Human Nutrition: Topic D.1

Question 1

Distinguish essential and non-essential nutrients.

Answer 1

Essential nutrients

• cannot be synthesized by the body
• so they must be included in the diet

Non-essential nutrients

• can be synthesized by the body
• or have a replacement nutrient which serves the same dietary purpose
• so they are not necessary in the diet

Question 2

Discuss the causes and consequences of malnutrition, including protein deficiency malnutrition.

Answer 2

Causes:

• Caused by a deficiency, imbalance, or excess of nutrients in the diet
• Improper intake of nutrients (too much = overnutrition, too little = undernutrition) which can be caused by social/ socioeconomic factors, OR
• Improper utilization of nutrients by the body (illness/ disease/ malfunction in the hypothalamus)

Consequences:

• Starvation/ Wasting (too thin)/ Anorexia or Stunting (too short) are common in undernutrition (leading to the breakdown of body tissues/ organ failure)
• Obesity (overweight) is common in overnutrition (leading to CHD/ diabetes etc.)

Protein deficiency malnutrition:

• Caused by a lack of 1 or more essential amino acids, so that certain proteins cannot be synthesized
• Consequences include muscle loss, lack of blood plasma proteins, abdominal swelling, lethargy, physical and/or mental retardation, no menstruation

Question 3

Outline how leptin controls appetite and the consequences of leptin desensitization.

Answer 3

From a Markscheme: (Outline how leptin controls appetite)
a. leptin suppresses/inhibits appetite
b. is secreted by adipose tissue/fat «storage» tissue
c. level is controlled by amount of adipose tissue/«ongoing» food intake
d. leptin targets cells in hypothalamus/appetite control centre in brain
e. causes hypothalamus/control centre in brain to inhibit appetite
f. if amount of adipose tissue increases, blood leptin concentration rises

From a Quizlet and my memory because I literally could not find it anywhere in the notes:

• Increased leptin but a normal number of leptin receptors leads to a desensitization to leptin
• Leptin desensitization leads to a lack of satiety
• Leptin desensitization can lead to obesity

Question 4

Explain how to determine the energy content of food.

Answer 4

• By combusting (burning) a known mass of a food sample, the energy content of the food can be calculated by measuring the heat energy released from the burning food using a CALORIMETER (a vessel filled with a known quantity of water at a known temperature).
• Heat from the burning food is transferred to the water and the temperature increase of the water is used to calculate the energy content of the food sample (using the specific heat capacity of water: the amount of energy required to raise 1g of water 1℃ = 4.18 Joules)
• Energy Content of Food (Joules) = Mass of water (g) x 4.2 (J/g℃) x Temp increase (℃)
• What must be known/ kept constant in
  calorimetry:
• Mass of food sample
• Mass/ volume of water (1g = 1ml)
• Starting temperature of water
• Distance between calorimeter and burning food sample
• Note that error is often caused by heat loss to environment
  and/ or incomplete combustion of food sample

Question 5

Compare and contrast vitamins and dietary minerals.

Answer 5

• Both are needed in small quantities
• Minerals are inorganic / Vitamins are organic
• Minerals are ions / Vitamins are compounds

Question 6

Outline the causes and consequences of vitamin D deficiency and anorexia.

Answer 6

VITAMIN D DEFICIENCY
Causes:

• Not enough dietary sources (fish oils, egg yolk, enriched dairy products)
• Not enough exposure to UV light for body to synthesize

Consequences:

• Rickets:
• Develops in children when the bones near the growth plates do not mineralize properly
• Leads to irregular, thick & wide bone growth (decreased height/ bowed legs)
• Osteomalacia:
• Bone plates in adults are fully formed so you cannot develop rickets but you may develop a similar condition called osteomalacia = “soft bones” (painful/ weak bones, difficulty walking, increased fractures)

ANOREXIA
Causes:

• Caused by improper intake of nutrients (too little = undernutrition) which can be caused by social/ socioeconomic factors

Consequences:

• Body will begin to break down its OWN tissue as not receiving enough energy from diet (adipose (fat) tissue broken down first as fats contain more energy and their breakdown does not (usually) disrupt homeostasis/ metabolism - after adipose tissue broken down, muscle tissue broken down to provide proteins)
• IF enough bodily tissue is broken down, organs can become severely damaged and this can lead to death.
• In severe cases, body breaks down heart
  muscle (which can lead to death). As heart muscle atrophies and weakens, blood flow is reduced and blood pressure drops. Heart may also develop arrhythmias
  (irregular rhythms/ beats) due to electrolyte imbalances.

Question 7

Discuss the causes and treatment of PKU.

Answer 7

Causes:

• Phenylketonuria (PKU) = genetically inherited disease (autosomal recessive) caused by a person’s chemical inability to metabolize the aa phenylalanine (into tyrosine)
• (Phenylalanine builds up in tissues & bloodstream due to lack of enzyme (phenylalanine hydroxylase) that breaks phenylalanine down into tyrosine, from inheriting mutated form of gene
• Most common in European populations and less common in Asian, Latino, and African populations
• Excess phenylalanine may result in mental deficiency, behavioral problems, seizures & other developmental problems)

Treatment:

• Low-protein diet that limits intake of protein sources that contain phenylalanine
• Supplemented with a formula containing essential amino acids/ tyrosine