acids Glycerol 6.large intestine During mastication, salivary glands secrete saliva to soften the food into a bolus (semi-solid lump) Once food gets partially broken down in the stomach, it becomes a thin watery liquid called chyme.

Absorption of Nutrients Site of Absorption Nutrients Absorbed Small intestine Glucose Amino acids Fatty acids Glycerol Water Vitamins minerals Large intestine Glucose; Amino acids; Fatty acids;Glycerol- biggest part of absorption Water;vitamins; minerals- start of absorption In large intestine- water; vitamins;minerals-biggest part of absorption