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

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

Carbohydrates Lipids (fats) Proteins

17kJ/g 37kJ/g 17kJ/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 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

Input and Output of EnergyEffects 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

Homework1. What is the average amount of energy (in kJ) that adolescents needs

for their daily activities? 2. a) What is the name of the energy required to maintain vital

functions? b) How much energy is required to maintain vital functions?

3. Laurie is a very active teenager. She trains several times per week with the swim team. The amount of energy she uses on a daily basis is 13200 kJ. State what would happen to Laurie’s mass in the long term if her food gave her the following amount of energy each day. i) 15 700 kJ ii) 10 300 kJ

iii) 13 200kJ

Transformation of FoodMechanical 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

Chemical Transformation

• uses water and digestive enzymes to break down molecules

• smaller molecules can be absorbed and utilized by the cells

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

•Peristalsis

pancreas

Intestinal

Pancreatic juices

Intestinal juices

Carbohydrates partially digested

Proteins partially digested

Lipids(fats)

Glucose

Amino acids

Fatty acids

Glycerol

6.large intestine

•churning

•Peristalsis

- - - -

Absorption of NutrientsSite of Absorption Nutrients Absorbed

Small intestine Glucose

Amino acids

Fatty acids

Glycerol

Water

Vitamins

minerals

Large intestine Water

Vitamins

minerals

Homework• 1. What are the two types of food transformation in digestion?Explain what

happens during each of these transformations

• 2. What are the names of the structures or processes described below?A) main facilitators of chemical digestion; digestive juices contain themB) nutrients from the chemical digestion of proteinsC) contractions of the digestive tube allowing food to advanceD) chemical secretion coming from the pancreasE) secretion allowing mechanical digestion of lipidsF) contribute to chemical digestion of proteins in the stomachG) passage of nutrients from the digestive tube to the blood or lymphH) nutrients from the chemical digestion of carbohydrates

• 3. Indicate in which digestive organ(s) each phenomenon takes place.A) peristalsisB) chewingC) action of gastric juicesD) action of bileE) churningF) action of saliva• 4. In which organ does chemical digestion of the following nutrients take place? In which organ does it finish?A) carbohydratesB) proteinsC) lipids (fats)• 5. What is the principal site of absorption of the following nutrients?A) waterB) glucoseC) mineralsD) glycerolE) vitamins