Energy Value of Foods

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Energy Value of Foods
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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

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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
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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

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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)

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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
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Input and Output of EnergyEffects on Mass

• InputOutput ?mass maintained
• Inputltoutput ?loss of mass
• Inputgtoutput ?gain of mass
• The quality of what we eat is important as well

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Homework

1. 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 Lauries
   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

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Transformation of Food

• Mechanical and Chemical

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Mechanical transformation

• large pieces of food that are ingested have to be
  broken into smaller particles that can be acted
  upon by various enzymes

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Chemical Transformation

• uses water and digestive enzymes to break down
  molecules
• smaller molecules can be absorbed and utilized by
  the cells

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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 - - - -
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Absorption of Nutrients
Site of Absorption Nutrients Absorbed
Small intestine Glucose Amino acids Fatty acids Glycerol Water Vitamins minerals
Large intestine Water Vitamins minerals
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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 them
• B) nutrients from the chemical digestion of
  proteins
• C) contractions of the digestive tube allowing
  food to advance
• D) chemical secretion coming from the pancreas
• E) secretion allowing mechanical digestion of
  lipids
• F) contribute to chemical digestion of proteins
  in the stomach
• G) passage of nutrients from the digestive tube
  to the blood or lymph
• H) nutrients from the chemical digestion of
  carbohydrates

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• 3. Indicate in which digestive organ(s) each
  phenomenon takes place.
• A) peristalsis
• B) chewing
• C) action of gastric juices
• D) action of bile
• E) churning
• F) action of saliva
• 4. In which organ does chemical digestion of the
  following nutrients take place? In which organ
  does it finish?
• A) carbohydrates
• B) proteins
• C) lipids (fats)
• 5. What is the principal site of absorption of
  the following nutrients?
• A) water
• B) glucose
• C) minerals
• D) glycerol
• E) vitamins