Dietary Carbohydrates

Question 1

How to calculate number of grams of carbohydrate consumed per day by an individual in energy balance

Answer 1

• [Weight (kg) * 30kcal/kg/day] * 50% carbs / 4kcal/gram.
• Ex. 70kg person * 30 kcal/kg/day
  
  • = 2100 kcal/day * 50% carbs
  • = 1050 kcal carbs / 4kcal/gram
  • = 262.5g carbs/day.
• With diabetes, adjust insulin accordingly (1 unit/15g carbs - varies by person)

Question 2

Carbohydrate classes in sugars

Answer 2

• (1-2 molecules)
• Monosaccharides, disaccharides, polyols (sugar alcohols)

Question 3

Components of monosaccharides

Answer 3

• Glucose
• Galactose
• Fructose

Question 4

Components of disaccharides

Answer 4

• Sucrose
• Lactose

Question 5

Components of polyols

Answer 5

• Sorbitol
• Mannitol
• Xylitol
• Hydrogenated starch hydrolysates

Question 6

Carbohydrate classes in oligosaccharides

Answer 6

• (3-9 molecules)
• Malto-oligosaccharides, other oligosaccharides

Question 7

Components of malto-oligosaccharides

Answer 7

Maltodextrins

Question 8

Components of other oligosaccharides

Answer 8

• Raffinose
• Stachyose

Question 9

Carbohydrate classes in polysaccharides

Answer 9

• (>9 molecules)
• Starch, fiber

Question 10

Components of starch

Answer 10

• Amylose
• Amylopectin

Question 11

Components of fiber

Answer 11

• Cellulose
• Hemicellulose
• Pectins

Question 12

Unique metabolic properties of fructose

Answer 12

• Enters cell via hexose transporter
• Skips PFK; enters glycolysis after pFK and speeds through to become pyruvate
• Rapidly cleared by liver –> increased TAG + insulin resistance
• If you eat too much, you may get fat
  
  • if EI > EE

Question 13

Properties of resistant starch

Answer 13

• Ex. corn starch.
• Used as thickening agent in many foods.
• Slowly absorbed due to crystal structure.
• Effects similar to those seen with high amylose carbohydrates.
• Used in children with inborn errors of metabolism that predispose them to hypoglycemia
  
  • (Problems with hepatic glucose production during fasting)

Question 14

Properties of fiber

Answer 14

• Complex carbohydrate not digestible by human intestinal enzymes –> pass through GI tract largely unaltered
• Increase stool volume, may lower cholesterol levels
• Higher levels of dietary fiber associated with lower risk of cancer
• Contained in husk of grains, source of some of the beneficial effects of whole grain products

Question 15

Glycemic index

Answer 15

• Looks at glucose (but not fructose, which is an issue with GI)
• Indicator of the ability of different types of foods that contain carbohydrate to raise blood glucose within 2 hours
• Foods containing carbohydrates that break down most quickly during digestion have highest glycemic index.
• Also called dietary index
• White bread has GI of 100 –> standard
• Higher glycemic index = larger glucose excursion (and vice versa)

Question 16

Glycemic load

Answer 16

• Glycemic index in consumed food
• Glycemic load = glycemic index of a given food * amount of food eaten

Question 17

Types of studies that can be used to inform nutritional recommendations

Answer 17

• Cellular/molecular studies
  
  • controlled and accurate
  • may lack applicability
• Animal studies
  
  • can control diet completely
  • but doesn’t necessarily translate to people
• Epidemiological studies
  
  • self-reported dietary intake correlated with disease
  • powerful due to large sample size
  • but not great because people lie
• Small RCTs with soft endpoints/surrogate markers
  
  • hard to get a lot of people to do things
  • may not be as powerful
• Large RCTs with hard endpoints
  
  • gold standard
  • but still not perfect because we don’t know that people are doing what they’re supposed to
  • Ex. Finnish Diabetes Study