Digestion, absorption and fate of macronutrients

Question 1

What is soluble fibre?

Answer 1

dissolves in water to form a gel-like material (helps lower cholesterol and blood glucose). Undergoes fermentation in colon to produce short chain fatty acids

Question 2

What is insoluble fibre?

Answer 2

promotes movement of material through digestive system

Question 3

What process are major macronutrients digested by?

Answer 3

hydrolysis (requires enzymes)

Question 4

What do disaccharides require for digestion?

Answer 4

brush border hydrolases

Question 5

Where are mono/di/polysaccharides digested?

Answer 5

in small intestine as monosaccharides

Question 6

Where are oligosaccharides digested?

Answer 6

large intestine, absorbed as SCFA

Question 7

Cause of primary lactose intolerance

Answer 7

loss of lactase at weaning (lactose not hydrolysed, metabolised in bowel into SCFA and gases

Question 8

How is lactose intolerance diagnosed?

Answer 8

H2 in breath (lactose malabsorption)

Question 9

Cause of secondary lactose intolerance

Answer 9

infection/illness causes reduced lactase expression

Question 10

Name sugar transporters

Answer 10

GLUT family - passive, SGLT family (sodium glucose transport) - active

Question 11

Describe the fate of dietary carbohydrate

Answer 11

glucose uptake by liver, muscle and other tissues, glycogen synthesis, oxidative disposal

Question 12

How are trans fats produced?

Answer 12

hydrogenation of unsaturated fatty acid

Question 13

How are triacylglycerols digested?

Answer 13

TAG emulsified by bile acids to form small micelles. Hydrolysed by pancreatic lipase which liberates fatty acids and forms 2-monoglycerol

Question 14

How is dietary fat absorbed in the small intestine?

Answer 14

fatty acids and monoglycerols enter enterocytes where they are re-esterified to form new triacylglycerols

Question 15

What happens to consumed cholesterol?

Answer 15

half enters absorptive cells where some is esterified into cholesteryl esters. Remainder lost in faeces

Question 16

How is dietary fat transported?

Answer 16

in the form of chylomicrons

Question 17

What are chylomicrons?

Answer 17

large lipoproteins produced in enterocytes used to transport dietary fats

Question 18

Composition of chylomicrons

Answer 18

mainly triacylglycerols and cholesterol esters in core. Surface composed of unesterified cholesterol, phospholipids and apoproteins

Question 19

Describe how energy from fatty acids is converted into ATP energy

Answer 19

oxidative disposal of dietary fatty acids by forming acyl coenzyme A

Question 20

How do dietary fatty acids accumulate in postprandial state?

Answer 20

in the form of triacylglycerol in adipocytes

Question 21

Functions of dietary fat

Answer 21

energy provision (oxidative disposal), energy storage (adipose and muscle triacylglycerol), structural role in cell membranes (phospholipids, cholesterol), provides EFAs, carry fat-soluble vitamins

Question 22

How are proteins digested in the stomach?

Answer 22

acid denatures proteins and unfolds them, zymogen (pepsinogen) activated to pepsin which hydrolyses 20% of proteins (including collagen) into di and tripeptides or amino acids

Question 23

How are proteins digested in small intestine?

Answer 23

by pancreatic proteases

Question 24

Examples of pancreatic proteases

Answer 24

trypsin, chymotrypsin, carboxypeptidase, elastase

Question 25

How are amino acids absorbed into the bloodstream from small intestine?

Answer 25

amino acids enter enterocytes via Na+ cotransporters and are then transported into the bloodstream by facilitated diffusion

Question 26

How are di- and tripeptides absorbed into the bloodstream from the small intestine?

Answer 26

di and tripeptides enter enterocytes by cotransport with H+ via PepT1. Digested by cytoplasmic peptidases into amino acids (or some remain intact)

Question 27

When does intact protein absorption occur?

Answer 27

in newborns for a few days to acquire passive immunity by absorption of immunoglobulins from colostral milk

Question 28

Role of insulin in the fate of dietary amino acids

Answer 28

insulin increases amino acid uptake in tissues, increases protein synthesis enzyme activity, reduces protein catabolic enzyme activity

Question 29

Which factors act to increase protein synthesis?

Answer 29

insulin, IGF (GH), testosterone, adrenergic influences, exercise

Question 30

Which hormones increase protein catabolism?

Answer 30

thyroid hormones, cortisol, (absence of insulin)

Question 31

Function of macronutrients

Answer 31

provide energy, building blocks, essential nutrients (cannot be made in body)

Question 32

Order the macronutrients from most to least energy dense

Answer 32

fats (9kcal/g), alcohol (7kcal/g) protein (4kcal/g), carbohydrates (4kcal/g)

Question 33

What percentage of the energy requirement does the British Nutrition Foundation recommend be obtained from carbohydrate, fat and protein?

Answer 33

48% from carbohydrate, 36% from fat, 16% from protein

Question 34

How does the CVD risk and mortality of obese unfit individuals compare to obese fit individuals (fat but fit)?

Answer 34

obese fit individuals have a lower risk of CVD and CVD mortality

Question 35

Causes of nutrient imbalance

Answer 35

inadequate intake, malabsorption, medical conditions, social factors

Question 36

Examples of medical conditions that can lead to nutrient imbalance / deficiencies

Answer 36

Crohn's disease, cystic fibrosis, bariatric surgery, parenteral or tube feeding, allergies, HIV infection, renal or hepatic disease (alter protein storage), psychiatric illnesses (e.g. EDs)

Question 37

What are essential nutrients?

Answer 37

nutrients needed in the body that cannot be synthesised in the body

Question 38

Examples of essential amino acids (EAAs)

Answer 38

isoleucine, phenylalanine, leucine, lysine, valine, methionine, threonine, tryptophan, histidine

Question 39

Examples of non-essential amino acids

Answer 39

alanine, asparagine, glutamine, serine, arginine, cysteine, glycine, aspartic acid, glutamic acid, proline, tyrosine

Question 40

Examples of essential fatty acids

Answer 40

n-6 PUFA: linoleic acid (LA), LC PUFA n-3 PUFA: alpha-linoleic acid (ALA), AA, EPA

Question 41

Function of essential fatty acids

Answer 41

cell membranes, biologically active compounds (e.g. eicosanoids), growth and development

Question 42

Where can omega 3 fatty acids be obtained from?

Answer 42

oily fish

Question 43

What is the recommended intake of carbohydrates for a non-physical active adult?

Answer 43

2.6-3.8 g/kg/BW

Question 44

What is the recommended intake of fat for a non-physical active adult?

Answer 44

0.8-1.2g/kg/BW

Question 45

What is the recommended intake of protein for a non-physical active adult?

Answer 45

0.8g/kg/BW