Carbohydrates

Question 1

What is the RDA for carbohydrates?

Answer 1

130 g/day, which is the glucose amount required by the brain, or about 50% intake

Question 2

Refined vs. unrefined carbohydrates

Answer 2

• Fruits, dairy, and whole grains, consist of carbs in their natural, unrefined state
• Refining carbs reduces their nutrient content and removes vitamins, minerals and fibre
• We need to be eating more unrefined carbs and reducing processed carbs
• similar in energy density, but nutrient density is much higher for the unrefined carbs

Question 3

Both sugar and artificially sweetened beverages are associated with…

Answer 3

Type 2 diabetes

Question 4

What is “whole grain”?

Answer 4

• All parts of the grain
• Bran: fibre and vitamins
• Germ: vegetable oils and vitamin E
• Endosperm: starch and some protein
• White flour only has the endosperm

Question 5

What are monosaccharides?

Answer 5

• Simplest building block of a carb
• Fruits, veg, and milk are natural sources
• All are 6-carbon sugars with the formula C6H12O6, but have different structures
• Glucose, galactose, and fructose
• fructose is found in fruits and is used widely as a sweetener as high fructose corn syrup

Question 6

What are complex carbohydrates?

Answer 6

• Polysaccharides
• Glycogen is the animal storage polysaccharide
• Starch is used for storage in plants
• Complex carbs like cellulose cannot be digested by human enzymes and thus is “fibre”

Question 7

Soluble vs. insoluble fibre

Answer 7

• Soluble fibres form gelatinous solutions with water, and can be partly digested in the large intestine by bacteria (oats, apples, beans)
• Insoluble fibre won’t dissolve in water (bran, fruit and veg peels)
• Both good but soluble extra beneficial because it promotes gut flora and lowers cholesterol

Question 8

How does fibre increase transit time?

Answer 8

By stimulating peristalsis

Question 9

What is the effect of fibre in the body?

Answer 9

• Speeds transit time but slows absorption
• Prevents huge release of insulin
• Stomach contents diluted with soluble fibre
• Prevents reabsorption of bile acids, thus lowering cholesterol because liver has to make more from body
• Higher stool weight
• Lowers cancer and CVD risk
• Important for healthy microbiota; provides food

Question 10

How much fibre do we need a day?

Answer 10

• At least 25 g

Question 11

How is glycolysis, the CAC, and ETC related?

Answer 11

• Pyruvate (3-carbon molecule) is converted to acetyl CoA (2 carbons) and CO2
• Acetyl CoA enters the citric acid cycle, produces more ATP, e-, and CO2
• Electron transport chain completes metabolism, using O2, yields ATP and H2O

Question 12

How does the availability of carbohydrates determine fatty acid metabolism?

Answer 12

• If carbohydrate is available, acetyl CoA from fatty acid oxidation has oxaloacetate to combine with in the CAC
• If no carbohydrate is available the liver can metabolize acetyl CoA to ketone bodies

Question 13

How does fibre affect the glycemic response?

Answer 13

• Slows sugar absorption
• Reduces spikes in blood sugar
• More curved response
• Also seen with fat and protein rich meals

Question 14

What is glycemic index (GI) and glycemic load (GL)?

Answer 14

• Glycemic index (GI) is a measure of blood glucose response to different carbohydrates compared with glucose
• Glycemic load (GL) is a calculation of available carbs in a food X GI
• GI calculated for 50g, portion sizes may differ, so GL can be used (low if < 11, high if > 20)
• A higher GI means a larger surge in blood sugar

Question 15

What foods have low GIs?

Answer 15

• High fibre, protein or fat foods

Question 16

What insulin-sensitive glucose transporter is present in muscle and adipose tissue?

Answer 16

GLUT4

Question 17

What are long-term complications of chronic hyperglycemia?

Answer 17

• Constant exposure to high levels of blood glucose causes glycation of proteins (covalent attachment of glucose such as occurs in HbA1c)), this is rationale for tight control of blood glucose
• These altered proteins are thought to link together, forming protein adducts called advanced glycation end-products or AGEs
• Cross-linking of vascular matrix proteins with plasma proteins may cause vessel narrowing increasing risk for retinopathy, nephropathy, stroke, MI, etc.

Question 18

What is diverticulitis?

Answer 18

• Excess pressure causes wall to bulge out in the colon, forms pouches called diverticula, leading to the condition called diverticulosis
• If fecal matter collects in the diverticula, it may cause pain, inflammation and infection - diverticulitis
• Fibre is thought to prevent this because it makes stool larger and softer, and thus more easy to pass

Question 19

How is diverticulitis treated?

Answer 19

• Lower fibre intake is recommended temporarily to reduce irritation, along with antibiotics to clear the infection
• Once the infection is resolved, increased fibre intake is recommended, along with increased fluid intake to keep stool soft

Question 20

How does fibre prevent colon cancer?

Answer 20

May be due to faster transit time allowing less contact of mucosal cells with toxins