Nutrition

Question 1

Nutrition

Answer 1

is the science that interprets the interaction of nutrients and other substances in
food (e.g. phytonutrients, anthocyanins, tannins, etc.) in relation to maintenance, growth,
reproduction, health and disease of an organism. It includes food intake, absorption,
assimilation, biosynthesis, catabolism and excretion.

Question 2

Energy intake is determined by the
‘macronutrient’ content of food.

Answer 2

Carbohydrates,
fat, protein and alcohol provide fuel for oxidation
in the mitochondria to generate energy (as
adenosine triphosphate (ATP)). The energy
provided by each of these elements differs:
• Carbohydrates (16 kJ/g)
• Fat (37 kJ/g)
• Protein (17 kJ/g)
• Alcohol (29 kJ/g).

Question 3

Factors that affect energy expenditure

Answer 3

❖ The basal metabolic rate (BMR) describes the
obligatory energy expenditure required to maintain
metabolic functions in tissues and hence sustain life. It is
most closely predicted by fat-free mass (i.e. total body
mass minus fat mass), which is lower in females and
older people.
❖ Extra metabolic energy is consumed during growth,
pregnancy and lactation, and when febrile. Metabolic
energy is also required for thermal regulation, and
expenditure is higher in cold or hot environments.
❖ The energy required for digestion of food (diet-induced
thermogenesis (DIT)) accounts for approximately 10%
of total energy expenditure, with protein requiring more
energy than other macronutrients.
❖ The level of muscular activity, which can vary
considerably with occupation and lifestyle.

Question 4

In response to starvation

Answer 4

❑ reproductive function is suppressed.
❑ BMR is reduced.
❑ profound psychological effects, including energy
conservation through lethargy.

Question 5

In the low-insulin state of starvation

Answer 5

fuels are
liberated from stores initially in glycogen (in liver and
muscle), then in triglyceride (lipolysis in adipose tissue,
with excess free fatty acid supply to the liver leading to
ketosis) and finally in protein (proteolysis in muscle).

Question 6

In response to over-nutrition

Answer 6

❑ BMR is increased.
❑ extra energy is consumed in the work of carrying
increased fat stores.

Question 7

In the high-insulin state of over-nutrition

Answer 7

excess
energy is invested in fatty acids and stored as
triglycerides; these are deposited principally in adipose
tissue but they may also accumulate in the liver (non-
alcoholic fatty liver disease) and skeletal muscle.

Question 8

In the absence of hypothalamic function

Answer 8

(e.g. in
those with craniopharyngioma) or in rare patients
with mutations in relevant genes (e.g. in leptin or
melanocortin-4 receptors), loss of response to
satiety signals, together with loss of adaptive
changes in energy expenditure, result in relentless
weight gain.